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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NOTICE
The NOAA Environmental Research Laboratories do not
approve, recommend, or endorse any proprietary product or
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Laboratories, or to this publication furnished by the NOAA
Environmental Research Laboratories, in-any advertising or
sales promotion which would indicate or imply that the NOAA
Environmental Research Laboratories approve, recommend, or
endorse any proprietary product or proprietary material
mentioned herein, or which has as its purpose an intent to
cause directly or indirectly the advertised product to be
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 0°C 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
~80—SO—TOO
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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5 z
S •£"••
s Q T
t02H=
[47]
105 jg
—
@
I — Ifiil —
1974 1975
J_.0«c. Jan. F«b. MM, *pr. May
II I I | i I : I | I I | I I |
108 g
mm
Temperature^^
Direction -""""""^
1 MOORING
103(
110
111
66
113
116
118
1t9
120
121
I 1974 1975
l_
^ ,..N QfM^_ _Jfl.n .€flJb IA*E. Apf, Ma>y
g I | I I | ! I | i I j I I | I I | I I |
[ai]
03
^ ^
a a
^ B
[til
mi
p
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 8°C 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 25°C/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 0,8°C 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 0.2°C 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 1.6°C 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 3°C. 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 2°C offshore water, was observed about 16 km offshore in Lake Michigan
from bathythermograph surveys (FWPCA, 1967). Although bathythermograph surveys
-------
. 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 0°C
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 1,6°C 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
-------
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 6°C
in the northern half of the lake and just over 7°C 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 4°C. 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.
-------
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 2°C, while over the deep northeastern basin ^water temperature
averaged a little less than 4°C. 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 0°C 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
-------
3.3.5 March 1975
The water temperature patterns of February continued into March, as cold,
near 0°C water surrounded slightly warmer water centered over the deep north-
eastern basin. This warmer water had cooled somewhat from February, however,
and averaged about 2°C 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 1°C 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 10°C 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
-------
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 2.8°C 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 0.3°C at mooring
102 and the maximum was 1.8°C 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
-------
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
H»l 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
-------
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
-------
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
-------
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
-------
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 2°C 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 *80¥6 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.
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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.
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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.
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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.
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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
-------
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
-------
'-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
-------
LAKE HURON
9-11 JANUARY 1975 $0 m
KILOMETERS
0 " 10'"?0 30 40 570
Figure B.4e. Current roses at 50 m depth for 9-11 January 1975.
82
-------
sSagmaw
9-11 JANUARY 197S 2 m ABOVE BOTTOM
^KILOMETERS
0 10 "20 30 40 50
. Figure B. 4d. Current roses at 2 m above the bottom for9-11
January 1975.
83
-------
oSagmaw
LAKE HURON
11 - 14 JANUARY 1975 15m
KILOMETERS
0 10' 2ff 30 40 50
Figure B,5a.
Current roses at 15 m depth and wind roses for 11-14
January 1975.
84
-------
oSaginaw
LAKE HURON
11 - 14 JANUARY 197S 25 m
____ KILOMETERS
1
Figure B. Si. Current roses at 25 m depth for 11-14 January 1975.
85
-------
= COf TIOT»L
oSagmaw \
LAKE HURON
11- 14 JANUARY 1975 SO m
KILOMETERS^
0 10 20 30 40 50
±
Figure B.Sc. Current roses at 50 m depth for 11-14 January 1975.
86
-------
5 20 40 64 *k OF TOTAL
^Sagmaw
LAKE HURON
11 - 14 JANUARY 1975 2 m ABOVE 9OTTOM
KILOMETERS
0 10 20 30 40 SO
Figure B. 5d. Current roses at 2 m above the bottom for 11-14
January 1975.
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LAKE HURON
9 - IS FEBRUARY 19FS 15 m
KILOMETERS
0 10 20 30 40 SO
Figure B.6a. Current roses at 15 m depth and wind roses for 9-15
February 1975.
88
-------
oSagmaw
8 - IS FEBRUARY 1975 25 m
KILOMETERS
0 10 ""26 3b 40 50
Figure B,6b. Current
at 25 m depth for 9-15 February 1975.
89
-------
II! IIII 40 UJ % * TOTtOtll
oSaginaw \
LAKE HURON
9-1$ 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
-------
. 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
-------
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
-------
?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
-------
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
-------
'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
-------
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
-------
>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
-------
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
-------
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
-------
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
-------
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
-------
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 OWCEilWT—777-067' 1202 ftEOlON NOJ
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