NOAA  Technical  Memorandum ERL  GLERL-15
WINTER CURRENTS IN LAKE  HURON
JamesH.  Saylor
Gerald S.  Miller
Environmental  Protection  Agency Report No,EPA-905/4-75-004
Great  Lakes  Environmental  Research  Laboratory
Ann  Arbor, Michigan
December 1976
UNITED STATES
DEPARTMENT OF COMMERCE
Juamta M. Kreps. Secretary
NATIONAL OCEANIC AND
ATMOSPHERIC ADMINISTRATION
Rchard A Frank Administrate!
Environmental Research
laboratories
VWmot N  Hess Oiteclor

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used or purchased because  of this NOAA Environmental Research
Laboratories  publication.
                                  11

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                                  FOREWORD

     This report presents  the  results of an investigation  of  water flow and
temperature structure  during winter  in Lake Huron.   Twenty-one current meter
moorings were deployed in  the  lake in November  1974  and retrieved approximately
6 months later.   Collected data were analyzed to  determine the character of
current flow during  conditions  of an almost isothermal  lake water  mass.   This
study was a  cooperative effort of the National  Oceanic  and Atmospheric Admin-
istration's Great  Lakes Environmental Research  Laboratory,  the Canada Centre
for Inland Waters,   and Region V of the  Environmental Protection Agency. It
was partially supported by the Environmental Protection Agency through an Inter-
agency Agreement and is a contribution  to  the  International Joint Commission
Upper Lakes Reference  Study.   The authors  are particularly grateful  to Dr.  E.
B. Bennett of the  Canada Centre for  Inland Waters  for his  arrangement for and
coordination of Canadian participation  in the study and to Mr. R. J. Bowden of
the Environmental  Protection  Agency,  Region V,  for his  generous support of
field operations from  the  .Research  Vessel  Roger R. Simons,
                                       111

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                                  CONTENTS
Abstract
1.
4.
INTRODUCTION

METHOD

RESULTS

3.1 The  Character of the Wind  Field

3.2 Water Temperature Structure

3.3 Seasonal  and Monthly Current  Patterns

3.4 Episode Analysis

3.5 Effects of Ice Cover
Page

  1

  1

  4
                                                                             8

                                                                            11

                                                                            16

                                                                            20
3.6 The  Annual Cycle of the  Variation of Current  Speeds  with Depth 23

3.7 Comparison of Summer Current  Patterns                            26

CONCLUSIONS                                                           28

REFERENCES                                                            31
Appendix A.     MONTHLY AND  SEASONAL  WATER CURRENT TRANSPORT AND WIND RUN
               ROSES  FOR CONDITIONS OBSERVED IN LAKE HURON DURING WINTER
               1974-75                                                      34

Appendix B.     WATER  CURRENT  TRANSPORT  AND WIND RUN ROSES  FOR  SELECTED
               EPISODES  OF  DIRECTIONALLY  STEADY WIND STRESS IN LAKE  HURON
               DURING WINTER  1974-75                                       67

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                                    FIGURES

                                                                           Page

 1.   Location map showing  current  meter  mooring sites and  Lake  Huron
     bathymetry.                                                             3

 2.   Summary of data  returned  from each current meter deployed  in Lake
     Huron during winter 1974-75.                                            5

 3.   Comparison of  air  temperature measurements at  meteorological
     stations near the west  coast  of Lake Huron and  water  temperatures
     at 15 m depth  at nearby current meter moorings  during  winter
     1974-75.                                                                 1

 4.   Monthly wind speeds  measured  at five meteorological  stations
     about the perimeter  of  Lake Huron.                                      8

 5.   Monthly mean water  temperatures  from Lake Huron's  deep northeastern
     basin  (mooring 113).  the  northern part of the  lake off Alpena, Mich.
     (mooring 109) .  and  the  southern end (mooring 101) .                      9

 6.   Monthly mean water  temperatures (C)  at  15 m depth during  February
     1975 in Lake Huron.   Distributions  in the eastern  parts  of the
     lake are assumed,  but tee was present along  the east coast,  indicat-
     ing the presence of  near  0C  water.                                     10

 7.   Water temperature distribution  across  the mid-lake ridge.              11

 8.   Vector  resultant current  flows  in  Lake  Huron during winter 1974-75.    16

 9.   Side-Looking Airborne Radar Image  showing the ice  cover  on western
     Lake Huron on  12 February 1975.                                         21

10.   Vector  resultant current  flows  in  Lake Huron during  9-15 February
     1975.                                                                    22

11.   Vector  resultant current  flows  in  Lake Huron during  26 February-6
     March 1975.                                                              22

12.   Monthly mean current  speeds at  the  four  levels  of  measurement in
     Lake Huron during winter  1974-75.                                       24

13.   Lake-wide average of  the  RMS  current speed at  four depths  observed
     in Lake Ontario  during  1972.                                            25

14.   Surface water  flow  patterns in  Lake Huron during the  open  water
     navigation season.                                                       27

15.   Flow patterns  of epilimnion water in  Lake Huron during summer.         27
                                       VI

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16.   Surface water  temperatures (C) of Lake  Huron as observed in 1971
     on three CCIW  monitor  cruises.                                         29

17.   Temperature  isopleths  (C) of the Lake Huron water mass on a cross
     section of  the lake from  Black  River, Mich., to Tobertnory, Ont,,
     for the cruise intervals of Figure 16.                                 30
                                      VII

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                               APPENDIX FIGURES

                                                                            Page

A. la.     Water  current transport roses at 15 m depth in  Lake Huron
          and  wind run roses  at  five  perimeter meteorological stations
          for  November  1974.                                                 35

A. Ib.     Current  roses at 25  m  depth  for November 1974.                    36

A.lc,     Current  roses at 50  m  depth  for November 1974.                    37

A. Id.     Current  roses at 2 m above  the  bottom for November  1974.          38

A.2a.     Current  roses at  15  m depth and wind roses for  December
          1974.                                                              39

A.2b.     Current  roses at 25  m  depth  for December 1974.                    40

A.2c.     Current  roses at 50  m  depth  for December 1974.                    41

A.2d.     Current  roses at  2  m above the bottom for December  1974.          42

A.3a.     Current  roses at  15  m depth and wind roses for  January
          1975.                                                              43

A.3b.     Current  roses at 25  m  depth  for January 1975.                     44

A.3c,     Current  roses at  50  m depth for January 1975.                     45

A. 3d.     Current  roses at  2  m above the bottom for January  1975.           46

A.4a.     Current  roses at 15 m  depth and wind roses  for February  1975.    47

A.4b.     Current  roses at  25  m depth for February 1975.                    48

A.4c.     Current  roses at  15  m depth for February 1975.                    49

A.Ad.     Current  roses at 2  m above the bottom for February  1975.          50

A.Sa.     Current  roses at  15  m depth and wind roses for  March 1975.        51

A.Sb.     Current  roses at  25  m depth for March 1975.                        52

A.5c.     Current  roses at 50  m depth  for March 1975.                        53

A. 5d.     Current  roses at 2 m above  the  bottom for March 1975.             54

A.6a.     Current  roses at  15 m depth  and  wind roses  for April 1975.       55

A.6b.     Current roses at  25  in depth for April 1975.                       56


                                      viii

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A, 6e,      Current roses at  50  m depth for April 1975.

A,6d.      Current roses at 2  m above the bottom for April  1975.

A. 7a,      Current roses at 15 m depth and wind  roses  for  May 1975.

A.7b,      Current roses at 25 m depth for May 1975.

A,7c.      Current roses at 50 m depth for May 1975.

A,8a.      Current roses at 15 m depth and wind roses  for winter 1974-75.

A.8b.      Current roses at 25 m depth for winter  1974-75.

A.8c.      Current roses at 50 m depth for winter  1974-75.

A.8d.      Current roses at 2  m above  the bottom for  winter  1974-75.

B.la.      Current roses at 15 m depth and wind  roses  for 20-22  November
           1974.

B.lb.      Current  roses at 25 m depth for 20-22  November  1974.

B.lc.      Current roses at 50 m depth for 20-22  November  1974.

B.ld.      Current roses at 2   m  above  the  bottom for  20-22 November 1974.

B.2a.      Current  roses at 25 m depth for 30  November-2  December  1974.     72

B.2b.      Current  roses at 25 m depth for 30  November-2  December  1974.     73

B.2c.      Current roses at 50 m depth for 30  November-2  December  1974.     74

B,2d.      Current roses at 2  m above  the  bottom for  30 November-2
           December 1974.                                                     75

B,3a.      Current roses at 15 m depth and wind  roses  for 26-29  December
           1974.                                                              76

B.3b.      Current roses at 25 m depth for 26-29 December  1974.             77

B.3c.      Current roses at 50 m depth for 26-29 December  1974.      ,       78'

B.3d.      Current roses at 2   m  above  the  bottom for  26-29 December 1974.   79'

B.4a.      Current roses at 15 m depth and wind  roses  for Y-ll  January
           1975.                                                              80'

B.4b.      Current roses at 25 m depth for Y-ll  January 1975.               81"
                                                                               !
B.Ac.      Current roses at 50 m depth for Y-ll January 1975.               82'
                                        IX

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B.4d.      Current roses at 2 m above the bottom for Y-ll  January 1975.     83

B.5a.      Current roses at 25 m depth and wind roses for  11-14 January
           1975.                                                            84

B.5b.      Current roses at 25 m depth for 11-14 January 1975.              85

B,5c.      Current roses at  50 m depth for 11-14 Janyary  1975.             86

B.5d.      Current roses at 2  m above the  bottom for 11-14 January 1975.   87

B,6a.      Current roses at 15 m depth and wind roses for Y-15 February
           1975.                                                            88

B.6b.      Current roses at 25 m depth for 9-15 February 1975.              83

B.6c.      Current roses at 50 m depth for Y-15 February 1975.              90

B.6d.      Current roses at 2 m above the  bottom for  Y-15  February 1974.    91

B. 7a.      Current roses at 15 m depth and wind roses for  26 February-6
           March  1975.                                                      92

B.7b,      Current roses at 25 m depth for  26  February-6  March 1975.       93

B.7c.      Current roses at 50 m depth for  26  February-6  March 1975.       94

B.7d.      Current roses at 2 m above the bottom for 26 February-6 March
           1975.                                                            95

B.8a.      Current roses at 15 m depth and wind roses for 1-8  April  1974,  96

B.8b.      Current roses at  25 m depth for  1-8 April 1975.                 97

B.8c.      Current roses at 50 m depth for  1-8 April 1975.                 98

B.8d.      Current roses at 2 m above the bottom for  1-8  April 1975.       99

B.9a.      Current roses at 15 m depth and wind roses for 3-13 April
           1974.                                                            100

B.9b.      Current roses at 25 m depth for  3-13 April 1975.                101

B.9c.      Current roses at 50 m depth for  3-13 April 1975.                102

B.9d.      Current roses at 2 m above the bottom for  3-13 April 1975.      103

B.lOa.     Current roses at 15 m depth and wind roses for 3-J May 1974.    104

B.lOb.     Current roses at 25 m depth for  3-7 May  1975.                   105

B.lOc.     Current roses at 50 m depth for  3-7 May  1975.                   106


                                       x

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                         WINTER CURRENTS  IN  LAKE HURON*

                     James H. Say lor and Gerald  S.  Miller

           Twenty-one  current meter moorings were  deployed in Lake  Huron
     during  winter  1974-75.   The moorings were  set in November 1974  and
     retrieved  approximately 6  months later.   The stations were  configured
     on  a  coarse  grid to measure the  lake-scale circulation during winter.
     Water temperature  was  also recorded in nearly all of the 65  current
     meters  deployed.   Results reveal a  strong  cyclonic  flow pattern in
     the  Lake  Huron Basin persisting  throughout the winter.  The  observed
     winter  circulation  was  in essence very similar  to what is now
     believed  to  be the summer circulation  of epilimnion water,  although
     the  winter currents penetrated to deeper levels  in the water  column
     and  were  more  intense.   Winter cyclonic  flow persisted in a  nearly
     homogeneous  water  mass, while  summer currents exhibited an  almost
     geostrophic  balance with observed water  density distributions.
     This  suggests  that the current  field driven by prevailing wind
     stresses  across  the lake's water surface may be  largely responsible
     for  establishing  the horizontal  gradients  of water density ob-
     served  in  the  lake during summer.  Analyses  of energetic wind
     stress  impulses  reveal the prevailing  wind directions that drive
     the  dominant circulations.   The  winter  studies permit a descrip-
     tion  of the  annual cycle  of  horizontal current speed  variation
     with  depth in  Lake Huron,  and  in the other Great  Lakes as well.
     The  effects  of ice cover are  examined  and  the distribution and
     movement of  the  ice cover with respect to  lake current and
     temperature  fields  are discussed.
                              1.   INTRODUCTION

     This  report  presents  the results of  an  investigation of the  character  of
winter current  flow  in Lake Huron.   The  investigative effort was  undertaken
during winter  1974-75  as a part  of  the  International Joint  Commission  Upper
Lakes Reference  Study.   The current  surveys  were accomplished through  a  coopera-
tive effort  of the Great Lakes  Environmental Research Laboratory  (GLERL)  of the
National Oceanic  and Atmospheric Administration,  The  Canada Centre  for  Inland
Waters  (CCIW),  and the United  States  Environmental  Protection Agency  (EPA),
Region V.  The  study reported here represents  the first serious attempt  to
describe the winter  circulation of Lake Huron.

     The earliest study of Lake  Huron currents was reported by Harrington.  (1895)
Drift bottles  were released from  cargo  ships traversing Lake Huron  during  the
summers  of 1892  and  1893.   By  correlating  release and recovery points  of the
drift bottles,  he deduced  a prevailing  cyclonic  flow pattern of Lake  Huron
surface  water,  noting  especially a persistent  southward flow along  the  entire
length of  the  lake's west  coast.  Water moving southward along this  shore  was
observed to  return northward along the  lake's  east  coast,  closing the  circula-
tion pattern  to form essentially a single  cyclonic  cell.  We shall  return to
*GLERL Contribution No.  111.

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Harrington's observations  later  in this report as  the  winter observations
reported here  reveal  some  remarkable comparisons with  this  early effort to
describe currents.

     Ayers et  al.  (1956)  performed three multiship  synoptic  surveys of Lake
Huron during the  summer of 1954,  observing on  several  Lake  Huron cross sections
distributions  of  physical,  chemical,  and biological  properties  of the water
mass.   Using the  observed  water temperature distributions and  a dynamic height
method developed  for  fresh water to compute geostrophic  currents,  they deter-
mined current  flows from the  water density field for each survey.   The current
patterns determined were in general more complex than  Harrington's  results,
although there  were  certain similarities in the  reported cyclonic character
of the gross circulation.

     In  the  summer of 1966, the Federal  Water  Pollution Control Administration
 (FWPCA)  performed extensive measurements of currents in  Lake Huron  by mooring
a large  number  of current  meters at numerous open lake locations.   Subsequent
to this  data collection effort,  reorganization within  the  Federal government
placed this activity  within the  EPA.   Changing program priorities prevented
timely analyses  and  reporting of these surveys.  As part of the International
Joint Commission  Upper  Lakes Reference  Study,  GLERL  undertook  analyses of these
current  data  and  the results were reported by Sloss and Saylor (1975) .  This
effort was  subject to many shortcomings because  of  inherent instrument limita-
tions in the generation  of current meters used in the  surveys  and the loss of
documentation in  the  interval  between data collection  and analysis.    In spite
of these shortcomings,  evidence  of a general cyclonic  lake  circulation was
revealed to support the  nature of the  gross summer  current  patterns  reported
previously.

     All of these previous investigative programs were performed during summer
and fall, when  the Lake  Huron water mass is typically  density  stratified.
Several  current meter moorings  were set along the west coast of the lake dur-
ing winter  1965-66 by FWPCA,  but  the  effort was  unsatisfactory  for determining
large-scale characteristics of  winter  circulation  (FWPCA,  1967).  With the
near absence of  any  knowledge of winter currents in Lake Huron, the  program
described in this  report was  initiated.   The winter season  is  characterized by
an almost isothermal  water mass  in Lake Huron,  as is  true of the other Great
Lakes as well.    Circulation during this long season of nearly  homogeneous
water in the lake basins  has received very  little  attention, primarily because
of the difficulties  and  rigors of working during  the severe weather  associated
with winter on the Great Lakes.

     The bathymetry of Lake Huron  is  shown in Figure 1.   Also   shown in the fig-
ure are  locations  of  the  21 current meter moorings  placed in the lake during
the winter  of  1974-75.   Comparison of the bottom  topography with station  config-
uration  gives  some idea of the  plan of study,   which we will discuss in more de-
tail later in  this report.   The geology of the  region played an important role
in shaping the  Lake Huron  Basin.   The north shore  of the lake,   along  the  North
Channel  and northeastern shore  of  Georgian Bay,  is  on the edge  of the Precam-
brian Canadian Shield.   The lake basin  otherwise was  carved out of the Paleozoic

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 Figure 1.   Location nap  showing current
   meter  mooring sites and Lake Huron
   bathymetry.   Only  the  SO and 100 m
   contours  are  shown as  the  bottom in
    the deep northeastern basin is  very
   irregular, ezeeedirig depths  of  150
   m  in over  30 percent of its area .
                                                ^Sault Ste. Mane
                                                             LAKE HURON
                                                      'Bay City

                                                   MICHIGAN
                                                 SCALE IN KILOMETERS
                                                       ~80SOTOO
                                                                HurornFSarnia
 rock province of  the  region (Hough, 1958).   Resistant formations within  the
 Paleozoic province may be  correlated  with the major bathymetric features of
 the lake bottom.   Niagara  Dolomite is the hard,  erosion-resistant formation
 that forms the Lake Huron  shoreline  for  a distance of nearly 60 km east  of  the
 Straits of Mackinac.   It continues  southeastward  to form the southern and  south-
 western shores  of the chain  of  islands  separating Lake Huron from Georgian  Bay
 and the Bruce Peninsula.   Along the  Michigan  shore,  resistant  formation^ of the
 Rogers  City and Traverse Group  formed lake shores and headlands from Thunder
 Bay at  Alpena, Mich.,  northward to Presque Isle, Mich.  From Thunder Bay south-
 eastward,  the underwater extensions  of  these  resistant formations formed  the
 most important  bathymetric  feature of the  lake  basin,  a ridge  that extends
,  across the lake  to Clark Point on the Canadian shoreline nearly 15 km southwest
 of Kincardine,  Ont.   This ridge is a very  prominent feature of basin topography
 and it  rises to within 11  m  of  the lake  surface near the middle of the lake at
 Six Fathom Bank.   The northeastern face  of the  ridge is very steep as the  lake
 bottom descends to depths  exceeding 200 m, while  the ridge  itself is  generally
 30 to 60 m deep.   Southwest  of  the  ridge the  lake bottom descends more gradu-
 ally to depths  of 70  to 100 m.  Thus,  the southeastward trending ridge sepa-
 rates the lake  into two distinct basins.

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     I"  this  report  we  will  present evidence that there is in  fact  a  prevailing
and dominant  patter"  of water  current  flow in Lake Huron during winter.   season-
al and monthly current roses of water transport  will  be presented,  and  the  re-
sponse of  the lake  to episodes of strong and steady  wind  stress will  be  examined.
The winter Studies make  possible  a description of the  annual  kinetic  energy cycle
of the Lake Huron water mass.
                                  2.   METHOD

     Twenty-one current meter  moorings  were Set in Lake Huron  during  the latter
half of November 1974.  Each mooring consisted of a  string  of  current meters
suspended on  a  taut  line  beneath a subsurface float.    Current  meters  were  planned
for placement at  uniform  depths  of 15,  25, and SO m  below the  water  surface and
at 2 m above  the  bottom;  actual  depths  of the current  meters deployed varied
only slightly from the planned depths.   Most  of the moorings were  Set in water
about 50 m deep and  included three current meters.    Three moorings were Set in
much deeper water  and included the full complement of  four  current meters.   Cur-
rent meter depths  on each mooring and the length of  record  obtained  from each
meter are summarized  in Figure 2.   Moorings numbered 114 and 117  were not re-
covered in the  spring of  1975, having been lost in regions  of  large  surface wave
stress  during winter  storms.

     Twelve  moorings were  deployed by CCIW  from  the  Canada Survey Ship Limnos.
Current meters on these moorings were a mix of Plessey model M021's and Geodyne
model 850's. All of the current  meters  had a" integral temperature recorder.
The remaining nine moorings  were deployed  from the EPA Research Vessel  Roger
/?. Simons and  included a  mix of AMF vector averaging current meters  and Geodyne
model A-100's.  Only the  AMF meters had a"  integral temperature recorder on
these moorings.   All  of the winter moorings included an acoustic  release just
above each mooring's  sinker  for  recovery  in the spring  of 1975  and a  ground
line of several hundred meters  of polypropelene for recovery with  a grapnel in
the event of  release  failure.

     No other measurements  were  attempted during the course of the winter  cur-
rent meter deployments.   It was felt that  existing meteorological stations
around the perimeter  of the lake were sufficient for adequate  description  of
wind and air  temperature  fields  influencing Lake Huron.  Many  of  the  current
meter stations  were  placed  fairly  close  to shore (10  to 20  km)   St  a water  depth
of about 50 m.  The  placement of current meters "ear the lake  boundaries was
based on considerations of  the present knowledge of  lake  circulations during
the density  stratified season as all of the lakes have revealed that  the strong-
est and most  persistent currents are observed within the first  20  km  or there-
abouts  lakeward of  the coasts.  Flow in the  coastal  strips in long-term averages
is essentially  parallel with the bathymetric  contours  and during  summer these
regions are  characterized by strong, though variable,  horizontal  density grad-
ients.   I"  retrospect,  the  placement of current meters "ear  the lake  boundaries
was a good choice as the  results presented herein will illustrate.   Other  areas
of current meter  concentrations  included  the  mouth of  Saginaw  Bay  and the south-
eastern section of  the ridge sepaiating the  lake into  two distinct basins.

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111
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114 mooring not recovered
117 mooring not recovered
Figure 2. Summary  Of  data returned from  each current meter deployed in
                   Lake Huron during winter 1974-75.

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                                  3.  RESULTS

                     3.1 The Character  of the Wind  Field

     Great  Lakes  weather is characterized by  high-pressure systems with  associ-
ated fair  skies  interrupted every 3 to 4 days  by the passage of synoptic-scale
low-pressure  storm  systems.   Air masses  determining  Great  Lakes weather  are of
Pacific  origin  about  30 percent of the time during  summer  and 75 percent of the
time during winter.   Gulf of Mexico air  masses  constitute  10 to 40 percent of
the  summer weather,  but seldom penetrate as far  north  as the upper lakes in
winter  (Phillips and McCulloch, 1972) .    Arctic  air  outbreaks during winter are
common over the basin.

     The Great  Lakes  act as a vast reservoir  for the storage of heat energy and
its  subsequent  exchange with the atmosphere.   During fall and  winter,  intense
heat and momentum transfers occur and the Great  Lakes'  interaction with, and
influence  on,  synoptic and mesoscale weather  are greatest.   Cold,  dry  Arctic air
moving across the warm water of the Lakes triggers  numerous  phenomena  such as
increased  cloudiness,  convective precipitation,  increased down-wind air  tempera-
ture,  and  intensification of low-pressure systems due  to large  inputs  of heat
and moisture.

     Air mass modification occurs rapidly.    Phillips (1972)  found that during
cold air outbreaks  over Lake Ontario more than half  the total  temperature modi-
fication occurs  over  the first 3 km of water.   The  degree of modification is a
function of  the initial air-water  temperature  difference and the length  of time
the air  is  over  the  water.   Phillips's results  also  show that,  in the  lowest 15
Q  ,  the maximum modification usually does not exceed 55  percent of the  total pos-
sible modification.    (Total modification is when the air warms to the  same tem-
perature as the water.) A mesoscale  consequence of  the addition of heat energy
and moisture  is the creation of  a  local  system with cyclonic vorticity,  a  low-
pressure trough  that  in terms of pressure translates  into  a  deficit of up to 6
mb over  the lake area (Petterssen  and  Calabrese, 1959).

     With  upward  heat  flux,  a high intensity  of turbulence in  the  atmospheric
boundary layer  is produced by buoyancy.  This increased vertical exchange of
momentum during  winter results in increased wind speeds in the surface layer
and, presumably,  a  decrease of speed in  the upper  layers.    It  has been estab-
lished that  overwater  wind speed is indeed  a  function of  the difference  between
land air temperature and water  temperature,  which is a  measure of the  a^mos-
phere's stability.   For example,  with the water 8C warmer than the  air  tempera-
ture,  Richards  et al.   (1966)  found that  the overwater wind  speed  over  the  lower
Great Lakes was  about  twice that of the  upwind  land  station.   The mean monthly
thermal  stability  values ,(T.. - T     .) using Alpena and Saginaw,  Mich., air
'temperatures and 15 m water temperatures from nearby moorings show the charac-
teristic pattern  (Fig.  3).   Very unstable conditions exist  from November through
March,  implying  that  for this period the wind speeds over Lake Huron are prob-
ably about twice  those recorded at nearby land  stations.  During April the  air
becomes  increasingly  warmer and hence  is neutral to slightly stable, while  con-
ditions  during  May  are extremely stable.

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 Figure  3.   Comparison of  air  tempera-
   ture measurements at meteorological
   stations near  the west coast of Lake
   Huron and water  temperatures at IS m
   depth at nearby  current meter moor-
   ings during  winter 1974-75.
                                                          SAGINAW-106 (t5m)
-ALPENA-109 15m
                                                           J    F    M
                                                          MONTH OF YEAR
     During April  and  May the cold water rapidly cools  the  air  above by conduc-
tion and  a  cold dome of extremely stable air extends  100  m  to occasionally 1500
m above the lake  surface  (Lyons,  1970) .   The conduction inversion that develops
is generally  less than 100 m deep and strengths of 25C/100 m have  been reported
 (Bellaire,  1965). The cold air dome  and inversion effectively  shield the lake
from surrounding  atmospheric  influences.  Vertical exchange of  momentum is dras-
tically reduced with the  results  that cumulus  clouds  are  absent over the water
due to subsidence,  thunderstorms  are  suppressed, and  most important for this
study,  wind speed and consequently waves and currents  are dramatically reduced.
This mesoscale anticyclone appears to be a  separate feature of  each of the Great
Lakes  (Strong,  1972)  and  is more pronounced over large, deep  lakes  like Lake
Huron.
     Wind data  from five stations, Alpena  and  Saginaw,  Mich., and  Goderich,
Bruce Ontario Hydro,  and Southampton, Ont, , were used  to  define the wind field
over the lake.  The  mean monthly wind speeds for November  1974  through May
1975 show that  speeds at most stations peaked  in January,  dropped  off slightly
through April,  then  decreased  markedly  in May  (Fig. 4).   The  decrease in May
was due to  the  cold air over the lake,  which spilled over the nearshore land
area, and the general decrease  in  the  synoptic pressure gradients.  Note that
Saginaw, farthest  from  the  lake  and probably out of the cold  air influence,
experienced a lesser speed  decrease.

     Wind run roses  for  the five recording  stations,  expressed  as  a percentage
of the  total  wind  flow past each anemometer during the  analysis interval,  are
shown on all  subsequent  15  m current  maps.   The wind roses  are  displayed accord-
ing to  meteorological convention,  i.e.,   the direction  is  that from which the

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    10
  -. 8
   a
   u
   a
   (A
   a
     
            	 BRUCE
            	SAGINAW
            	GODERICH
            	SOUTHAMPTON
            ___ ALPENA
                   I     I    I
          0   J    F    M
             MONTH OF YEAR
Figure  4.   Monthly mean  wind  speeds
  measured at five me teoicological
  stations about  the  perimeter of
  Lake  Huron.
 wind  blows.   The  prevailing directions,  southwest through  northwest,  and mean
 scalar speeds for the period  of about 4ms,  "Indicate that the November 1974
 through  May  1975  wind regime was near  "normal."   No attempt has been made to
 adjust  the measured  land winds to simulate  overwater  conditions.   It must be
 kept  in  mind that instrument location  and  exposure  can cause variations in the
 measured winds  and that overwater winds  are  dependent  on thermal stability as
 described by Richards et al.  (1966)  and  others.
                        3.2 Water  Temperature  Structure

       A comprehensive study describing water  temperatures  in the Great Lakes  was
 published  by Millar (1952).  who  constructed  monthly  temperature charts for each
 of  the lakes during 1935 to 1941 using  temperature data  from ships'  intakes.
 Data  from  the navigation months were extrapolated to  obtain means  for the win-
 ter months.   Measurements  of  winter temperatures were  limited  to the surface
 layer using the airborne  radiation  thermometer  (ART)  technique  (Richards  et  al.,
 1969).   Satellites  also provided infrared data.   However,  both methods are lim-
 ited  to cloudless  days and measure  only  surface  temperature.   Temperature data
 obtained during the 1974-75 Lake Huron winter study  provided the first  contin-
 uous  large-scale synoptic  picture of winter  temperatures in Lake Huron.

       During the period of study,  the winter  temperature structure was essen-
tially  isothermal  at all  stations (Fig.   5), indicating that mixing was taking
 place throughout the water column.  Though the  shallowest  depth at which  water
 temperature measurements  were  taken was at 15 m,  bathythermograph  results  from
 Lake  Michigan show that the water temperature in winter  is uniform from the
 surface to at least 120  m (FWPCA, 1967)  .   There  are  periods during calm,  cold
 conditions  when a  shallow reverse thermocline  forms,  but  such  stratification
 is  readily destroyed by wind and turbulence.   A winter thermocline of unspeci-
 fied  magnitude at  a depth of about  180  m was observed in  Lake Michigan,  with
 indications of large-amplitude internal waves on the  thermocline  (FWPCA, 1967).
                                          8

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  Figure 5.  Monthly mean water tempera-
     tures  from Lake Huron's  deep north-
     eastern basin  (mooring 113), the
     northern part of the lake offAlpena}
    f4ioh. (moorina 109), and  the south-
     ern end (mooring 101),
                                                         D    J     F    M
                                                             MONTH OF YEAR
  In Lake Huron  a  temperature  difference  of up to 0,8C was observed  between  25
  and 136 m depths in  the  deep northeastern basin in March, but it  is  doubtful
  that this weak temperature gradient  would result in  significant internal  wave
  development.

       Some spatial characteristics  of  the observed Lake Huron  winter temperature
  field are shown in Figure 5.    The  nearshore areas (moorings 101 and 109)  cooled
  rapidly,  with  the minimum temperature of 0.2C first  occurring in  middle-to-late
  February, while the  northeastern basin did not  reach its minimum of 1.5 C until
  early April.   The monthly cooling  rate  in the northern basin  was  about 1 C  per
  month from December  through  March,  while the rate was 1.6C per month  in  the
  southern  basin.   The largest  horizontal  temperature  gradient was  in  February,
  when the nearshore areas had cooled to near zero and the mid-lake region  was
  still about  3C.   It was also the  month with the coldest air  temperatures and
  maximum ice  cover.   Figure 6  shows  the  isotherm pattern  for  the  upper  15  m.
  Lack of data in the  eastern  part of the lake reguired some  suppositions  (given
  as dashed lines).   Other winter  months  showed basically  the same  isotherm pat-
  tern,  although the horizontal  gradient  was  less,  and were similar to ART results
  (Richards et al.,  1969).

       The winter thermal  structure  is  established and maintained through the
  interaction of several processes.   The coldest  air  temperatures  are associated
  with westerly and northwesterly  winds and so the greatest heat flux  takes place
within  the  first 10-20 km lakeward  from the west  shore.   When the shallow near-
  shore water cools to near zero,  ice formation retards wind  generated mixing,
  prevents  conductive  heat flux  with  the  air,  and reduces  radiational  heating.
  A  winter thermal  bar, a  sharply  defined boundary between  the  near-zero inshore
  water and 2C offshore water,  was  observed  about 16  km offshore in  Lake Michigan
  from bathythermograph surveys (FWPCA, 1967).   Although bathythermograph surveys

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            . Marie
                   LAKE HURON
           'Bay City

        MICHIGAN
      SCALE IN KILOMETERS
      0 20  40 60  80 100
                                         Figure 6.  Monthly mean water  tempera-
                                            tures (C) at IB m depth  during
                                            February 1975 in Lake  Huron.  Dis-
                                            tributions in the eastern parts of
                                            the  lake are assumed,  but ice was
                                           present  along the east  coast,  in-
                                            dicating  the presence of near 0C
were not performed  during  the  Lake Huron winter study, the  monthly  temperatures
from inshore  and  midlake locations  and  the  extent  of the ice  formation  suggests
that a  winter  thermal  bar  probably exists in Lake Huron also,  at  least  around
the northern basin.  The  sharpness of the thermal discontinuity and  its  effec-
tiveness in  inhibiting  mixing  between the two water masses  needs  further  clari-
fication.

     The shallower  southern  basin cools most rapidly  through  conduction  and
convection and  the  mid-lake  ridge inhibits subsurface water movement  between
the two basins.   A  comparison  of temperatures to the north,  south, and on  the
ridge  (moorings 116, 119,  and  118,  respectively,  in Fig.  7)  shows that the
northern basin  was  cooler  until  mid-January  and thereafter warmer through April.
The temperature difference reached a maximum of 1,6C in March.   During  January
and February the  ridge  temperature (at  mooring 118)  was colder than  either
basin,  which is consistent with  previous  data observed in this area.   Individ-
ual ART surveys in  winter  and  spring showed  the isotherms following  the  general
isobaths of the ridge;   transparency measurements  showed a tongue  of  more  turbid
water extending northwestward  into the lake  (Ayers  et al.,  1956), and satellite
imagery showed turbid  plumes meandering lakeward in the ridge area, with  the
water over  the ridge warmer  than either  basin during the summer warming  period
 (Strong, 1974). Apparently a part  of the  northward flow along the eastern
shore is deflected  lakeward by the  ridge,  resulting in more turbid  water over
the ridge  and  cooler or warmer temperatures,  depending on the season.
                                        10

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   Figure  7.   Water temperature distri-
     bution across the mid-lake ridge.
     Mooriny 116  was  just north of  the
     r'idf-e in, the southern ?art of the
     deep northeastern basin,  mooring
     118 'Jas on the  ridge,  and mooring
     119 Das just south  of the ridae
     in the  southern basin.
o
D
lu
(E

i
sn
LU
DC
lu
I
                                                        k119 (50 m)
ITS (43
                                                        D    J    f    M    A
                                                           MONTH OF YEAR
                   3.3  Seasonal and Monthly  Current  Patterns

     Currents  observed  during  the winter surveys are  summarized  as monthly and
seasonal current roses  in  Appendix A.    The  current  roses present the distribu-
tion of  current  run,  expressed as a percentage of the total  water transport
past each  current  meter suspended in the water column,  in a  fashion analogous
to our presentation  of  wind statistics.   The  current  roses  are draw" to show
the percentage of  flow past each  meter  toward each  octant in the oceanographic
preference, while  the wind run roses retain their usual  presentation in the
direction  from which the wind  is  blowing.    There are,  of course, many alterna-
tive techniques  for  the presentation of flow  statistics.   The  choice made here
has the  advantage  that  it  is easily interpreted  visually to give patterns  of
dominant water transport in addition to some  indication  of the variability of
current  flow.   The disadvantage of this sort  of presentation is  the  absence of
a suitable display of  the  lake-scale distribution of  current speeds.   To  display
representative current  speeds for lake currents, we will include several  charts
of resultant current vectors.

3.3.1 November 1974
     The winter  current  studies started in November  and  current  patterns pre-
sented represent only  the  latter  third of the month.   Figures A.la-d  show  the
current and wind roses for  this period.   Each  level  of observation is' show" on
a separate chart and it  should  be noted that several current meters  used at  the
25 m level were just 2  m off the  bottom (those at the mouth of Saginaw Bay and
                                      11

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at the extreme  southern  end of the lake),   as  were  many of the current meters
shown at  the  50 m level  about the perimeter of  the lake and on the mid-lake
ridge.    I"  general,  current meters at the  25  and 50  m levels showed flow charac-
teristics very  similar  to shallower current meters on the same mooring for the
duration  of the winter  season.  Therefore,  current meters near the bottom at 25
and 50 m were usually still very much within  the upper level flow regime during
winter in Lake  Huron  and are presented as   such.  Bottom currents at 2 m off the
lake floor  are  shown  only in much deeper water.

     November winds  prevailed from the  southwest  quadrant at meteorological
stations  in the southern half of the Lake  Huron basin,  while Alpena recorded a
higher percentage  of  wind from the north-northwest.   Lake water temperatures
were nearly uniform throughout the upper SO m,  averaging a little less than  6C
in the northern half  of  the lake and just  over  7C in the southern half of the
lake.   Along  the Michigan coast a  dominant southward flow characterized the
circulation.   This steady southward flow ran  parallel to the bathymetry and
was present from surface to bottom with unchanging  steadiness.   Not all of the
current  meter moorings were deployed in the eastern  part of the lake, but  re-
porting  stations  showed  a return northward  flow along the east coast closing
the circulation to form one  large cyclonic cell.   The pattern of flow was
especially  steady  and persistent about the perimeter  of the  lake,  with only
mooring  113 in  the center of  Lake Huron's  northern reaches showing much varia-
bility.    Here the  resultant flow was northward  at  all levels.   East-southeast-
ward flow at  the 50 m level at mooring  112 persisted for the entire winter sea-
son.   Mooring 112  was placed  on a  ridge-like  structure protruding eastward into
the lake  basin  from the  vicinity of Cove Island.   The lake bottom is deeper
both north  and  south  of  the station,  and the  50 m  level flow was nearly paral-
lel with the  local bathymetry.

     The  coherent  pattern of  lake-scale circulation  illuminated  by the Novem-
ber data  is unusual  in  comparison  with  earlier reported surveys of  currents  i*1
Lake Huron  during summer  (cf.,  Sloss and Saylor, 1975).   The consistent pattern
of lake-scale  flow,  as  observed especially along the  western coast of the lake,
is attributed  to the  improved instrumentation used in the surveys  and not to
any fundamental  changes  in the character of Lake Huron currents.
3.3.2 December  1974
     December  winds were predominantly  southwesterly over the entire  lake basin
 (Fig.  A.2a).   Water temperature was nearly  isothermal  throughout the lake,
averaging just  over 4C.   Currents observed  during  December  are shown  in  Figures
A.2a-d.   Southward  flow along the west  coast  of  Lake Huron south of Alpena  con-
tinued to be the  dominant feature of lake circulation.   Return  flow along  the
eastern shore  was  not as persistent as  observed  in  November,  although  the  east-
ern shore current meters and'most of the mid-lake stations  exhibited a general
northerly drift.   Mooring 118 on  the  mid-lake ridge showed northwesterly  flow
at both 25  and 50 m,  while at mooring 119  south  of  the ridge the flow  below 50
m was  northerly.   North of the ridge the  current meters  at 50 m and near  the
bottom at mooring 116 exhibited southeasterly flow,  a  pattern that persisted
throughout  the  winter.

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     At the  mouth  of Saginaw Bay,  current  meters  at 15 and 25 m  depth  indicated
a  clockwise  flow pattern.   This  is  consistent  with the work of Danek and  Saylor
(1976), who  found  that a clockwise  eddy  occupied  the  outer reaches of  the  bay
during  southwest wind conditions, with.the core of  southerly  flow along the
west coast of  Lake Huron pushed lakeward.   On  the other hand, northeasterly
wind caused  a  part of the Lake Huron  flow  to  sweep in a counterclockwise loop
through the  outer  reaches  of the bay,  exiting  the bay in eastward flow just
north  of  the Michigan thumb.
3.3.3  January  1975

     Southwesterly wind flow in January (Fig.  A.3a)  was  similar to the wind
distribution observed  in December,   although  the  mean wind speed was greater,
as  January  recorded the highest mean wind  speed  during the 1974-75 winter  sea-
son.   Cooling  of  the lake's water mass  resulted  in nearshore water  temperatures
averaging about 2C, while over the  deep northeastern basin ^water temperature
averaged  a  little  less  than 4C.   Current  flow during the month is  summarized
in  Figures  A.3a-d.   The circulation was  essentially  unchanged from December.
Southward flow along the east coast of  Lake  Huron  continued to be the dominant
feature in  the  lake.   Flow along the mid-lake  ridge  retained the  characteristics
observed  the previous  month,  with northwestward  movement  on the ridge itself
and  a  southeastward return in deeper water to  the  north along the southern mar-
gin  of the  deep northeastern basin.   The clockwise eddy at the mouth  of  Saginaw
Bay  intensified from the December pattern, and the southerly  coastal  flow  mi-
grated lakeward far  enough  for  mooring  106 to  be influenced by this  localized
cell of circulation.
3.3.4 February  1975

     In  February,  winds  shifted to a more  westerly direction with more  episodes
of wind  with  a  northerly component.   Continued  cooling  of lake water near  the
coasts caused water at nearly 0C to encircle  a warmer  core  of denser water
centered over the  deep northeastern lake basin.   Currents,  shown in  Figures A. 4
a-d,  were  strongly  cyclonic.   Currents  along the Michigan coast were almost
exclusively southward,  and northward return  flow along  the Ontario coast was
very steady in  the  southern basin.  Flow  through the outer reaches of  Saginaw
Bay was  in one  large counterclockwise loop.

     We note  that  with the westerly wind  of  February,  flow at mooring  118  on
the mid-lake  ridge  lost its  strong  northwestward character,  changing to  south-
eastward flow at 25  m and  bimodal at 50 m.   The flow remained nearly parallel
with the bathymetry,  though,  as it did  throughout  the  season.   North of  the
ridge,  mooring  116  continued to record  southeastward  flow at deeper  levels  in
the northeastern basin  of  the lake.   South of  the  ridge,  southeastward  flow at
25 m at  mooring 119 was accompanied by  more  northward flow components  deeper
in the water column.
                                        13

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3.3.5 March  1975

     The water  temperature  patterns of February continued  into  March,  as cold,
near 0C water  surrounded slightly warmer water  centered over the deep  north-
eastern basin.   This  warmer water  had  cooled  somewhat from February,  however,
and averaged  about  2C  for  the month.  Wind over  the Lake Huron basin prevailed
from the  northwesterly quadrant  (Fig.  A.5a).   Currents  observed during  March
are shown  in Figures A.5a-d.  Flow throughout  the lake  basin was very strongly
cyclonic,  almost  exclusively southward along the  west shore,  and northward  along
the southeast shore.   Flow toward  the  southeast  along the mid-lake ridge at 50
m  (mooring 118)  conformed with bathymetric constraints  and was  similar  to the
February currents.   Southeastward  flow at mooring 112 at 50 m still persisted
as it had  all winter,  while mooring 110 at 50  m  was now dominantly southeast-
ward also.
3.3.6 April  1975

     April winds  were northwesterly, very  similar  to the wind distribution  ob-
served in March.   Currents during April  (Figs. A.6a-d)  were very similar to
those during March,  characterized by very  steady  southward flow along the west
shore of  the  lake and northward return flow  along  the east shore south  of Clark
Point.   A  steady  counterclockwise flushing of  Lake  Huron water through  the
outer reaches of  Saginaw Bay  was also prominent.   The start of spring warming
near the  coasts of the lake established an almost  isothermal  lake during April,
with monthly averaged water temperatures  varying no  more than 1C throughout
the basin.
3.3.7 May  1975

     The Canadian  current meters were removed  in  early May,  while  the  United
States meters were  removed in late May.    Therefore  only the  west shore  of  the
lake is  covered in Figures A, 7a-c, but data from  these meters show a remark-
able change in  the  character  of Lake Huron current  flow.   As noted earlier,
intense  atmospheric stability over the  cold  lake  surface in May  was  associated
with reduced wind  speeds  at stations along the perimeter  of  the lake.   This
sheltering of the  lake surface from strong wind  stress resulted in a catas-
trophic  decrease in the kinetic energy  of the  water mass and, inferred  from  the
observed current patterns, the  loss of  an organized pattern of current  flow  in
the lake.  The  southward  flow along the  lake's  west coast,  as observed  in  all
earlier  months,  was absent although a counterclockwise flow  through  the outer
parts of Saginaw Bay was  still apparent.  The  warming of nearshore water  that
started  in April continued through May  so that  at the time of current meter
removal,  shorebound  water as warm   as   8  to  10C  had reached offshore to the  15
m level  at several  of the current meter  stations.   The neat-shore warming  and
concomitant establishment of  significant  horizontal temperature  gradients  does
not in  itself,  however, prove  the  existence  of characteristic  circulation  pat-
terns in the  absence of significant wind stress.
                                       14

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3.3.8 Winter  Circulation

     Wind and  current  roses  for the entire winter  season  are  shown in Figures
A.8a-d.  Only  those  meters  operating a significant part of  the  season are
included.    The  patterns  show that there was  clearly  a  dominant,  or character-
istic,  current  flow during the 1974-75  winter season in Lake Huron.   Southward
flow along  the  lake's  west  coast was very steady  and extended  from Alpena to
the southernmost end of  the  lake.   The mouth  of  Saginaw Bay exhibited two pat-
terns of circulation,  either a counterclockwise loop of Lake  Huron water flow-
ing through the  outer  bay during northerly wind,   or  a  clockwise  eddy in the
outer bay during  southwesterly  wind.    Return  northward flow along the east
coast of the  lake  was  not as clearly defined  except  in the  region south of
Clark Point.   Unfortunately,  many of the  current  meters in  the important coastal
zone in the northeastern part of the lake  failed to return useable current
records.

     To indicate  current speeds associated with  the  winter  circulation,  resul-
tant current  vectors for the season are shown in  Figure 8.   The  highest cur-
rent speeds wet-e observed close to the coast, with  speeds decreasing toward
the center of the basin.   The strongest resultant  currents  were  associated
with the southward  flow  along the lake's west coast, with the  remainder  of the
lake exhibiting  a  less intense northerly drift forming one  large cyclonic cell
of circulation.   Flow  along  the mid-lake ridge was  usually  parallel with the
bathymetry,  either  northwesterly or southeasterly,  although the  vector resul-
tant current was northward.   Just north of the ridge,  currents  at deeper levels
at mooring  116  were  southeasterly along the  southern flank  of  the deep north-
eastern lake basin.

     Mooring 111 between Georgian Bay and Lake Huron has  not  been discussed in
connection with  lake circulation as it was placed in a north-to-south trending
channel separated  from the  lake by intervening shallower  depths.   The resultant
current vector  for  the season indicates an inflow of water  to  Georgian Bay at
the 25 m level,  however,  which was probably balanced by a return flow to Lake
Huron at deeper depths  as reported during summer (Sloss and Saylor, 1975).
The 50 m level  at  mooring 109 was  also poorly exposed  and probably exhibited
local effects not  closely tuned to whole lake patterns because of the shoal
water that protruded eastward in the lake just north of North  Point at Alpena.
 (Depths shallower that  10 moccur south-southeast of this mooring.)

     To get an  idea of the volume  of water transported about  the lake by the
resultant circulation,   we computed  the  south-southeastward  volume transport
across the  section of the lake between moorings'103 arid"104, just east ot
Saginaw Bay.   The  lake bottom between these two  stations  is flat,  with an aver-
age depth of about 50  m.   We know the  velocity distribution in  the upper 25 m
and could reasonably assume  a conservative velocity  profile as  linearly decreas-
ing from the 25  m  level  to no flow at the lake bottom.   The resulting volume
flux was about  40,000  m /s,  or  roughly eight times the long-term average dis-
charge of  the St.  Clair River.   Throughout the survey  interval  (about 180 days),
this meant  that about  625 'km of  water  was transported southward through the
section.. _This  is  nearly one-fifth of  the total  water  volume  of  Lake Huron
 (3,500 km }.  Most  of  this  water must  have returned  northward  in the eastern
parts of the lake basin.   This implies that  the  bulk of the lake's water mass

                                       15

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     ault Ste. Marie
                 LAKE HURON
                                Point
                                Clark;
           'Bay City
        MiCHIGA  N
                                4MLGode-
                           ..   r-
M *
                      Huron'
                                         Figure  8.   vector  resultant current
                                           flows in  Lake Huron  during winter
                                           1974-75,  The depth fmJofeach
                                           current velocity measurement is
                                           shown with the current vector.
is certainly in a well-mixed condition.   Short-term  transports  through the
section,  both southward and northward, were  of  course  much greater,  accelerat-
ing the mixing of lake water.


                            3.4  Episode Analysis

     Circulation patterns  depicted by the seasonal and monthly current maps are
the integrated result of all the  wind stress fluctuations  and accompanying cur-
rents that occurred during that particular time  period.   It 1S als instructive
to examine the current  response  and circulation patterns  that develop during
short-term episodes of steady wind  stress.

     Synoptic weather systems pass  over the  Great  Lakes  region  rather  quickly;
therefore times when winds are  directionally steady  are  usually limited to
several days duration.  The  episodes  discussed  in  the  following sections were
selected on the basis of wind  data,  primarily from Saginaw and Alpena.
periods of 3 days  or  longer with  nearly  steady  wind  direction and mean wind
                                       16

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speeds of 5 m s    or  greater are presented.  The  wind  and current data are con-
current;  lag time  to  allow for current response was  not applied because the
periods of  steady  wind  stress did not  always exactly coincide between stations
and current response  varies  with several factors  such  as  location and depth.
This does not present a serious problem since  there  are normally generation,
steady state,  and  decay epochs associated with significant  storms  so that any
residual currents  from  a  previous regime are soon overpowered by currents gen-
erated during the  selected episode.   Data  are  presented in  the same form as in
the previous section  and  are contained in Appendix B.
3.4.1 20-22 November  1974
     A deepening  low-pressure center moved  across the northern states and
passed over Lake  Huron  on  20  November.    Strong  cyclonic  circulation over the
northeast United  States  continued as the center migrated  across New York on
the 21st.  Winds  over  the  lakes were westerly to  northerly  during the 3-day
period (20-22 November),  with mean speeds along the  perimeter  of Lake Huron of
5 to 7 m s  .    Not  all the current meters had been  deployed,  but large-scale
cyclonic circulation in the lake with a  counterclockwise  loop  through the outer
portion  of Saginaw  Bay is evident in charts (Figs.  B.la-d)  for that date.   The
current penetrates  to  at least 50 m with little change in direction except at
mooring 112,  where  the  current is almost exclusively northwesterly  at  15 m,
northerly at 25 in,  and easterly at 50 m.  As pointed out  in the discussion of
the monthly currents,  mooring 112 was positioned on  a ridge and the 50 m depth
flow paralleled the bathymetry  during  the  entire winter. Although the shallow
meters on moorings  110  and 112  failed shortly after  this  episode,  the currents
are indicative  of what  can be expected during the rest of the  winter when there
is a northwest  wind.
3.4.2  30 November-2 December 1974
     Northeasterly winds  5  to 8 m s    across  Lake  Huron 30 November through 2
December resulted  from a deep  low-pressure  system  that developed over the  south-
western states  and migrated across Tennessee  and Virginia.   Currents during
these  3 days  (Figs.  B.2a-d) showed a  clockwise gyre in the southern part of the
lake.   The  counterclockwise looping through the outer  region  of Saginaw Bay was
consistent  with patterns observed by Danek and Saylor  (1976).  There was consid-
erable shear in  the  bay.   Mooring 108  showed  the water moving into the bay at
the 15 m level  with  the wind stress;  however,   the  outflow speed at 25 m was
about  twice that of  the inflow and caused a net eastward  flow past the site.
The current speed  at mooring 105 was about  60  percent  higher  at the 25 m  depth
than at 15 m.   Flow  at the  15 m depth  at  mooring  109  was northwesterly,  a  typi-
cal response to  northeast winds and not unexpected  because of the shoal water
south  and east  of  the mooring.   Mooring 104  showed a   similar  response,  possibly
due to the  shape of  the shoreline.  Northwesterly  flow on the  shallower water
of the mid-lake  ridge  (mooring 118) was just  exactly  opposite to the flow  of
water  in the deeper  water north and south of  the  ridge, a pattern  that  persisted
for much of the winter due to  the local  bathymetry.
                                       17

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3.4.3 26-29 December  1974

     A week of  west to southwest wind across Lake  Huron  dominated the weather
in late  December  as the eastern half of the United States  and Canada were under
the  influence of  a massive high-pressure system  centered over the southeastern
states.    Figures  B.3a-d show the general  cyclonic  flow pattern  that  existed in
Lake Huron during  the last 4  days  of the week-long episode  when the  current
patterns were well  established.   The currents were very  similar to those ob-
served for the  entire month of December, when  southwesterly winds prevailed.
Southward flow  along  the  lake's west coast was not quite as sharply  delineated
as it was during  more westerly and northwesterly wind  stresses,  and  a clock-
wise pattern of current flow  existed in the mouth  of Saginaw Bay.   Northwest-
ward flow along the crest  of  the mid-lake ridge was again  evident.
3.4.4  9-11  January 1975

     A  deep trough  extending from northwest Canada  to  Texas  developed over the
Plains  States.   The  center moved northeastward over  the  Midwest  and the Great
Lakes Basin on 11 January  and continued  into Canada.   The strong cyclonic air
flow resulted  in  7 m s   winds  from  the  southeast over the basin during the 3
days.    Lake circulation  was essentially anticyclonic, a  rare  event  in Lake
Huron since  southeast  winds are generally  less  intense  with shorter (* 2 days)
duration  (Figs.  B.4a-d).   The pattern of flow across  the mid-lake ridge as noted
in  the  northeasterly wind  episode  was repeated,   with northwesterly currents
along the ridge  and  a southeasterly  return in deeper water  north and  south of
the ridge.   Clockwise  water transport in the mouth  of  Saginaw Bay was especially
clear in the  currents  at 25 m depth.

     This episode does demonstrate that given the  right  combination of wind
speed,  direction, and  duration,  the  characteristic  cyclonic lake circulation
can be  reversed.
3.4.5  11-14 January 1975

     The  deep  low continued into Canada.  Winds  remained about  8ms   ,  but
switched  to the  southwest as Lake Huron came  under  the  influence of the back-
side of the low.   The current pattern  (Figs.  B.5a-d) was  similar to the just
concluded  episode, but  several meters,  e.g.,  102,  104,  were  showing bidirec-
tional characteristics,  indicating that the current  was adjusting to the new
wind regime.   This adjustment was not  immediate,  however,  and showed that  con-
siderable time (on the order  of a day  OK two)  is required for the lake to  ad-
just its  current  flow to be in  harmony  with the  newly  applied wind stress  if
this stress does  not reinforce  an already existing  pattern  of flow.  A longer
episode of southwesterly wind presented earlier  showed  a substantially differ-
ent circulation  for  this wind direction.
 3.4.6  9-15  February 1975
      During the first 3 days  of the 9-15 February episode,  anticyclonic circu-
 lation prevailed over the Great Lake Basin from a weak  high.   On  the 12th, a

                                        18

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weak trough  over  the  Lakes area extended to the  Gulf  of Mexico.    Flat  pressure
gradients  prevailed during the remainder of the  period.   This episode  was
selected to  determine the effect  of ice-cover on current  patterns.   Ice, of
70- to 90-percent concentration,   extending  from Alpena to Port Huron and east-
ward to  moorings  103  and 101,  was observed on  12  February.   Winds were west  to
northwest  during  the  period so cyclonic lake  circulation  would be expected.
The current  rose map does show the  anticipated cyclonic  flow (Figs.  B.6a-d);
however,  the four moorings at  the head  of  Saginaw Bay were less  directional
than when  the  lake  was ice free and  current speeds  were much less.


3_._4._7 26 February-6 March 1975

     The Great Lakes  were under the  influence  of a low centered  in eastern
Canada during  26-29  February,  followed by another  closed  low north of  Lake
Huron on the 1st  of March.   This  low moved  over Quebec, while yet another  low
travelled  up the  East Coast,  causing  cyclonic  circulation over the East.   Lake
Huron therefore experienced  generally westerly  winds  for the 9-day period  with
mean speeds  up  to 9? m s    at Saginaw.   The  lake circulation  (Figs.  B.7a-d) was
again cyclonic, with  little  variation with depth except in  Saginaw Bay at  moor-
ing 108  where  the 15  m current was eastward and  the 25  m current more  westward.
Also the 50  m  currents at 109 were northwesterly,  opposite  to  that at 15 m, due
to the local bathymetry.   Temperatures  were between 0.0" and Q,BaC in  the  west-
ern half of  the lake, and 1.6' and 2.8C in the  eastern half.
3.4.8 1-8 April  1975

     A  cold  front  passed over Lake Huron on  1  April  and a deep upper trough
over the West  spawned a low-pressure center, which  passed over the lower  Great
Lakes on the 3rd.   This system moved over  New  England,  moved offshore,  and
filled  over  the  next  5  days.   The resulting  northwest  winds over Lake  Huron
produced the familiar  cyclonic  circulation pattern  (Figs.  B.8a-d),   Tempera-
tures illustrated  little spatial variation.  The minimum was 0.3C at mooring
102 and the  maximum was 1.8C at mooring 113 in  the  deep northern basin.   Cur-
rent flow during this important episode was  especially  steady  and gave an ex-
traordinary  picture  of  lake circulation during northwest wind  in those  areas
of the  lake  covered with functioning current meters.   An identical picture of
circulation,  and some idea of its persistence  is afforded by the current  roses
prepared for a  slightly different interval  of  time,  3-13 April,  shown  in
Figures B.9a-d.
3.4.9 3-7 May  1975

     This episode  was  selected to  determine  what circulation pattern  exists
during light,  variable  wind conditions.    The  atmospheric pressure  gradients
were small during most  of  the period,  interrupted  by  two weak lows moving  over
Lake Huron on  the  4th  and  6th.   The resulting winds for  the  5-day period were
north to  northeasterly at about 3ms.   A  conduction inversion,  discussed  in
a previous section,  undoubtedly formed over  the  lake,  reducing the overwater
                                        19

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wind stress.   The  Canadian moorings had been retrieved  so  only currents in the
western part of  the  lake  were measured.  The current pattern  (Figs.  B.lOa-c)
was somewhat disorganized.   Water flowed through  the  outer reaches of  Saginaw
Bay in  one  large counterclockwise loop as is characteristic  of the bay mouth
during  episodes  of northeast  wind.   Current directions  at  15 m were north and
northwest off  Alpena  (mooring 109)  and Harbor Beach  (mooring 102), respectively,
which must  have  been  in response to the northeasterly winds,  as  seen on other
occasions,   and the bathymetry,  even though the winds were  light.

     The circulation  pattern  was confused,  not unlike the  monthly histograms,
which showed considerable  transport variability.   As  pointed out  earlier, May
was a somewhat unique  month;  wind speeds decreased  considerably  around the
lake, and the  conduction  inversion that was present a large  percentage of the
time effectively decoupled the water from direct  wind  stress;  hence currents
were very weak and directionally variable.
                           3.5 Effects  of Ice Cover

     The  1974-75  winter  season saw the  first  successful  attempt at year-round
navigation on the  Great  Lakes  due in part to less than normal  ice  cover.   Air
temperatures well  above  normal through  early  January delayed significant ice
growth.   A month  of cold temperatures beginning  in  mid-January produced rapid
ice  growth with Lake Huron's maximum ice  cover  of 45 percent occurring  in mid-
February  (Leshkevich,  1976).   Warm temperatures  during the  last half of February
significantly decreased  the  amount of ice and,  although  March  and April air
temperatures were  well below normal,  the  number of  freezing degree-days was
not  sufficient  to  redevelop  significant  ice cover on the  lake.   The percentages
of lake  surface that can be expected to be ice  covered during  a mild,  normal,
and  severe winter  are about 40,  60, and  80 percent,  respectively,  for  Lake
Huron (Rondy, 1969) .

     In  an effort to describe qualitatively  the effect of  ice  cover  on circu-
lation patterns in  Lake  Huron,  currents during the 9-15  February 1975 maximum
ice  period were compared with currents  of the 26 February-6 March 1975 period,
which had similar  wind conditions but little ice  cover.   Results from Side
Looking  Airborne  Radar (SIAR)  surveys on 8,   10-13,  and 16  February revealed the
basic features  of  ice coverage at its maximum development.   Figure 9 shows a
SLAR image on  12  February 1976.   Winds  during the ice  period were light to
moderate westerly  with the  exception of light easterly winds on the llth and
15th.  A 10  to  20  km-wide band of  close  pack ice (70-90 percent  ice  cotfer)
along the western  shore  of the lake persisted through  the period,  while the
southern  portion  was almost totally covered.   The eastern shore showed a 5
km-wide  ice  pack  along the  shore  up to  at least  Clark  Point.    Both shores re-
sponded  somewhat  to winds and cold temperatures.   The  western  band moved off-
 shore  somewhat during stronger westerly winds with new ice  forming behind it,
while the eastern  band became more compact.   The opposite  occurred during east-
erly winds.   Even  though the wind was westerly  during  most  of   the period,  no
evidence  of  ice moving across the lake  was seen.   Only shifting of the  outer
boundary  and the  degree  of compactness  was noted.   The cyclonic character of
the  circulation was evidenced by  strong  shear zones  and lakeward extention of

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                                     Figure 9.    Side-Looking  Airborne Radar
                                       image showing  the  ice  cover on western
                                       Lake Huron  on 12 February  1975.   White
                                       areas  indicate edges and cracks in the
                                       ice.
ice near Alpena  and the head of Saginaw Bay  and  by the northward movement of
pack ice along the  Ontario  shore.   A  combination  of warm air temperatures and
wind and current  activity broke  up the ice into  smaller  floes,  so that by 16
February the amount  of  ice  decreased and only a 5  to  10  km band of floe ice
remained on the western half of  Lake Huron.

     Figures 10  and 11  show the resultant speed  and direction for each meter
and the average  ice  cover  for the two  episodes  (Leshkevich,  1976) .   Currents
displayed in histogram  form  for  the  two periods are  included in Appendix B.
Current direction and magnitude  appeared unaffected in most  parts of the lake
except off the Saginaw  Bay  area,  where  the  resultant speeds  were near zero
during the ice period and  5-17  cm s     at the  end  of February.   Particularly
obvious was the  greatly reduced  speed at mooring  104  off Point  aux Barques.
This particular  site was in an area of  intense currents.   The resultant speeds
at 15  and  25 m were^.3 and  0.5  cm s    respectively,  during ice cover and
10.3 and 16.7 cm  s    during the comparison  period. Offshore currents north
(mooring 107) and south (mooring 102)  of Saginaw  Bay showed  little change in
speed  or direction.   A  decrease'in mean monthly kinetic  energy  of the lake in
February was attributable in part  to ice growth.

     The only empirical study of currents in  a large lake with partial ice
cover  that is known to  the  authors was  reported  by Palmer and Izatt (1972).
                                        21

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            LAKE HURON
      Bay Cily

   MICHIGAN
 SCALE IN KILOMETERS
 o  20 40 So ao 100   port
                Huron
                                    Figure  iO.   Sector resultant  current
                                      flews in Lake  Huron during 9-15
                                      February 1975.   The average  ice
                                      cover during the interval is shoun
                                      by the broken line.
'Sault Ste. Mane
             LAKE HURON
Hl I  I I   ,
0 1  4 91625
  cm s"1    
      'Bay 'City

   MICHIGAN

 0  20 40  GO 80 TOO
                              o
                Hurom
                                     Figure 11.   Vector  resultant  current
                                       flows in Lake Huron during 26 Feb-
                                       ruary-6 March 1975.   The average
                                       ice cover during the interval is
                                       shown by the broken line.
                                   22

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Their results  from  one  current meter 0.8 km  offshore  at  Nanticoke,  Lake Erie,
indicate that  during  the  ice formation period,  with  ice  extending 0.5  km
beyond the meter site,  the currents did  not  vary appreciably from those when
the lake was ice free.  When the ice cover extended  1.5  km beyond the  mooring
location,   currents  were weak,  with long periods  of no movement.   Also  no  sig-
nificant energy was  detected at the free oscillation  periods  as  there  was  dur-
ing the ice  formation period.   Palmer and Izatt  gave  no  information on the
amount of  ice  cover  on  the whole lake so that the surface area available  for
direct wind  stress  forcing  is  not known.   Arctic ice  investigations have  con-
centrated  on determining  the momentum exchange  from  the  atmosphere through the
ice into the oceanic  boundary layer and ice-water  stress.   Sheng and Lick  (1973)
calculated numerically  the  steady-state  wind-driven currents  in  Lake Erie  when
the eastern  third  or  western third of the lake  was ice covered and compared
these results  with  those  calculated for  ice-free conditions.   The  comparison
basically  showed that currents under the ice  were  weak except near the ice
boundary,   where velocities  were comparable to  ice-free conditions.

     The presented  evidence indicates  that ice  on  the western portion  of  Lake
Huron does result  in  dramatic current speed  decreases in areas,  such as the
head of Saginaw Bay,  where  the meters  are far  enough  removed from the  open
water to prevent  significant lateral momentum  transfer.   There may be  little or
no change  in the  observed current velocity north and  south of the Bay  because
the meters were not always within the ice-cover  area  or  were very near the ice
boundary.   Distribution of  ice cover is  controlled by the general cyclonic lake
circulation,  forcing  it  southward along the  western  side and northward along
the east coast.   Ice  forced into midlake, as  occurs  north of Point Clark  and
the Alpena area,  is melted by the higher temperature  of  the water.

     The 1974-75  winter  season was mild, with little  ice cover,  and  we can only
speculate  on what  effects greater amounts of  ice would have on the current pat-
tern in Lake Huron.   Obviously as the ice cover  increases,  the area  upon  which
wind stress  can act  decreases  and the kinetic  energy  of  the lake will  decrease.
As the ice cover  approaches the  severe classification as in 1967  (80 percent
coverage),  the currents  would probably be greatly diminished.


     3.6 The Annual Cycle  of  the Variation of Current Speeds with Depth

     There have been few studies  of  currents and concomitant water  temperature
distributions  during  winter in the Great Lakes.   It   is  therefore  instructive to
look at the  distribution  of current speeds  throughout the water column as  winter
progresses and to compare  this  distribution with what is  known  during other sea-
sons of the year.    Figure 12 presents mean  monthly current speeds observed at
all moorings at the  four  levels of measurement  in  the water column.  Mean cur-
rent speeds  in November  exhibited considerable  variation with depth, with  speeds
highest at the 15 m  level and decreasing monotonically with depth.   The Novem-
ber currents were  associated with the last  vestiges   of  summer density  stratifi-
cation.   December mean  currents decreased from  November  values  at the  15  and
25 m levels  and increased at 50 m and near the  bottom.    There were  no  signifi-
cant differences  in  current speeds in the upper  50 to of  the water  column  in
December,   establishing  a  pattern of flow variation with  depth that  continued
for the remainder  of the winter  months  in  nearly isothermal water.

                                       23

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                5  m
                25m
               50m
               2 m off bottom
                                          Figure  12.   Monthly mean  current
                                            speeds at  the  four levels of meas-
                                            urement in Lake Huron  during winter
                                            1374-75.   Scalar mean  speeds  were
                                            averaged  for all  operating current
                                            meters at each depth.
               j     F    M
              MONTH  OF YEAR
     Mean monthly  wind  speeds at five  stations  scattered  about the perimeter
of Lake Huron were  shown  in  Figure  4.   The  average  winds  were nearly the same
at all  stations  during  November and December, peaked  at all stations in January,
and then exhibited  a  rather  uniform decrease through  the  winter  and into April.
The station most representative of overwater wind speed was the Bruce Ontario
Hydro installation at Douglas  Point,  Ont.,  as its  location on the  shoreline
gives good exposure to  the prevailing westerly winds.   Wind speeds measured
here were,  as expected,  greater than those  recorded at  the other four stations,
which varied in  exposure  and were not situated as close to the  lake shore.   All
stations showed  markedly  decreased  wind speeds in May,  with the Bruce station
on the  lake  shore  showing the largest  relative decrease.

     Mean current  speeds  at  the three levels of measurement in the upper 50 m
of the  water  column showed only  insignificant differences  during the months of
December 1974 through April  1975, when the  water mass  of  Lake Huron was nearly
homogeneous.   Current  speeds near the bottom were  less,  but followed closely
the trend of  speed increase  or decrease in  the near surface water.   The slack-
ening of current speeds during February and March 1975  was greater than would
be predicted by  simple  relationships with the observed  wind speeds and was
probably caused  by  ice  cover during these months.   Since a majority of the cur-
rent meters were placed within 20 km of the coast,  the mean current speeds are
weighted toward  what  is occurring in the coastal zone.   But this area is where
the ice is.   A  rapid  decrease in current speeds at  all  levels in May,  as the
nearshore waters were  rapidly warming,  was  caused by  lessening wind stress on
the lake surface,  due in part  to the  intense atmospheric  stability over the
lake surface.

     For the  ice-free,  warm weather months  of April through October,  a compara-
tively  large quantity of  current and water  temperature  data has been collected
in the  Great Lakes.   Figure 13  (Bennett  and Baylor, 1974)  shows a  typical  re-
sult  of current  studies during  this  season of the year,  with mean  current  speeds
                                        24

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                                         20'-
                                              LAKE ONTARIO
                                              RMS CURRENT SPEED AT
                                              10,15,30,450 m DEPTH
                                 /\
                                 i  \
 Figure 13.   Lake-wide  average  of
   the MS current speed  at  four
   depths observed in Lake  Ontario
   during 1972 (from Bennett and
   Baylor, 1974) .
C/5 151
O^
a
UJ
UJ
5
   10-
                                             MAY
             JUN
                   JUL   AUG
                      1972
SEP   OCT
increasing  steadily  from  small values in May  and  with considerable vertical
gradients of  horizontal  current velocity from higher  speeds  near the surface
and decreasing with  depth.   RMS values of current speed  are  presented in this
figure and  the  trend of increasing kinetic energy at  all depths throughout the
ice-free season is clear.   The general increase in  energy  in Lake Ontario was
found to be associated with a similar trend in  the  surface wind stress over
the lake, a trend characteristic of the Great Lakes region.   Peak energy levels
in late June, early  August,  and early October were  related to three intense
storms.   Studies  in  the  other Great Lakes have  shown  similar trends  of seasonal
kinetic energy increase.

     Comparisons  of  power  spectra  computed from flow  data  collected  during the
ice-free months indicate  that the  seasonal increase in  kinetic  energy is gen-
eral across all  frequencies  and is  especially  pronounced at near-inertial, fre-
quencies, when the lakes are  strongly density stratified.   While these seasonal
changes correspond with  increasing momentum flux from the  surface wind stress,
the greater growth  at near-inertial  frequencies represents  the  fact that,  with
stratification,  the  dominant  response  of the  lake to  forcing  is  in  the form of
inertia-gravitational  internal  waves.   The internal wave activity causes the
mean current  speeds  to be  greater  than would be observed in  the absence of
stratification and accentuates  the vertical gradient  of  horizontal  velocity.

     It is  apparent  that we  observe  an  annual cycle in  the  lakewide distribu-
tion of kinetic energy.   Starting  from very low current  speeds  in late spring,
which result  from high stability  in  the overtake boundary  layer because of warm
                                       25

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air over a cold lake  surface,  average current  speeds  increase in a  rather
steady  fashion at all  water depths in response  to a similar seasonal trend in
applied wind  stress.  Horizontal  current  speeds decrease rapidly with depth,
with vertical  gradients  in  harmony with  the spreading and  thickening density
discontinuities in a stably Stratified water ma** as summer progresses.   With
very stable stratification,  kinetic energy  grows  rapidly in favored near-iner-
tial frequencies because  of the  dominant  response of the lake to forcing in the
form of  inertio-gravitational internal waves.   With  the  breakup of  stratifica-
tion in  late  fall,  kinetic  energy is evenly distributed in at least  the  upper
50 m of the water column in Lake Huron and  rises  or  falls  in  close  agreement
with the winter-long trend of applied wind stress.   Volume  transports are
large  during  winter  because of  strong wind Stress and the deep penetration and
stability of the mea" current flow  patterns.   Currents  in  very deep  water are
Significant during  winter and  respond to  increases or decreases in wind  stress
in  the same fashion as  nearer surface intensities.   Ice  formation  is  evidenced
by reduced current  speeds,  as a part  of the  water  Surface is sheltered from
the wind.   Kinetic energy falls  catastrophically  during  late  spring with the
formation  of  a stable  boundary layer of warm  air  over  the  cold lake surface.
Subsequent warming  of  the surface water and the *tart  of stable density Strati-
fication  initiates  the gradual lakewide increase  of current speeds  all over
again.

                 3.7 Comparison  of Summer Current Patterns

     Harrington's  (1895)  current chart of Lake  Huron,  which was  compiled from
drift  bottle  releases  and recoveries during  summer,  is  summarized in  Figure
14.   His studies revealed persistent  southward flowing currents along the west
shore Of the lake and  a return northward flow  along the Ontario  coast as far
north as the mouth of Georgia"  Bay.   Drift  bottles released to the  east of
Georgian Bay had a tendency to meander through the mouth of the  bay and disperse
about its perimeter.   This  feature  led Harrington  to  close a counterclockwise
flow cell in latitudes  just  south of the  bay mouth.   Another cell  of cyclonic
flow was tucked into the northwestern corner  of  Lake Huron  to  account for west-
ward drift observed along  the northern coast of the lake,  i.e.,  the shore ex-
tending northwestward  from  the mouth  of Georgian  Bay.

     Sloss and Saylor (1975)  analyzed current meter  recordings made  in Lake
Huron during  the summer of 1966 and deduc(!d a pattern of flow in epilimnion
water  (Fig. 15).  Again  the circulation of  surface water was  found to be of a
cyclonic nature.  Essential differences from  the  Harrington studies consisted
of enlargement  of the cyclonic circulation cell over the deep  northeastern
basin  of  the  lake.   The  northern  limit of this cell was placed  just east of
the shoal water  that  protrudes nearly 30  km southward from the western end of
Hanitoulin  Island.   Another cyclonic pattern was  found to exist  to  the west of
the  shoal, occupying  a"  area about half the size  indicated  by Harrington.
Sloss and Saylor also  reported a rather steady flow of Lake Huron surface water
into Georgian Bay and a subsurface return  flow of  bay water  into the  lake.
This feature probably accounts  for a  large part of  the difference  in  flow pat-
terns reported j_n the  reaches of Lake Huron east of the bay mouth in the two
studies.
                                       26

-------
        Marie
              LAKE HURON
        j
       'Bay City
    MICHIGAN
  SCALE IN KILOMETERS

20 0 20 40 60 80 100
     ! Ste, Marie
              LAKE HURON
       'Bay City

    MICHIGAN


    20 40  60 BO 100
                  PorT
                HuronS
3Sarnia
                                   Figure 14.   Surface water flM patterns
                                     in Lake Huron during  the open watef
                                     navigation season  (after Harrington,
                                     1835).
                                   Figure 15.   Flow patterns of epilim-
                                     nion water in Lake tiuwn during
                                            (after Sloss  and Saylqr.,1975)

-------
     As the  surface water warms  in spring and  early summer, an epiliranion forms
initially  near  shore  and gradually spreads and  thicken* as  summer  progresses.
Typical features  of surface  water temperature distributions  observed during the
warming cycle are  shown  in Figure 16.   Warm water  confined  in  May  to coastal
areas  gradually expands  lakeward  in July to surround  a  colder,  denser pool of
water  centered  over the  deep northeastern basin of Lake Huron.   Similar distri-
butions observed in 1966 have  been reported by Bolsenga  (1976). Temperature
distributions within  the lake basin on a cross  section  of the  lake  from Black
River, Mich,,  to Tobertnory,  Ont., were taken during the same time  intervals as
the  surface  temperature  measurements (Fig.  17). All isotherms  exhibit similar
characteristics,  being depressed  near  the coast* and  shallow near  the center of
the  lake basin.   This  feature is  not unique to  Lake  Huron,  but rather appears
to be  characteristic  of  the  development  of summer  stratification in all of the
Great  Lakes.

     The importance of  the  temperature distributions  to lake  circulation arises
because of observations  that show  that  in the  Great  Lakes, as in  oceans,  persis-
tent horizontal water  density gradient*  are supported by  nearly geostrophic
current flows,  which  represent a balance between  pressure and Coriolis forces.
A cold core  of  dense  water  surrounded  by warmer,  less dense water  is supported
by currents  flowing counterclockwise about the  cell,  characterized by conver-
gence  (sinking)  along the  coasts  and divergence (upwelling) over the core.
Thus,   the  horizontal  temperature  gradients observed during  the  warm weather
season  on  Lake  Huron  and repeatedly observed year  after year  give  supporting
evidence to  a  circulation pattern very  similar  to the  reported current  surveys.

     Now it  is  also apparent that the winter current  patterns  in  Lake Huron are
very similar to those observed in  summer.  The  winter observations reveal a
deeper penetration  of high  current speeds in the  nearly isothermal  water mass
and  larger volume transports,  which can  be  attributed to larger momentum  fluxes
because of increased wind  speed*.  Winter circulation persists  in  a  character-
istic  cyclonic  pattern  unsupported by significant  horizontal  water density
gradients.    The small  gradients observed exhibit  features  similar  to summer
distributions,  with a denser core of water over the  lake's  deep basin surrounded
by colder, less dense water  and ice about the lake coasts.   The obvious conclu-
sion drawn from these observation* is that the  prevailing wind-driven current
patterns support  the  observed thermal structure (the  currents  are  similar with
or without horizontal  temperature gradients).   It is not the thermal  structure
that drives  the current*.
                                4.   CONCLUSIONS

     Winter  in  Lake  Huron is accompanied  by  an almost isothermal water  mass.
In  1974  the  last vestiges of summer stratification were  observed  in November.
Following  a  month of no  discernible temperature  gradient*  (December),  the win-
ter months  of January,  February,  and March  showed faint temperature differen-
tials  consisting of a pool  of  warmer  water (1  to 2C warmer)  centered over the
lake's deep  northeastern  basin  surrounded by colder water  and  ice about the
lake coasts.  April  exhibited a return to near  isothermal  conditions,  followed
in  May by the start  of the  cyclical v rraing trend.

-------
   auK Ste. Marie
               LAKE HURON
       'Bay City

    MICHIGAN
  SCMEINI lOLOMETERS       )Q >    .   -^
20"'o j?'"*o 6o""8o too  portX S_^/Q
                 Huron4^Sarnia
  'Sault Ste, Mane
              LAKE HURON
       'Bay City

    MICHIGAN
  SCALE IN KILOMETERS
20 0 20  40 60  80 100
                                             ault Ste. Marie
                                                        LAKE HURON
                                                  'Bay City
                                              MICHIGAN
                                                      so 100   port>,
                                                            Hufon^OSarnia
                                       Figure 16.  Surface water tempera-
                                          tures  (C) of  Lake  Huron  as ob-
                                          served in 1971  on  three  CCIW
                                         monitor cruises.   Clockwise from
                                          upper  left  the cruise  dates were:
                                          al  17-25 May,  b)  12-28 June, and
                                         a) 19-27 July.   Temperature s truo-
                                          ture of the lake water mass'is
                                          shown  in  Figure  17 along  the cross
                                          section of the lake shown  here
                                         from Black River,  Mich,, to
                                                   f Ont,

-------
WEST SHORE
   50
 JlOO
 CL.
 UJ
 O
  150
(a)
EAST SHORE
    0
                                  50
                                   too
                                   150
                                          WEST SHone
                                              0
EAST SHORE
    0
                                                                          - 100
                                                                            150
                                                                        EAST SHORE
                                                                            0
 Figure  17.   Temperature  isopleths
   (C)ofthe Lake Huron water mass
   on a cross section  of the lake
   from Black  River,  Mieh,} to
   Tobermorifj Ont.}for  the cruise
   intervals of Figure  16.
                                             -100
                                                                           - 150

-------
     Wind  speeds  about  the perimeter of the  lake  during winter were  relatively
high compared with  winds  during summer.   Instability  in the overwater  atmos-
phere caused by  cold  air  moving over a warmer water  surface peaked in  January,
as did observed wind  speeds.   Unstable conditions  endured  from November  through
March.   April was  a month of nearly neutral  atmospheric stability over the lake
and May was a month of  extreme stability.   With  large momentum fluxes  from the
atmosphere to homogeneous  water in winter, mean  current speeds were  nearly the
same throughout at  least  the  upper 50  m of the water  column.   This  distribution
contrasted vividly  with summer observations  showing  strong vertical  gradients
of horizontal current velocity with depth,  the  velocity gradients being  very
closely related  to  vertical water temperature  (or  density)  gradients.  Month-to-
month variations  of mean current  speeds in winter closely paralleled the tnonth-
to-month variations in  mean wind  speeds observed  about the lake's perimeter,
although ice cover  in February and March  appeared  to  reduce the momentum  flux
from air to water  on  a  whole  basin view.    Intense  stability in the  ova-lake
boundary layer in  May was very effective  in  shielding the  lake surface from sig-
nificant wind stress  and  caused a remarkable decrease in the lake's  kinetic
energy.

     Current patterns in  Lake Huron in winter  1974-75 were dominated by  south-
ward flow  along  the entire west coast south of Alpena.   This southward current
was especially intense  during episodes of  strong west and  northwesterly winds.
With westerly winds prevailing throughout  the winter  months,  southerly flow
along the  west coast  persisted from month  to month and was the most  prominent
feature of the resultant  winter current flow.   The  steady  southward  flow  pene-
trated to  at least  the  50 m  level of  coastal  bathymetry and apparently occupied
a wide coastal strip  with rather uniform  characteristics  (at  least 30  km  wide
just east  of the mouth  of Saginaw Bay).   Large  volumes of  water were transported
southward  in this current.   Much less data was  collected in the eastern half of
the lake.   The available  information suggests that a  broad northward  return  flow
characterizes the current  field in this area.   This  return flow appeared  well
established in the  south  end  of the  lake,   but  the  pattern  was uncertain  in the
northern parts because  of  the scarcity of  data.   Perturbations to  this lakewide
pattern occurred during episodes  of strong wind  stress,  but long period  mean
flows showed a definite preference for cyclonic  flow  during the winter season.

     Flow  patterns  during winter  1974-75  were  very similar to those  observed  in
summer.  Long-lived horizontal  gradients  of water  density  established  in  summer
were supportive of  observed large-scale cyclonic flow and  in  fact may  have
established almost  geostrophic equilibrium.   The  winter current studies,   which
established similar current features existing in  a homogeneous lake,  suggest
that the  summer  thermal structure is  supported  in  part by  the wind-driven lake
circulation,  as  it  is certainly not the temperature  field  that is controlling
current patterns.
                                5.   REFERENCES

Ayers, J, C., D. V. Anderson,  D.  C.  Chandler,  and G. H.  Lauff (1956): Currents
     and water  masses  in Lake Huron, Technical  Paper No.  1,  Great Lakes  Re-
     search  Division,  University  of Michigan,  Ann Arbor,  Michigan.
                                       31

-------
Bellalr,  F.  R.  (1965) :    The  modification of warm air moving over cold water.
     In:   Proceedings,  8th Conference  on Great Lakes Research,  Publication No.
     13,  Great Lakes Research  Division,  The University of Michigan, Ann Arbor,
     Michigan,  249-256.

Bennett,  E. B.,  and  J.  H.  Saylor  (1974):   IFYGL water movement  program -  a
     post  field  work review. In: Proceedings,  IFYGL Symposium,  Fifty-fifth
     Annual  Meeting of the  American Geophysical Union, U.S. Department  of
     Commerce, National Oceanic and Atmospheric Administration, Rockville,
     Maryland,  102-127.

Bolsenga, S.  J, (1976):   Lake  Huron surface water  temperature May-November,
     1966.    Water Resow.  Bull.,  12:147-156.

Danek, L. J.,  and  J. H.  Saylor  (1976):   Saginaw Bay water  circulation,  NOAA
     Technical Report  ERL 359-GLERL 6,   U.S. Department of  Commerce,  Boulder,
     Colorado,  51  pp.

Federal  Water  Pollution Control Administration (1967):  Lake Michigan currents.
     U.S.  Department of Interior,  Federal  Water Pollution  Control  Administra-
     tion, Great  Lakes  Region,  Chicago,  Illinois.

Harrington, M.  W.  (1895):   Surface currents of the  Great  Lakes,  as deduced from
     the movements of  bottle papers during the season of 1892,  1893,  and  1894.
     Bulletin B  (revised), U.S.  Weather  Bureau, Washington,  D.C.,  14  pp.

Hough, J. L.  (1958) :    Geology of  the  Great Lakes,   University of Illinois Press,
     Urbana,  Illinois,   313 pp.

Leshkevich,  G. N.  (1976): Great Lakes ice cover,  1974-1975, NOAA  Technical
     Report  ERL  370-GLERL  11, U.S.  Department  of Commerce,  Boulder,  Colorado,
     39 PP.

Lyons, W. A.  (1970):   Numerical  simulation of  Great Lakes  summertime conduction
     inversions.    In:  Proceedings 13th  Conference  on  Great Lakes  Research,
     International Association  for Great Lakes Research,  369-387.

Millar, F.  G.  (1952):   Surface temperatures of  the  Great Lakes.   J.  Fish.  Res.
     Board Canada, 9:329-376.

Palmer,  M. H., and J.  B. Izatt (1972):    Lake  movements with partial  ice  cover.
     Lirnnol. and Oceanogr, * 17:403-409.

Petterssen,  S.,  and  P. A. Calabrese (1959) : On some weather influences due to
     warming of  the  air by the Great Lakes in  winter.   J.  ofMeteorol.f
     16:646-652.

Phillips,  D. W.  (1972):   Modification of  surface air  over  Lake  Ontario in win-
     ter.  Mon.  Weather Rev., 100:662-670.

-------
Phillips,  D. W., and  J, A. W.  McCulloch  (1972):  The  climate  of the  Great
     Lakes  Basin,  Climatological  Studies No. 20,  Atmospheric  Environment
     Service, Toronto, Canada,  40  pp and illustrations.

Richards,  T. L., H. Dragert,  and  D.  R.  Mclntyre (1966):   Influence  of atmos-
     pheric  stability and  over-water fetch  on winds over  the  lower  Great
     Lakes.   Man.  Weather Rev.,  94:448-453.

Richards,  T. L., J. G. Irbe, and  D.  G.  Massey  (1969):  Aerial  surveys  of Great
     Lakes  water temperatures  April  1966 to  March 1968,  Climatological
     Studies No. 14,  Canada  Department of  Transportation,  Meteorology Branch,
     Toronto, Canada,  55 pp.

Rondy, D. R.  (1969):  Great Lakes ice atlas,  Technical Report, Great Lakes
     Research Center,  U.S. Army Engineer District Lake Survey, Detroit,
     Michigan,   8 pp and  illustrations.

Sheng, Y. P., and  J, B.  Izatt  (1972):   Lake movements with partial  ice cover.
     Litmoi. and Qceanogr.3  17:403-409.

Sloss, P.  W., and  J.  H.  Saylor  (1975) :  Measurements  of current flow during
     summer  in  Lake Huron, NOAA Technical Report  ERL  353-GLERL 5, U.S.  De-
     partment of Commerce, Boulder,  Colorado, 39  pp.

Strong, A. E. (1972):   The influence of a Great Lakes  anticyclone  on atmos-
     pheric circulation.  J. Appl.  Meteorol,, 11:598-612.
                                     33

-------
                                  Appendix A

MONTHLY AND  SEASONAL  WATER CURRENT TRANSPORT  AND  WIND RUN ROSES FOR  CONDITIONS
                 OBSERVED  IN LAKE HURON DURING WINTER 1974-75.

-------
                                ^
           LAKE HURON
            NOVEMBER
           ^ __ KILOMETERS^
           T~iO ~20 "~30'"fo "50
                                                    4?
Figure A,la.   Water current transport roses at 15 m depth  in Lake
  Huron and  wind  run roses  at five perimeter meteorological sta-
  tions for November 1374.   Current  roses show  the percentage  of
  current run toward each octant, while uind roses show the per-
  centage of wind run from each octant.
                                35

-------
oSaginaw
           LAKE HURON
            NOVEMBER 197425m
               KtLOMeTERS_	(
           0  10	20  30  "4
-------
oSaginaw
           LAKE HURON
           NOVEMBER 1974 som
           _., KILOMET|RS
           6  i<520 3cf 40 50
Figure A,la.   Current  roses  at 50  m depth  for November  1974.

-------
            LAKE HURON
       NOVEMBER 1974  2 m ABOVE BOTTOM

               KILOMETERS
Figure A. Id.   Current roses  at 2  m above  the bottom for November
                                1974.
                                  38

-------
          LAKE HURON
           D6C6M8ER 1974 15 m
             KILOMETERS
          0 10  20  30~"40~ 50
Figure A.2a.
Current  roses  at IS m depth and  wind  roses for
          December  1974.
                              39

-------
aSagmaw
           LAKE  HURON
          DECEMBER 1974  25 m
             KILOMETERS
         0  1(T"20  30  40  '"0
i Figure  A,2b.   Current roses at  25 m depth for December 1974.
                                 40

-------
                   5 JO 40 10) * OF TOTAL
oSagmaw
           LAKE  HURON

            DECEMBER 1974 SO m


               KILOMETERS
                    i-^"r  i
                    40   SO
 Figure A.  2s.   Current  roses  at 50  m depth for December  1974.
                                 41

-------
 oSagmaw
            LAKEHURON
       DECEMBER iw am ABOVE BOTTOMi
               KILOMETERS |
                 20 30  40  SO
                                         i
Figure A. 2d.   Current wses at 2  n above  the bottom for December
                                1974.

-------
oSaginaw
           LAKE HURON
            JANUARY 1975 tS m
              KILOMETERS
             10  20 3(T "40
          0              SO
 Figure  A.Sa,
Current  roses  at 15  m depth  and  wind roses fov
           January 1975.
                                  43

-------
         LAKEHURON
          JANUARY 1975  25 m
             KILOMETERS
         CTo  20  30  40 ~5
Figure A.  3b.    Current roses at  25 m  depth  for January  1975.

-------
oSaginaw
           LAKEHURON
            JANUARY t97S SO m
              KILOMETERS^
             10  20 ^0  40 "50
                                            v
 Figure A.Ss,   Current roses  at 50  m depth for January  1975.
                                 45

-------
          DISTRIBUTION
            SCALE
 oSaginaw
            LAKE  HURON
        JANUARY 1975 2 m *806 BOTTOM

                KILOMETERS
            6   10  20  30 40  SO
                                            i
Figure  A.  3d.    Current roses at  2 m above the bottom for  January
                                 1975.
                                   46

-------
          LAKE
          FEBRUARY 1
             KILOME'
            10  20 ^
Figure  A>4a,
Current  roses at 15  m depth and  wind roses  for
          February 1975,
                              47

-------
         UAKE HURON J
          FEBRUARY 1975 
             KILOMETERS
          0 ' ICTM" 30""4Q~5
Figure A. 4b.   Current  roses at 25 m depth for  February 1975.
                              48

-------
cSagmaw
           LAKEHURON
            FEBRUARY 197$ 50m
           	KILOMETERS
           0  (0  Vi  30      SO
 Figure  A.  4c.   Current roses at  50 m  depth for February  1975.

-------
             LAKEHURON
        FEBRUARY t97$  2 m ABOVE BOTTOM

                KILOMETERS
Figure A.  4d.    Current roses at  2 m above the  bottom  for February
                                 1975.

-------
..3*.
 sSaginaw
           LAKE  HURON

             MARCH 1975 15m

              KILOMETERS^

          6  TO  55  30 40  50
 Figure A.5a.   Current roses at  15 m depth and wind  poses for
                            March  1975.
                                51

-------
        LAKE  HURON
             " 1ST5 25 m
           KILOMETERS
Figure A. Sb.   Current roses  at 25 m depth for March 1975.
                              52

-------
        LAKE  HURON
          MARCH  19?5 50m
           KILOMETERS
        0  10  20  30  40  SO
Figure A.5e.   Current roses  at  50 m depth  for March 1975.
                              53

-------
          LAKEHURON

       MARCH 197S 2 m ABOVE BOTTOM

              KILOMETERS
          0   10 20
Figure A. $d.   Current  roses  at 2 m above the  bottom for
                              1975.

-------
          LAKEHURON
            APRIL 1975 15 m

            KILOMETERS
Figure  A.Sa,   Current roses at  15 m depth  and wind roses  for
                          April  1975.
                              55

-------
oSaginaw
         DISTRIBUTION
            SCALE
            LAKE  HURON
              APRIL 1975 2S m
               KILOMETERS
           6 10 20" 30  40 "60
   Fiaure  A. 6b.   Current roses at 25 n depth for  April   1375.
                                    56

-------
        LAKE  HURON
          APRIL 197S 50 rn
            KILOMETERS	
        0  IQ^f0 "30~" 4 0~~50
Figure A,6c.   Current roses  at 50   m depth for April  19?5.

-------
           LAKEHURON
        APRIL 19TS 2m ABOVE BOTTOM

              KiLOMETiRS
Figure A,6d.
Current  roses at  2 m above the bottom for  April
               1975.
                                 58

-------
          LAKE  HURON
            MAV 1iTS 15m
             KILOMETERS
Figure  A.?a,
Current  roses at  15 m depth  and wind roses for
             May  1975.
                                59

-------
        LAKE  HURON
           MAY 1975 25 m
          _  KILOMETER^ 	
        0  10^0  " 30  40""5'0
Fiaure A. 75.    Current roses at  25 m  depth  for  May 1975.
                               60

-------
       LAKE  HURON
         MAY 1975 50 m
Figure A.?c.   Current roses at 50 m depth for May 1975.
                           61

-------
No  current data received from  2 m off the bottom  for May  1975.
                                62

-------
oSaginaw
           LAKE HURON
           WINTER 1974-197S  15 m
              KILOMETERS
           0  1  20 JO   <0   ffl
 Figure A.&a,
Current roses at 15 m  depth and wind roses for
         winter 1974-75.

-------
           LAKE  HURON
           WINTER 1974-t9?S  25m
              KILOMETERS
           0  10  20  30  A)  50
Figure A. St.   Current roses  at 25 m depth for winter 1274-75.
                                  64

-------
   fKvvt^vj7^) /v3-;
            K_/
oSaginaw
          LAKE HURON
          WINTER t974-1975 SO m
             KILOMETERS
            10  20 30 40 SO
                                    !
 Figure A.8s.   Current roses at  50 m  depth for winter 1974-75.
                             65

-------
                    jo 40 eo % or TOTAL
oSagmaw
            LAKE  HURON
       WINTER t974-)75 2m ABOVE  BOTTOM
               KILOMETERS _
            0  10  20
Figure A.  8d.   Current wses at  2 m above the  bottom for  winter
                               1974-75.
                                  66

-------
                                  Appendix  B

WATER CURRENT  TRANSPORT  AND WIND RUN  ROSES FOR SELECTED EPISODES  OF  DIRECTION-
         ALLY  STEADY WIND STRESS IN LAKE HURON  DURING WINTER 1974-75.

-------
         DISTRIBUTION     	
           SC*LE   ^^. ^~S
                  5 JO  40 60 "> OF TOTAL
           LAKE HURON

        20 22 NOVEMBER 1974  15m

              KILOMETERS
          0  10  20  30 40  50
Figure B.la.   Current  roses at  15 m depth  and  wind roses for
                       20-22  November 1974.
                                  68

-------
   Sagmaw
              LAKE  HURON
           20 - 22 NOVEMBER 1974 as
                JdLOMETERS
             0  10 20  30  40  50
Figure  3.  Ib.    Current poses at  25 n depth  for 20-22 November 1974.
                                   69

-------
  oSaginaw
                 KILOMETERS

             0  tO  2'O  30 40 50
           20 - 22 NOVEMBER 1974  SO m
Figure B.lc.    Current roses  at 50  m  depth fOT  20-22 November  1974.
                                     70

-------
iSagmaw
           LAKE HURON
    20  22 NOVEMBER 197* 2 m ASOVI BOTTOM
              KILOMETERS
          0  10  20  30  40  50
Figure B.ld,
Current roses at  2 m above  the bottom for20-22
           Hovember 1974.
                                 71

-------
     LAKE HURON
30 NOVEMBER 2 DECEMBER 1974 15 m
         KILOMETERS
     0  1020  30  40  5C
i
 B. 2a.   Current  roses  at 15m depth  and wind rosesfor
            30  "iOvernber-2  December 1974.

-------
                                                     sg&-  ^^.
                                  X
     yt
                                      \
                                       *
        DISTRIBUTION
          SCALE   	
                 S 20 tO 60 % OF TOTAL


oSaginaw


          LAKE HURON


      30 NOVEMBER - 2 DECEMBER 197*  25 m

              KILOMETERS
I
                                  V-
 M
I
 Figure  B.  2b.   Current roses  at 25  n depth for 30  November-2

                         December  1974.
                                73

-------
        0ISTRIBMTIOKON _-.

                  f^Jt'M *# \tOT trOTTOL



           LAKE  HURON

       NOVEMBER

              KILOMETERS

          0  10  20 30~70  50
    30
               - 2 DECEMBER 197*  SO
Figure  B,2c.   Current poses  at 50  m depth  for  30 November-2
                           December  1974.

-------
oSagmaw                           \

           LAKE HURON
    30 NOVEMBER -2 DECEMBER
               KILOMETERS
           0  10  20  30  40  50
         B.2d,   Current roses  at 2 m above the bottom fop 30
                    November-2 December 19 74.
                               75

-------
                  SJO 40 M % OF TOTAL V   ju.
sSaginaw
/
 LAKE HURON
26 - 29 DECEMBER 197*  15 <
     KILOMETERS^
 6  10 ^IfoiO ' 40 50
 Figure  B.3a.
       Current roses  at 15 m depth  and  wind roses for
              26-23  December  1974.

-------
             LAKE  HURON 
             26 - 29 DECEMBER 1974 25 m
                KILOMETERS
Figure B.Sb.    Current roses  at 25 m  depth for 26-29  December  1974.
                                    77

-------
  oSagma*
             LAKE  HURON
           ae-29 DECEMBER 1874  som
                KILOMeTERS
Figure B.Zc,   Current roses at  50 m depth  for 26-29  December  1974.

-------
                   5 20 0 10 % OF TOTAL
< sSagmaw                           \
            LAKE  HURON
     J6- 29 DECEMBER 197*  2 m ABOVE BOTTOM
            	KILOMETERS
            6 10  20 30  40  50
I ?igure B,Sd.   Current roses  at 2  w above  the bottom for 26-29
                           December 1974.
                                  79

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           9  11 JANUARY 1975 15 m
                KILOMETERS
            0  10  20  30  40  50
Figure B.4a.   Current roses  at IS m depth  and  wind roses  for 9-11
                             January  1975.
                                   80

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                       '-X^m       A. ^B
                 K   -v      >,
            LAKE  HURON

           9 11 JANUARY 1975   25 m

                KILOMETERS ^
            0  10  20 30 40 50
Figure  B.  4b.    Current poses  at 25 m  depth for 9-11 January  1975.
                                  81

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            LAKE  HURON
           9-11 JANUARY 1975  $0 m
               KILOMETERS
           0 " 10'"?0 30 40 570
Figure B.4e.   Current  roses at 50 m depth for 9-11  January 1975.
                                  82

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 sSagmaw
     9-11 JANUARY 197S  2 m ABOVE BOTTOM
              ^KILOMETERS
           0  10 "20  30 40 50
. Figure B. 4d.   Current roses  at 2 m  above  the bottom  for9-11
                            January 1975.
                                  83

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   oSagmaw

              LAKE HURON

            11 - 14 JANUARY 1975  15m
                 KILOMETERS
              0  10' 2ff  30 40  50
Figure B,5a.
Current roses  at 15 m  depth  and wind roses for 11-14
               January  1975.
                                    84

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  oSaginaw
             LAKE  HURON
            11 - 14 JANUARY 197S  25 m
              ____ KILOMETERS
                                          1
Figure B.  Si.   Current roses at  25 m  depth for 11-14  January  1975.
                                    85

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                            = COf TIOTL
  oSagmaw                             \
            LAKE HURON
           11- 14 JANUARY 1975  SO m
                KILOMETERS^
            0 10  20  30  40  50
                                                                       
Figure B.Sc.   Current roses at  50 m depth for 11-14 January 1975.
                                   86

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                  5 20 40 64 *k OF TOTAL
^Sagmaw
           LAKE HURON
    11 - 14 JANUARY 1975  2 m ABOVE 9OTTOM
              KILOMETERS
          0  10  20 30 40 SO
Figure B. 5d.   Current roses at  2 m  above  the bottom  for 11-14
                          January  1975.

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            LAKE HURON

           9 - IS FEBRUARY 19FS 15 m

                KILOMETERS
            0  10 20 30 40 SO
Figure  B.6a.   Current roses at  15  m  depth and  wind roses  for 9-15
                            February 1975.
                                 88

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oSagmaw
          8 - IS FEBRUARY 1975  25 m
              KILOMETERS
           0  10 ""26  3b  40  50
Figure  B,6b.   Current
                             at  25 m depth for 9-15  February 1975.
                                 89

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                    II! IIII 40 UJ % * TOTtOtll
  oSaginaw                             \
             LAKE HURON
           9-1$ FEBRUARY 197S 50m
                KILOMETERS
            0  10  20  30 40 50
Figure B,8s.   Current roses  at 50  m depth for 9-15  February  1975.
                                    90

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                  5 20 40 60 % OF TOTAL
oSagmaw

           LAKE  HURON
    - is FEBRUARY 1975  2 m ABOVE BOTTOM

               KILOMETERS
           0"" 10" 20" 30  40" "50
, Figured."da.
current roses  at 2  m above  the bottom for  9-15
          February  1975.

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            LAKE HURON
        26 FEBRUARY - 6 MARCH 1S7S  1$ m
               KILOMETERS
           0 10"" 20" 36 "40" "
Figure B.
  roses at" 15 w depth and wind rages for
Febmar*y~6 March 1975.
                                 92

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. oSaginaw
       28 FEBRUARY- MARCH 1975  25m
               KILOMETERS
            0   10   20  30  4CT19
  Figure B.  7b.
Current roses at  25 m  depth  for26 February-
           Marah  1975.
                                    93

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oSagmaw
           LAKE  HURON
      26 FEBRUARY -6 MARCH 1975 5om
          0  10 20 30 40 50
  Figure B,?a,
Current  poses  at 50 m depth for26 February-6
          March  1975.
                                94

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         DISTRIBUTION
                  "S )9 ~CS 90 ".',0^ TOTOI.
                                    !
Saginaw
           LAKE  HURON
 FEBRUARY 6 MAf*CH 19?S  2 m  ABOVE BOTTOM
              KILOMETERS
          0  lO~To   30 40  50
                                          M
 Figure B.  7d.    Current roses  at 2  m above  the bottom  for 26
                      Februapy-6 March  1975.
                                  95

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                            ?Q^U
                              tXVv^)        i
            LAKE HURON


            1 - 8 APRIL 1975 15 m

               KILOMETERS

            0  10  20  30  40  50
Figure  B,8a.   Current roses  at 15 m depth and  wind roses  for 1-

                            April  1975.
                                  96

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           LAKE HURON
           1-8 APRIL 1975 25m
              KILOMETERS
           0  10  20 30 40  50
Figure B.8b.  Current roses  at 25 m depth for- 2-8 April 1975.
                                 97

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'Sagmaw
          LAKE HURON
          1 - 8 APRIL 19F5 SO i
             KILOMETERS
          0  10  20 30 40 !
7igure B. So.   Current  roses  at 50 m  depth for 1-8  April  1975.
                                98

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          LAKE  HURON

     1 -  APRIL 197S  2 m ABOVE BOTTOM

             KILOMETERS
         0 10  20 30 40 50
Figure B.
Current  roses  at  2 m above the bottom for 1-
           April 1975.

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             LAKE  HURON
              - 13 APRIL 1975  15 m
                KILOMETERS^
             0  10  "20  30 40  50
Figure B. da.
Current  roses  at 15 m depth and  wind roses fOlC 3-13
              April 1975.

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            LAKE HUROS

              U APRIL 1975 25m
            ,  -KIinMRTF.PS ,
           a ~ ib  20  ao  40  50
Figure 5.3&.   Current roses  at 25 m depth  for  3~13 ^prii 1575.
                                101

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 >Sagmaw
            LAKE  HURON
            3-13 APRIL 7$  50 m
               KILOMETERS
           0 10 20  30  40  50
Figure B. 9s.   Current  roses  at 50  m depth  for  3-13 April W?5.
                                  102

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oSagmaw
           LAKE HURON
      I - 13 APRIL 1975 2 m ABOVE BOTTOM
              KILOMETERS
          0  10  20  30  40  50
 Figure B.9d,
Current roses at  2 m above  the bottom for 3-13
           April 1975.
                                 103

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  oSagmaw
             LAKE  HURON-

              S- 7 M*V 1975  15 m
                KILOMETERS
             0  10  ?0 30  40  50
Figure B.lOa.
Current roses at  15 m depth and wind roses for 3-7
              May 1975.
                                  104

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           3-7 MAY 19?5  25
             KILOMETERS
          I  10  20 30 40 50
Figure ff. lOb.   Current poses at  25 m depth  for 3-7  May 1975.
                               105

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                                  LA/
DSagmaw
           LAKE  HURON

           3 7 MAV 1975 50m

              KILOMETERS

          0 10  20 30 40 50
                                           \ 1
                                           V
 Figure B.Wc.   Current  wses  at 50 m depth for S-? May 1975.
                                106

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No  current data received from  2 m off the bottom  for May  1975.
                               107

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                                    TECHNICALREPORT DATA
                             (1'k-asr rratf lnwitcii>.mf o/r the ivrr/-ir hcjore ii
 I,REPORT NO.
 EPA-90514-75-004
              3. RECIPlENT'SACCCSSIOf*NO.
 I.  TITLE AND SUBTI RE
 Winter Currents  in  Lake Huron
 '. AOTHOfltS)
 James  H.Saylor and  Gerald  S.  Miller
              5.  REPORT  DATE
               December 1976  (date  prepared)
                                                              i. PERFORMING ORGANIZATION CODE
                                                             0. PERFORMING ORGANIZATION REPORT NO
               GLERL Contribution  No.  Ill
 . PERFORMING ORGMMIZATION NAME AND ADDRESS
 U.S.  Department  of Commerce
 National Oceanic  and Atmospheric  Administration
 Great Lakes  Environmental Research  Laboratory
 2300 Washtenaw Avenue, Ann  Arbor, Michigan 48104
              10. PROGRAM ELEMiM  NO.

               2BH155 ('Project B-27. IJLRG-T
              11. CONTRACT/GRANT JMU .

               IAG-D5-0631
 12.  SPONSORING AGENCY NAME AND ADDRESS
 U.S. Environmental  Protection Agency
 Region V
 230 South  Dearborn  Street
 Chicago,  Illinois  60604
              13. TYPE OF REPORT AND PERIOD CQVEREC
               Final
              14. SPONSORING ACtNCY CODE
 16, SUPPLEMENTARY NOTES
 Prepared  for U.S. EPA in  support of the  International  Joint Commission - Upper Lakes
 Reference Group,  Working Group B.
 16. ABSTRACT
      Twenty-one  current meter  moorings were deployed  in Lake Huron  during winter 1974-75
 3ie moorings  were set  in  November 1974  and retrieved  approximately  6  months later.  T^16
 stations were configured on a  coarse  grid to measure  the lake-scale  circulation during
 ?inter.  Water temperature  "as also recorded  in nearly  all  of  the 65  current  meters
 leployed.   Results reveal a  strong cyclonic flow  pattern in the  Lake Huron Basin persist1'
 :hroughout the winter.   The  observed  winter circulation "as in essence very similar  to
 rtiat is no" believed to be the summer circulation of epilimnion  water, although  the
 winter currents  penetrated to  deeper  levels in  the water column  and were more  intense.
 Winter cyclonic  flow persisted in a nearly homogeneous  water mass,  while  summer currents
 exhibited an almost  geostrophic balance  with observed water  density distributions.    This
 suggests that the  current  field driven by prevailing  wind stresses  across the  lake's
 rater surface  may be largely  responsible for  establishing the  horizontal gradients of
 rater density  observed  in the  lake during summer.   Analyses of energetic wind stress
 impulses reveal  the prevailing wind  directions that  drive the  dominant circulation?. Tlre
 winter studies permit a description of  the annual cycle of  horizontal  current speed
 /ariation with depth in Lake  Huron,  and in the  other Great Lakes  as  well.   The  effects  of
 the  ice cover are examined and the distribution and movement of  the ice  cover with
 respect to lake  current and temperature  fields  are discussed.
17.
                                 KEY WOHDS AND DOCUMENT ANALYSIS
                  DESCRIPTORS
b.IDENTIFIERS/OPEN ENDED T E R M S C . COSATI I'icld/CfOUp
 Great Lakes,  Lake Huron, water  currents,
 water  circulation,  thermostructure
 International  Joint
 Commission - Upper  Lakes
 Reference  Study
Field  8.  Earth
Sciences  and
oceanography/
Hydrology and
Limnology
10.  DlSTfllaUTlQN STATfcMENT
 Release  Unlimited
                                               19. SECURITY CLASS {TMsReporti
                             21. NO.  OF PAGES
                             119
                                               2O. SECURITY CLASS (Thispagej
                                                                            22. PRICG
EPA Form 2220-1 (8-73)
                            ftU S GOVERNMENT PRINTING OWCEilWT777-067' 1202 ftEOlON NOJ

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