-------
20
March 24, 1971
On March 24, 1971, the southeastern United States was
dominated by a large mass of polar continental air centered over
southern Minnesota. The upper wind flow was north-easterly on
the surface backing to west-north-west up to 18,000 feet. The air
was relatively dry and stable up to 18,000 feet and winds were fairly
strong; upper winds at 18,000 feet were 80 knots. The high temp-
erature during this period was 52 and the low 30. The area of pre-
cipitation barely skirts the Atlanta area and quite possibly some
shower activity was experienced.
These data also provided what is considered an expected growth
and decay pattern in turbulent mixing. The clearing sky in the morn-
ing hours contributed this pattern by allowing unrestricted solar
heating.
There are several interesting observations for this date.
Shortly after the noon hour the sky became clear thus allowing unob-
structed radiant energy transfer. Surface temperatures continued to
rise, peaking about 1700 hours, the mixing height somewhat followed the
surface temperature pattern but the turbulence indicator displayed a
decaying pattern from the 1400 hours. There is no readily apparent
reason for this latter behavior.
-------
21
FIGURE 8.
ATMOSPHERIC BEHAVIOR
ATLANTA, GEORGIA
MARCH 24, 1971
0700 0800 0900 1000 IIOQ 1200 1300 1400 1500 1600 1700 1800 I9OO 2000
TIME - EST
-------
22
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24
March 18, 1971
On March 18, 1971, a high pressure ridge extending from
Pittsburg, Pennsylvania, to Columbia, South Carolina covered most
of the eastern half of the nation. The lower level circulation
over Gainesv'lle was from the east. The winds at 18,000 feet were
west-north-west at 30 to 40 knots. This was a polar continental
air mass but with moisture coming in at lower levels due to the
easterly winds. The temperature regime during the 24-hour period
reached a high of approximately 76 and a low of 38. There was no
precipitation for this 24-hour period.
This was a clear day with unusually large excursion in surface
temperature. This resulted in high values of turbulence indicator
with a very dramatic collapse in this indicator and turbulence mix-
ing height near sunset.
Surface temperature and mixing height roughly peak at the
same hour; some three hours after the turbulence indicator peak.
-------
25
70
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FIGURE 10.
ATMOSPHERIC BEHAVIOR
GAINESVILLE, FLORIDA
MARCH 18, 1971
10 M
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28
November 17, 1970
On November 17, 1970, a weak high pressure area covered
the eastern half of the nation. The pressure gradient was weak
and Gainesville surface circulation, which was westerly, was
dominated by a high pressure center in the Gulf about 100 miles
south of Pensacola. Winds aloft were generally westerly and at
18,000 feet were about 300 , at 20 knots. This was a polar con-
tinental air mass with relatively dry air. The Gainesville area
experienced a high temperature in the neighborhood of 63 with lows
in the high twenties. There was no precipitation during the 24-
hour period.
This was a clear day with a large excursion in surface temp-
erature. While values of turbulence indicator did not achieve levels
of some other days, they were reasonably high and dissipated in the
late afternoon exhibiting the dramatic collapse along with mixing
height normally found in this time period. Surface winds were notably
light but westerly.
Surface temperature and mixing height peak at the same hour;
approximately three hours after the turbulence indicator peak.
-------
29
90
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FIGURE 12.
ATMOSPHERIC BEHAVIOR
GAINESVILLE, FLORIDA
NOVEMBER 17, 1970
j
00 0700 0800 0900 1000 1100 1200 1300 1400 1500 1600 1700 1800 1900
TIME - EST
-------
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32
May 31, 1971
On May 31, 1971, a weak high pressure area dominated the
southeastern part of the country. The canter of the high was
in northwestern Alabama. The wind flow at lower levels over
Gainesville was north-westerly but very light. At approximately
L8,000 feet, winds were north-westerly at 30 knots. The air was
dry and stable. The temperature regime in Gainesville ranged from
a high of 88 to a low 55 with no precipitation being experienced
during the 24-hour period.
Surface temperature and mixing height follow typical pattern
peaking at approximately 1700 hours. Turbulence indicator pattern
is atypical in that growth stopped as early as 1000-1100 hours, and
did not attain magnitudes that might be expected for a clear day.
Explanation might be associated with light winds and higher than
usual mixing heights attained, thus spreading the energy available
to the higher altitudes.
-------
33
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36
January 20, 1971
On January 20, 1971, Che eastern half of the nation was
dominated by a strong high pressure system centered over north-
western Alabama. Surface winds over Gainesville were north-westerly
at 5 to 10 knots. However, winds in the upper atmosphere were rather
strong; at 18,000 feet winds of over 80 knots were reported. The
temperature during this 24-hour period ranged from -a high of 45 to
a low of 21. There was no precipitation during the period.
This was a clear day and the coldest experienced in the test
program. Turbulence indicator values rose to high levels, drama-
tically decreasing with the approach of sunset. Turbulent mixing
height followed an expected clear day pattern. Generally this would
be considered a typical clear day.
Surface temperature and "mixing height patterns correspond,
each peaking at about 1700 hours. Turbulence indicator attained a
high magnitude and peaked approximately two hours earlier at. 1500
hours.
-------
37
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FIGURE 16.
ATMOSPHERIC BEHAVIOR
GAINESVILLE, FLORIDA
JANUARY 20, 1971
1 1 1 1 1 1 1 1 1 1
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060007000800 0900 1000 1100 1200 1300 1400 1500 1600 1700 1800 1900
TIME - EST
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40
January 21, 1971
On January 21, 1971, the southeastern United States was
under the domination of a continuing high pressure system cantered
over north central Florida. The winds at Gainesville were near
calm in the morning due to the weakness of the pressure gradient
near the center of the high. As the high drifted eastward off the
coast of Florida during the afternoon, winds shifted to southwest
bringing in some low level warm moist air. This moisture layer was
very shallow and no precipitation occurred. The winds at 18,000
feet were backed around from northwesterly on the previous date to
west-north-west on the 21st. They averaged about 30 knots. The
temperature regime during the 24-hour period ranged from a high of
63 to a low of 20.
With clear skies all day, this date experienced an unusually
high temperature excursion from sunup until the high for the day;
some 43 fahrenheit degrees. Winds were light and variable in direc-
tion. The turbulence indicator rose to the highest values experienced
in these series of experiments. The turbulent mixing height pattern
was typical for clear weather.
Surface temperature and mixing height both peaked at approxi-
mately 1600 hours. Turbulence indicator attained quite high magnitudes.
The combination of high turbulence indicator, reasonably high mixing
height and a quite high surface temperature excursion, would seem to
suggest an influence of the warm moist air. The afternoon entry of
this air would suggest super adiabatic lapse rates. Dew point daia
-------
41
recorded by the Gainesville FAA station show the entry of this
moist air. Sufficient data are not available to confirm the super-
diabatic condition.
-------
90 r-
FIGURE 18.
ATMOSPHERIC BEHAVIOR
GAINESVILLE, FLORIDA
JANUARY 21 1971
SOO 0700 0800 0900 1000 1100 1200 1300 1400 1500 1600 1700 1800 1900
TIME - EST
-------
43
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------- An error occurred while trying to OCR this image.
-------
45
May 7. 1971
On the 6th of May, the Bermuda high was centered about
300 miles east of Melbourne, Florida. The pressure gradient
indicated that winds would be south-westerly during the day.
On the 7th, the same pressure system dominated the area. How-
ever, the high had drifted further out to sea and the pressure
gradient weakened considerably. Some low level moisture was
coming in. The winds were very light and variable at times at
the surface. Winds aloft (18,000 feet) were west-south-west
at 20 knots. Dew points on the morning of the 7th were in the
fifties. Surface temperatures cooled to very near the dew point
during the night so that on the morning of the 7th, there was
patchy ground fog all over north Florida. This, however, dissi-
pated quickly after sunrise due to the dryness of the air aloft.
The temperature regime for this date ranged from a high of
89 to a low of 59. There was no precipitation reported in the
Florida area.
This was a day with partial but continuous sky opacity.
The turbulence indicator pattern has an unexplained dip at the time
period that its maximum value might have been expected. Turbulent
mixing height displayed a typical pattern with possibly a slower
collapse rate than observed on some clear days.
Surface temperature and mixing height followed similar pat-
terns, both peaking about 1600 hours. Turbulence indicator also
peaked at this approximate time. The several peaks are not as well
defined as those occurring on some of the days with no cloud cover.
-------
46
90 r-
FIGURE 20.
ATMOSPHERIC BEHAVIOR
GAINESVILLE, FLORIDA
MAY 7, 1971
3800 0900 1000 1100 1200 1300 1400 1500 1600 1700 1800 1900 2000 2100
TIME - EOT
-------
47
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49
May 5, 1971
On May 5, 1971 an eastwardly drifting high pressure center
was located about 300 miles east of Daytona Beach. The Gainesville
area had near calm in the morning but by afternoon winds became
light south-easterly. Some low level moisture existed due to the
winds off the adjacent sea. The winds at 18,000 feet were about
320 at 20 knots. This was a dry and stable air mass. The tempera-
ture regime during the 24-hour period ranged from a high of approxi-
mately 83 to a low of 47. There was no precipitation reported dur-
ing this period.
This was a day with continuous but partial sky opacity. Sur-
face winds were light and variable. Other parameters exhibit what
might be considered expected behavior with respect to buildup and
collapse of the mixing layer.
Surface temperature and mixing height followed similar pat-
terns, both peaking at about 1600 hours. Turbulence indicator also
peaked at this approximate time. The several peaks are not as well
defined as those occurring on some of the days with no cloud cover.
-------
50
90-
80 -
FIGURE 22.
ATMOSPHERIC BEHAVIOR
GAINESVILLE, FLORIDA
MAY 5, 1971
QC.
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TIME - EOT
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53
May 24, 1971
On May 24, 1971, there was a high pressure centered 300
miles east of Wilmington, North Carolina. The high pressure ex-
tended all the way up Hudson Bay. There was an intense low pres-
sure system over the western great lakes with a trough extending
to southern Texas. This deepening low pressure system and trough
in combination with the high produced a strong pressure gradient.
Surface winds for the day were generally southeast to southerly.
The winds at 18,000 feet were about 340 , at 15'knots. The temp-
erature in Gainesville ranged from approximately a high of 88 to
a low of 60. There was no precipitation report for Gainesville
during the 24-hour period.
An interesting day in that the sky opacity increased during
the morning thereafter decreasing in the afternoon, becoming clear
again before sunset. Some anomaly occurred at approximately 1500
hr. as reflected in a sharp decrease in turbulence indicator and
turbulent mixing height. No data available seem to explain this
behavior. The possibility exists that a local rainshower occurred
and did not get recorded on the weather observation sheet. The
rapid collapse prior to sunset is still evident, having occurred some
time after the above anomaly.
-------
90 h
80 -
FIGURE 24.
ATMOSPHERIC BEHAVIOR
GAINESVILLE, FLORIDA
MAY 24, 1971
08000900 1000 1100 1200 1300 1400 1500 1600 1700 1800 1900 2000 2IOO
TIME- EOT
-------
55
1
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c.oi x u - lev aannnv
------- An error occurred while trying to OCR this image.
-------
57
June 22, 1971
The Florida weather of June 22, 1971 was dominated by
a high pressure center located over the central section of the
peninsula. Temperatures ranged from a high of 93 to a low of 73.
Winds in the Gainesville area at about 18,000 feet were west to
west-north-west at 20 knots.
This was a typical summer day in Florida with cumulus
buildups leading to local thunderstorms in the early afternoon.
All data reflect the cooling effect of shower activity. It is
interesting to note the recovery of turbulence indicator and tur-
bulent mixing height with clearing skies in the later afternoon
hours and the collapse of this recovery at a time expected due to
approaching sunset.
-------
58
90 -
FIGURE 26.
ATMOSPHERIC BEHAVIOR
GAINESVILLE, FLORIDA
JUNE 22, 1971
08000900 1000 1100 1200 1300 1400 1500 1600 1700 1800 1900 2000 2100
TIME - EOT
-------
59
------- An error occurred while trying to OCR this image.
-------
61
April 21, 1971
On April 21, 1971, a weak high pressure system centered
approximately 400 miles southeast of the southern tip of the
Florida peninsula dominated the Gainesville weather. Surface
winds were light due to the weak pressure gradient and generally,
southwesterly. Dew points were in the sixties and some ground
fog occurred during the morning hours which quickly burned off.
The maximum temperature attained was 85 and the low 59. The low
level winds bringing moisture off the Gulf produced considerable
cloudiness during the day. Winds at 15,000 feet were about 300 ,
at 25 knots. No precipitation occurred at Gainesville during
the 24-hour period.
The above cloudiness appeared at Gainesville just prior to
noon. This increase in cloud cover stunted the continued increase
in turbulence indicator and turbulence mixing height. In spite of
the cloud cover however these two parameters experienced the rapid
collapse in the hours preceding sunset.
-------
62
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FIGURE 28.
ATMOSPHERIC BEHAVIOR
GAINESVILLE, FLORIDA
APRIL 21, 1971
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June 4, 1971
On June 4, 1971, the southeastern United States was dominated
by a large but weak high pressure system. The high had two centers,
one over eastern Kentucky and the other over eastern South Carolina.
This put the Gainesville area on the southern part of the high and
surface winds during the day were easterly. Considerable low level
moisture caused some patchy ground fog in the early morning which
soon dissipated due to the dryness of the upper air. Winds aloft
were very light and variable. At approximately 18',000 feet, winds
were easterly at 5 knots or less. No precipitation occurred at Gaines-
ville during the preceding 24-hours and the temperature ranged from a
high of approximately 90 to a low of 68.
Considerable cloud cover was experienced all day. The turbu-
lence indicator data reflect a brief effect of & local rainshower. The
rate of collapse of turbulence indicator and turbulent mixing height
is less than experienced on a clear day.
-------
67
90 r
80 -
FIGURE 30.
ATMOSPHERIC BEHAVIOR
GAINESVILLE, FLORIDA
JUNE 4, 1971
0800 0900 1000 MOO 1200 1300 1400 1500 1600 1700 1800 1900 2000 2100
TIME - EOT
-------
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June 15, 1971
June 15, 1971 was a typical summer meteorological situa-
tion. The Bermuda high extended into the Gulf of Mexico with
high pressure centered about 300 miles south of New Orleans.
The surface circulation was generally south to southwest bring-
ing in considerable moisture. The winds at about 18,000 feet
over Gainesville were northwesterly during the day, at 10 knots
or less. The temperature regime ranged from a high of 93 to a
low of 73.
A truly cloudy day with considerable rain and thunder-
storm activity. These activities led to the reduction of tur-
bulence indicator and turbulent mixing height at an early hour.
Surface temperatures dramatically reflect the thundershower cool-
ing effect. It should be appreciated that turbulence surely existed
in and near these thundershowers. Aircraft operations were continued
"in between" such formations.
------- An error occurred while trying to OCR this image.
-------
72
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75
CHANGE IN LAPSE RATES DURING COLLAPSE PERIOD
Lapse rates for the days and hours involved in the study
are summarized in Table I. These rates were determined within
the mixing layer, usually from 200' to 2200' above the surface.
During the late hours the mixing layer is ill-defined due to the
very rapid collapse being experienced; in which case the above
system of determining this rate was used; i.e. no attempt was
made to restrict the lapse rate determination to a height within
the mixing layer. While there are large deviations, it would
seem that the lapse rate becomes more stable with the approach
of sunset.
-------
76
TABLE I
Mixing Height Lapse Rates
with Approach of Sunset
Date
01/21/71
09/13/71
03/18/71
09/14/71
03/24/71
04/21/71
11/17/70
05/05/71
05/07/71
Time
1605
1810
1315
1530
1730
1820
1855
1340
1535
1655
1750
1840
1440
1630
1740
1825
1410
1530
1855
1420
1530
1650
1830
1855
1110
1620
1750
10L9
1405
1550
1815
1945
1010
Time of
Sunset
1757
1949
1838
1949
1843
1900
1745
1909
1910
Lapse Rate
QC/IOO M
0.917
0.753
0.973
0.918
0.868
0.835
0.835
0.902
0.933
0.737
0.836
0.737
0.983
0.885
0.885
0.738
0.885
1.00
1.05
0.852
0.836
0.786
0.770
0.606
1.00
0.852
0.902
0.787
0.860
0.590
0.830
0.787
0.750
-------
77
TABLE I
Continued
1320 0.967
1500 1.007
1630 1.065
1830 1.190
1850 0.950
1920 0.885
1955 0.935
05/24/71 1035 1921 0.983
1310 0.983
1545 1.000
1730 1.037
1840 0.871
1915 1.037
1925 0.837
05/31/71 1350 1923 0.904
1650 0.960
1810 0.950
1930 0.917
06/04/71 1245 1925 0.721
1530 0.902
1640 0.787
1750 0.982
06/15/71 1010 1931 0.819
1110 0.950
1300 1.068
1630 0.640
06/22/71 1000 1932 0.492
1210 0.982
1425 0.862
1600 0.656
1730 0.852
1815 0.819
-------
78
MAPPING OF MIXING HEIGHT OVER URBAN AREAS
Attempts were made to map the mixing height over Atlanta on
3/24/71; over Jacksonville, Florida on 12/11/71 and Tampa, Florida
on 12/12/71. The first two showed very little in the way of a heat
island. The data of 12/12/71 at Tampa, however, did reveal such an
effect, with an increase in the upper limit of turbulence on the
order of 400-500 feet. These data were taken approximately 3-4
hours before sunset at which time the turbulent mixing should have
been at its maximum. Weather was clear with widely scattered clouds
over the downtown area. This procedure was found to be very
difficult from an operational point of view. For any future work
in this area a different approach would be suggested, such as exam-
ining the turbulence indicator amplitude at some uniform altitude
while quickly traversing the urban area in downwind and cross-wind
directions.
-------
79
DIURNAL VARIATION OF TURBULENCE INDICATOR WITH HEIGHT
As explained in Figure 3, in the reduction of data the
turbulence indicator was evaluated at 200 foot intervals for
each sounding and an integrated value for the sounding used for
diurnal plotting purposes. Absent from this system is any in-
dication of the behavior of turbulence as evidenced by this "tur-
bulence indicator" as a function of height above the earth's sur-
face. These data are too numerous to present here in their en-
tirety. Generally this turbulence indicator, and therefore tur-
bulence, was greatest at or near the surface with a progressive
reduction up to the limit of turbulent mixing. Also the magni-
tude of this indicator increased with time throughout the active
mixing layer, maintaining the reduction in magnitude with height,
until that time of day when the inverse process or decay began.
During the decay period, the general period pattern was that the
magnitude of turbulence decreased at all levels, with the near sur-
face levels maintaining the largest although decreasing magnitudes
until virtually all the energy had dissipated and no significant
turbulence was measurable. These phenomena are illustrated in
Figures 34 through 41. The apparent discontinuities or departures
from a linearly reducing magnitude with height are attributed to
the cell structure of atmospheric mixing combined with the fact that
the aircraft was moving through the mobile system rather than sound-
ing in a strictly vertical path.
-------
80
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FIGURE 34.
DIURNAL VARIATION OF TURBULENCE
WITH HEIGHT
24 MARCH 1971
ATLANTA, GEORGIA
SUNSET 1845
I
J
0 2 4 6 8 10 12 14 16
TURBULENCE INDICATOR - Scale Divisions
-------
81
FIGURE 35.
DIURNAL VARIATION OF TURBULENCE
AT GIVEN ALTITUDE
24 MARCH 1971
ATLANTA, GEORGIA
15 r
s
5 10
LJ
O
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ID
CD
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SUNSET I84S
0700 0900 1100 1300
TIME
1500
1700
I9OO
-------
82
FIGURE 36.
DIURNAL VARIATION OF TURBULENCE
WITH HEIGHT
17 NOVEMBER 1970
GAINESVILLE, FLORIDA
5r
SUNSET 1750
0 2 4 6 8 10 12 14 16
TURBULENCE INDICATOR - Scale Divisions
-------
83
FIGURE 37.
DIURNAL VARIATION OF TURBULENCE
AT GIVEN ALTITUDE
17 NOVEMBER 1970
GAINESVILLE, FLORIDA
-------
84
FIGURE 38.
DIURNAL VARIATION OF TURBULENCE
WITH HEIGHT
21 APRIL 1971
GAINESVILLE, FLORIDA
5r
C
O
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O
UJ 2
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J650
SUNSET 1900
I
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0 2 4 6 8 10 12 14 16 18
TURBULENCE INDICATOR-Scale Divisions
-------
85
FIGURE 39.
DIURNAL VARIATION OF TURBULENCE
AT GIVEN ALTITUDE
21 APRIL 1971
GAINESVILLE, FLORIDA
15
cc
O
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9 10
UJ
o
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or
0700
SUNSET 1900
0900
1100
1300
TIME
1500
1700
1900
-------
86
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FIGURE 40.
DIURNAL VARIATION OF TURBULENCE
WITH HEIGHT
18 MARCH 1971
GAINESVILLE, FLORIDA
1340
SUNSET 1838
0246 8 10 12 14 16
TURBULENCE INDICATOR - Scale Divisions
-------
87
FIGURE 41.
DIURNAL VARIATION OF TURBULENCE
AT GIVEN ALTITUDE
18 MARCH 1971
GAINESVILLE, FLORIDA
15
o
g 10
UJ
o
z
UJ
00
cc
13
SUNSET 1838
\2000 AGL
I
0700 0900 1100 1300 1500 1700 1900
TIME
-------
88
CORRELATION OF MEASURED AND PREDICTED MIXING HEIGHTS
Using those days for which an early morning temperature
sounding existed, a correlation was established between the
measured turbulent mixing height and that predicted by the Holz-
worth technique, similar to the study of reference 1 . Antici-
pating poor results during the late afternoon period of turbulent
energy decay, the study was partitioned into an examination of
data taken prior to the beginning of the decay and that taken af-
ter this point in time for a particular day. Figure 42 illustrates
these data prior to the decay, which are comparable to those of re-
ference 1, Figure 4. These data herewith presented have a correla-
tion coefficient of 0.68 versus 0.87 of those in reference 1. The
reduced level of correlation could be due to the inclusion of cloudy
days in the current investigation. Similar data for the measurements
taken during the decay period are shown in Figure 43. As expected,
there is considerably more scatter and the correlation is not as good.
It is interesting to note that although the data are scattered, the
line of best fit, forced through the origin, is very close to the ideal,
indicating a random scatter.
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92
DIURNAL MAXIMA OF TURBULENCE. TEMPERATURE AND MIXING
In an effort to better understand the interrelationships
of surface temperature, turbulent mixing height and turbulence in-
dicator, Table II was prepared which lists the hour at which each
of these parameters reached its peak on the test days.
Surface temperature peaked at an earlier hour than turbu-
lent mixing height on six out of twelve days, the inverse happen-
ing on three days, the inverse happening on three out of twelve.
The above six days were distributed among various- degrees of cloud
cover. The data suggests a delayed reaction of mixing height to
surface temperature but is not conclusive.
Turbulence indicator peaked at an earlier hour than surface
temperature on nine out of twelve days, the inverse happening on
two occasions each of which had significant cloud cover.
Turbulence indicator peaked at an earlier hour than turbulent
mixing height on twelve out of twelve days. Generally the time sep-
arations were significant.
These combinations suggest that the time progression of peak-
ing events is turbulence indicator, surface temperature and finally
turbulent mixing height. The time differential between the latter two
is less distinct. Radiant energy data on several of these experimental
days were available. Review of these data indicates that both all wave-
length and short wave radiant energy peaked at' approximately the same
-------
93
hour as turbulence indicator. Considering that the majority of
this turbulence is considered to be a redistribution of radiant
energy, this correspondence would seem reasonable. It is diffi-
cult to reason the delay in surface air temperature increase. The
delay in peaking of turbulent mixing height can be explained on
the basis of time required for the heated air cells to complete
their rise and resulting establishment of the upper limit of mix-
ing height.
-------
94
TABLE II
TIMES OF MAXIMUM PARAMETER
DATE
09/13/71
09/14/71
03/24/71
03/18/71
11/17/70
05/31/71
01/20/71
01/21/71
05/07/71
05/05/71
05/24/71
06/22/71
04/21/71
06/04/71
06/15/71
TEMPERATURE
1600
1700
1700
1600
1600
1700
1700
1600
15-1600
16-1700
1500
NB
1400
1200
ND
MIXING
HEIGHT
1800
1700
1600
1700
1600
1600
1630
1600
1600
1700
ND
ND
16-1700
1500
ND
TURBULENCE
INDICATOR
1700
1500
14-1500
1330
1330
1400
1500
1500
14-1600
1600
ND
ND
1100
1300
ND
INDICATION
CLOUD
C_OVER
.5
0
0-.2
0
0
0
0
0
.2
.2
.4
.6-. 7 Rain & Thundershowers
.6
.7-.&
.8-1.0 Thunderstorms
ND - Not Well Defined
-------
95
CONCLUSIONS
Atmospheric turbulence as measured by the turbulence in-
dicator described herein undergoes an orderly buildup during the
morning and early afternoon hours and experiences a rapid decay
throughout its active height in the hours preceding sunset.
Turbulent mixing height as measured with an aircraft yaw
accelerometer system also experiences an orderly buildup to a maximum
and with the approach of sunset undergoes a rapid collapse and might be
better described as rapidly losing its identity insofar as defining
an upper limit.
The total turbulent energy within the mixing height attains
a maximum level at a time prior to the attainment of a maximum in
turbulent mixing height or surface temperature.
During the period of decay or collapse in turbulence and tur-
bulent mixing height, there is a trend in the lapse rate toward a more
stable condition, however not in proportion to the total decay or col-
lapse in mixing.
^U.S. Government Printing Office: 1973--7't6-769/ltlf>3 Region No. 'l
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