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Surface air flow at the South Pole
Cold Regions Scienceand Technology, 15 (1988) 311-317 Elsevier Science Publishers B.V., Amsterdam -- Printed in The Netherlands
311
Short Communication SURFACE AIR FLOW A T THE S O U T H POLE U w e Radok CIRES (University of Colorado) and Meteorology Deparlment, University of Melbourne, Parkville, Victoria (Australia)
INTRODUCTION The completion and occupation of a new station at the South Pole in January 1975 revived interest in the meteorology of that region. Many o f its features had been established by Dalrymple et al. (1966), but a good deal remained to be learnt about the precipitation processes and products that create the small annual accumulation of around 70 k g / m 2, and also about the micrometeorology of the station's environment. The latter is shaped by the size of the station complex (Figs. 1 and 2) which has facilitated the use o f advanced equipment but could distort the surface flow (especially in conditions of high stability and low wind speeds); this in turn would modify the deposition pattern around the station and other environmental features. This note
describes a small exploratory study o f the air flow near the station and of its katabatic control, implied by the comparatively steady winds from 62 ° (average strength 5 m/s, constancy 80%; cf. Schwerdtfeger, 1970). The measurements reported here were made with Sheppard-type anemometers during a 6-day visit to Pole Station in February 1975. Two of four anemometers quickly succumbed to the cold while the remaining two performed well and comparably in temperatures down to minus 40°C. Three sets of measurements were obtained. For the first and principal set, the two anemometers were mounted 1 m above the surface at points A and B in Fig. 2. In order to offset any differences between the two instruments their positions were interchanged frequently. Details are given
Fig. 1. South Pole Station as seen from the outer anemometer location.
0165-232X/88/$03.50
© 1988 Elsevier Science Publishers B.V.
312
7A
/ / / / / / /
Prevailing wind direction
/
as shown on station plan 0~/
/
Sc hawserrd~f°er~eed (blY97 O)
U
./
145"~ /
B
/'/
Station Anemometer
?
loo
200
300 feet I
Fig. 2. South Pole Station and anemometer locations. in Table 1. Several comparisons of the two anemometers operating side by side showed no significant differences between their wind runs. The actual measurements at A and B comprised 22 pairs of runs of different lengths, as set out in Table 1. The second set of measurements consisted of 5 runs with both anemometers at the same location, but mounted 1 m and 25 cm above the snow surface, respectively. The results served for estimates of the surface roughness and friction velocity and also provided a rough idea of the boundary layer stability (Table 2). The final measurements covered winds and surface elevations during a 30 km vehicular run towards grid 80 degrees. According to Bentley ( 1971 ) the local upslope is in that direction, and the surface is overlain by shallow undulations. The pur-
pose was to obtain almost simultaneous wind measurements from the two sides of such an undulation, and to assess from the wind differences the slope contribution to the surface flow strength and direction.
RESULTS Stagnation of surface flow The wind velocities measured sporadically at points A and B in Fig. 2 are shown in Fig. 3, together with the continuous station record of wind speed and direction at the 10 m level. Figure 4 shows the relative velocity excess at point A over point B
313 TABLE 1 Wind measurements at two points upwind of South Pole Station* Data Time Feb 1975 (hrs:min) 5
6 7
8
9
10
14:32-15:55 15:55-17:53 17:49-19:14 10:45-14:19 10:02-13:00 13:03-15:16 15:22-17:39 17:34-20:31 20:33-23:02 22:58-09:16 9:12-10:02 13:50-16:18 16:13-18:37 20:11-00:02 10:17-13:39 13:36-15:47 19:28-22:06 22:07-23:29 23:30-09:16 09:11-10:39 10:35-11:50 11:52-13:09
Mean time (t-)
VA
VB
JV
AV/VA
Vmas~
(ms -~)
(ms -~)
(ms - I )
(%)
(ms -1)
Direction (degrees)
15:15 16:55 18:30 12:30 11:30 14:10 16:30 19:00 21:45
3.3' (3.0') (3.6") (1.55') 1.90" 1.98' 2.43" 3.15" 3.60' 4.95' 5.15' 4.20' 4.70' 4.42" 2.40" 2.20" 0.95" 0.87" 1.45" 2.93" 2.67" 3.37'
(2.95") (2.95") (2.5") (1.85") 1.95' 1.93" 2.23' 3.10' 3.60" 4.90" 5.20" 4.25" 4.65" 4.20 2.50' 2.20 0.86' 0.86' 1.35' 2.35' 2.72' 2.71"
0.35 (0.05) (1.1) -.30 0.05 0.05 0.20 0.05 0
10.6 (1.7) (30) (-19.4) -2.6 2.5 8.2 1.6 0
3.6 3.1 3.3 3.9 2.1 2.1 3.3 3.1 4.1
035 020 020 340 070 080 080 080 090
7.2 5.7 6.2 5.7 3.6 3.1
110 090 090 080 360 005 (090) 090 090-150 130 110 110
9:40 15:00 17:20 22:00 11:50 14:40 20:45 22:50 09:55 11:15 12:30
-.05 -.05 0.05 0.22 -.10 0 0.09 0.01 0.10 0.58 -.05 0.66
-1 -1.2 1.1 5.3 -4.2 0 9.5 1.2 6.9 19.8 -1.9 19.6
1.0 1.8 3.6 4.1 4.1
VA/
Footnotes
Vm~,
(%)
92 (97) (107) (40) 92 96 73 102 87 72 74 76 78 69 71 85 81 81 65 82
*Note: ' = anemometer no. 790; " = anemometer no. 715. aPoint B 50' further out; bPoint A 50' beyond Point B; cPoint A 150' beyond Point B; aUncertain numbers of full mast dial turns, ~,,,~t, 2.3 m s - ~marked weakening during 07:00-10:00; CVelocity decrease through period; rVariable wind; SMast becalmed. ' = anemometer#790, " = anemometer#715
TABLE 2 Results of profile measurements (February 11, 1975 ) Location
A A A B B
V~ ms- t
1.32 1.71 2.26 2.27 2.50
V~ ms- '
.96 1.23 1.84 1.70 2.12
3V ms- i
.36 .48 ,42 ,57 .38
Log profile
Log linear profile
Zo (mm)
/2. (ms -~ )
zo=0.1 m m u, (ms -1 )
L (m)
z o = l mm u, L (ms -1 ) (m)
6.2 7.2 0.58 4.0 0.11
.104 .139 .122 .165 .110
.031 .044 .063 .056 .074
2.97 2.74 12.13 3.77 299.6
.043 0.055 .088 .078 .103
6.71 5.94 -38.62 10.0 -- 12.45
314 Z"
150
_o
11o
I-O ~ UJ
70
__.~3o
a ~ 350 13 Z 310 270 "
10C~
zd n co 5 10 15 20 0
0
0
0
0
0
0
t WIND MEASUREMENTS AT THE lm LEVEL (For details see table 1.]
Fig. 3. Ten metre wind direction (top curve) and wind speed (bottom curve) at South Pole. The open circles and dots are 1 m wind velocities measured at points A and B, in Fig. 1, respectively (for details see Table 1 ).
in the form 100(A-B)/A% as function of the (station record) wind speed and direction.
Surface roughness, friction velocity, and boundary layer stability The results of the two-level measurements are given in Table 2. The surface roughness length and friction velocity were calculated first with the assumption of a linear dependence of wind velocity on logarithmic height. The friction velocity u. and Monin-Obukhov length L were calculated for a loglinear profile shape, with roughness lengths of 0.1 mm and 1 mm - - values covering the range established for South Pole (Dalrymple et al., 1966) as well as for Byrd Station (Budd et al., 1966). The algebra used is given in the appendix.
DiSCUSS~N Blockage of flow by South Pole Station The seventeen strictly comparable measurements at points A and B in Fig. 2 show that the 1 m velocity was on the average 5% higher at point A than at point B. Five out of seventeen runs gave stronger winds at B. Although the positive mean difference is statistically significant, being 3.4 times its standard deviation (1.46 m/s), this is due entirely to the two largest velocity differences, and all that can be deduced with some confidence is a s l ~ t tendency for the prevalent winds to slow down on their approach to the station. As a consequence, one might expect snowbearing winds to raise the snow surface elevation somewhat more in the surroundings of the station than over the open plateau, in addition to creating snowdrifts behind the station structures.
Mesoscale slope effects
Roughness and stability
Figure 5 shows the winds measured during the vehicular traverse, together with the pro£fle of surface elevation changes, as measured with two Thonen altimeters. The relative surface heights have been corrected for the pressure changes recorded at South Pole Station during the traverse.
Three of the five roughness length estimates calculated from the two-level measurements at A a n d B seem unrealisticallylarge. The remaining two were for 1 m wind speeds larger than 2 m/s and have the expected order of magnitude. In the absence of drifting snow or surface changes it may be assumed that the roughness length remained constant be-
315
10m WIND SPEED, m/s 3
20
4 w
5
,•
10
:#
-10 20
10
1 0
-10 340
,
|
0
|
I
2'0
I
40
/
60
I
I
80
I
I
I
100
I
I
120
I
I
140
10m WIND DIRECTION, d e g r e e s ~
Fig. 4. Wind velocity differences between points A and B as functions of wind speed and direction~
tween 0.1 mm and 1 mm throughout this period of relatively light winds. The range of computed values then illustrates merely the low precision obtainable from 2-level measurements. The same applies for the limits to the friction velocity u, and the Monin-Obukhov length L, calculated with assumed roughness lengths of 0.1 mm and 1 mm. These limits are given in the last column of Table 2; they range from stable (positive L) to unstable (negative L) conditions. While the former are more plausible, the possibility of unstable boundary layer stratifications has been confirmed by convection plume signatures in acoustic sounder records that were being obtained at the South Pole by Neff and Hall (1976) at that time, as well as by later micrometeorological studies. Finally, some of the winds recorded by the sta-
tion anemometer (labelled Vmastin Table 1 ) provide a further estimate for the roughness length. The slightly stronger and sustained wind velocities on February 8 were on the average one third larger at the 10 m than at the 1 m level. This gives the roughness length the value Zo= lO-V'/(v'°-V')m= 1 mm as before.
Mesoscale katabatic effects /
The wind measurements during the outward leg of the short traverse (Fig. 5 ) could not be repeated as intended during the return leg, because the driver of the vehicle experienced the onset of frostbite. As far as the outward measurements go (and taking into
316 24 aS measured, ruary 1975
22 20 18 t6
'
g)
////'i:!i
mvv!!olfcemi tmei:ant\\ \\
~xx
Height d i f f e r e n c e
12
E
/
10
/
8 6
/
..............
\-~--corrected for pressure fall \ from 1400 to 1800 hrs.
/
iol2,6 5
1"51ek,\
/
\
4 20-
x
o~ ~ 2.05
1.32Ne
/e2.95 \e j
J
3.3 !
w
f
I
2
4 25
6 48
8 65
I
10 88
1'2 103
14 120
I
lf6 137
1'8 152
20 m i l e s minutes
time after start
Fig. 5. Surface elevation profile and wind velocities along 80 ° E track from South Pole Station. consideration also a small wind change at the station during the run) they show stronger flow along the undulation slope that accentuates the general upslope towards 80 ° E.
CONCLUSION
This exploratory investigation suggests that the current South Pole Station complex has a slight blocking effect on the nearby surface flow. Subsequent boundary layer measurements in the area investigated may therefore have given results that are not fully representative of conditions on the open plateau. The traverse measurements are compatible with the slope effect established by Dalrymple et al. (1966) from comparisons of surface and higherlevel winds and confirm its validity on the local scale.
ACKNOWLEDGEMENTS The anemometers for the wind measurements at the Pole were provided by the CSIRO Division of Atmospheric Physics, and the Thonen altimeters by the Surveying Department of Melbourne University. This help and that of numerous people in Washington, D.C., Christchurch, N.Z., McMurdo, and at the Pole made the work possible and is gratefully acknowledged.
APPENDIX Estimation of roughness length Zo friction velocity u. and Monin-Obukhov length L from pairs of wind velocity measurements (a) For two velocities V~,V2 from a logarithmic profile
317
Solved for L: Ui
Vz=---~ln(z/zo)
V 2-71 - - V 1 z2
1/",/ I"2 = (lnz~ - lnzo) / (lnz2 - lnzo)
.'. Zo = z ; ' / ~ V / z ~"/~
where
AV=V~-V2.
L = f l Vllnz'2
V21nz~
with specific numbers,
With z~=l m and z:= 1/4 m
z~ = 1, z 2 = 1 / 4 ,
k=0.4,
/~=7
this simplifies to u, = 0 . 4 [ Zo = (4 v,/.~v) -l
V , / 4 - V2
1
(3/4)1--i-~zo+ ]-.386]
Also
L= - 7
u,
Vl - V2 =--~ ln(zl/z2) kdV kAV U*-ln( z,/z~_)-ln( 4zl ) with specific numbers, k = 0 . 4 ,
REFERENCES In 4 = 1.386
u, = 0.293 V (b) For realistic Zo, in the range 0.1 m m to 1 m m a log-linear profile o f the f o r m U,
can be used to calculate a slightly different value o f u, and also an estimate of L. In the following, z' = z~ Zo solved for u,:
V, I1",_ u, (!nz', lnz~) -71
Z2 ~T
\
Z1
u,=k z2V,-z, z2 lnZ'l - z l lnz
V2 - VI/4 A Vlnzo + 1.386 Vt
Z2
Bentley, C.R., (1971). Secular increases of gravity at South Pole Station. In: A.P. Crary (Ed.), Antarctic Snow and Ice Studies II. Antarctic Res. Ser. 16, Amer. Geophys. Union, pp. 191-198. Budd,W.F., Dingle, W. and Radok, U., (1966). The Byrd Drift Project: Outline and basic results. In: M.J. Rubin (Ed.), Studies in Antarctic Meteorology. Antarctic Res. Set. 9, Amer. Geophys. Union, pp. 71-134. Dalrymple, P.C., Lettau, H.H. and Wollaston, S., (1966). South Pole Meteorology Program: Data analysis. In: M.J. Rubin (Ed.), Studies in Antarctic Meteorology. Antarctic Res. Ser. 9, Amer. Geophys. Union, pp. 13-58. Neff, W.D. and Hall, F.F., Jr., (1976). Acoustic sounder measurements of the South Pole boundary layer. Preprint volume of the 17th Conf. Radar Meteorology, Seattle (October 26-29, 1976), Amer. Meteorol. Soc., pp. 297302. Schwerdtfeger, W., (1970). The Climate of the Antarctic. In: S. Orvig ( Ed. ), Climates of the Polar Regions. World Survey of Climatology 14, Pergamon, pp. 253-355.
311
Short Communication SURFACE AIR FLOW A T THE S O U T H POLE U w e Radok CIRES (University of Colorado) and Meteorology Deparlment, University of Melbourne, Parkville, Victoria (Australia)
INTRODUCTION The completion and occupation of a new station at the South Pole in January 1975 revived interest in the meteorology of that region. Many o f its features had been established by Dalrymple et al. (1966), but a good deal remained to be learnt about the precipitation processes and products that create the small annual accumulation of around 70 k g / m 2, and also about the micrometeorology of the station's environment. The latter is shaped by the size of the station complex (Figs. 1 and 2) which has facilitated the use o f advanced equipment but could distort the surface flow (especially in conditions of high stability and low wind speeds); this in turn would modify the deposition pattern around the station and other environmental features. This note
describes a small exploratory study o f the air flow near the station and of its katabatic control, implied by the comparatively steady winds from 62 ° (average strength 5 m/s, constancy 80%; cf. Schwerdtfeger, 1970). The measurements reported here were made with Sheppard-type anemometers during a 6-day visit to Pole Station in February 1975. Two of four anemometers quickly succumbed to the cold while the remaining two performed well and comparably in temperatures down to minus 40°C. Three sets of measurements were obtained. For the first and principal set, the two anemometers were mounted 1 m above the surface at points A and B in Fig. 2. In order to offset any differences between the two instruments their positions were interchanged frequently. Details are given
Fig. 1. South Pole Station as seen from the outer anemometer location.
0165-232X/88/$03.50
© 1988 Elsevier Science Publishers B.V.
312
7A
/ / / / / / /
Prevailing wind direction
/
as shown on station plan 0~/
/
Sc hawserrd~f°er~eed (blY97 O)
U
./
145"~ /
B
/'/
Station Anemometer
?
loo
200
300 feet I
Fig. 2. South Pole Station and anemometer locations. in Table 1. Several comparisons of the two anemometers operating side by side showed no significant differences between their wind runs. The actual measurements at A and B comprised 22 pairs of runs of different lengths, as set out in Table 1. The second set of measurements consisted of 5 runs with both anemometers at the same location, but mounted 1 m and 25 cm above the snow surface, respectively. The results served for estimates of the surface roughness and friction velocity and also provided a rough idea of the boundary layer stability (Table 2). The final measurements covered winds and surface elevations during a 30 km vehicular run towards grid 80 degrees. According to Bentley ( 1971 ) the local upslope is in that direction, and the surface is overlain by shallow undulations. The pur-
pose was to obtain almost simultaneous wind measurements from the two sides of such an undulation, and to assess from the wind differences the slope contribution to the surface flow strength and direction.
RESULTS Stagnation of surface flow The wind velocities measured sporadically at points A and B in Fig. 2 are shown in Fig. 3, together with the continuous station record of wind speed and direction at the 10 m level. Figure 4 shows the relative velocity excess at point A over point B
313 TABLE 1 Wind measurements at two points upwind of South Pole Station* Data Time Feb 1975 (hrs:min) 5
6 7
8
9
10
14:32-15:55 15:55-17:53 17:49-19:14 10:45-14:19 10:02-13:00 13:03-15:16 15:22-17:39 17:34-20:31 20:33-23:02 22:58-09:16 9:12-10:02 13:50-16:18 16:13-18:37 20:11-00:02 10:17-13:39 13:36-15:47 19:28-22:06 22:07-23:29 23:30-09:16 09:11-10:39 10:35-11:50 11:52-13:09
Mean time (t-)
VA
VB
JV
AV/VA
Vmas~
(ms -~)
(ms -~)
(ms - I )
(%)
(ms -1)
Direction (degrees)
15:15 16:55 18:30 12:30 11:30 14:10 16:30 19:00 21:45
3.3' (3.0') (3.6") (1.55') 1.90" 1.98' 2.43" 3.15" 3.60' 4.95' 5.15' 4.20' 4.70' 4.42" 2.40" 2.20" 0.95" 0.87" 1.45" 2.93" 2.67" 3.37'
(2.95") (2.95") (2.5") (1.85") 1.95' 1.93" 2.23' 3.10' 3.60" 4.90" 5.20" 4.25" 4.65" 4.20 2.50' 2.20 0.86' 0.86' 1.35' 2.35' 2.72' 2.71"
0.35 (0.05) (1.1) -.30 0.05 0.05 0.20 0.05 0
10.6 (1.7) (30) (-19.4) -2.6 2.5 8.2 1.6 0
3.6 3.1 3.3 3.9 2.1 2.1 3.3 3.1 4.1
035 020 020 340 070 080 080 080 090
7.2 5.7 6.2 5.7 3.6 3.1
110 090 090 080 360 005 (090) 090 090-150 130 110 110
9:40 15:00 17:20 22:00 11:50 14:40 20:45 22:50 09:55 11:15 12:30
-.05 -.05 0.05 0.22 -.10 0 0.09 0.01 0.10 0.58 -.05 0.66
-1 -1.2 1.1 5.3 -4.2 0 9.5 1.2 6.9 19.8 -1.9 19.6
1.0 1.8 3.6 4.1 4.1
VA/
Footnotes
Vm~,
(%)
92 (97) (107) (40) 92 96 73 102 87 72 74 76 78 69 71 85 81 81 65 82
*Note: ' = anemometer no. 790; " = anemometer no. 715. aPoint B 50' further out; bPoint A 50' beyond Point B; cPoint A 150' beyond Point B; aUncertain numbers of full mast dial turns, ~,,,~t, 2.3 m s - ~marked weakening during 07:00-10:00; CVelocity decrease through period; rVariable wind; SMast becalmed. ' = anemometer#790, " = anemometer#715
TABLE 2 Results of profile measurements (February 11, 1975 ) Location
A A A B B
V~ ms- t
1.32 1.71 2.26 2.27 2.50
V~ ms- '
.96 1.23 1.84 1.70 2.12
3V ms- i
.36 .48 ,42 ,57 .38
Log profile
Log linear profile
Zo (mm)
/2. (ms -~ )
zo=0.1 m m u, (ms -1 )
L (m)
z o = l mm u, L (ms -1 ) (m)
6.2 7.2 0.58 4.0 0.11
.104 .139 .122 .165 .110
.031 .044 .063 .056 .074
2.97 2.74 12.13 3.77 299.6
.043 0.055 .088 .078 .103
6.71 5.94 -38.62 10.0 -- 12.45
314 Z"
150
_o
11o
I-O ~ UJ
70
__.~3o
a ~ 350 13 Z 310 270 "
10C~
zd n co 5 10 15 20 0
0
0
0
0
0
0
t WIND MEASUREMENTS AT THE lm LEVEL (For details see table 1.]
Fig. 3. Ten metre wind direction (top curve) and wind speed (bottom curve) at South Pole. The open circles and dots are 1 m wind velocities measured at points A and B, in Fig. 1, respectively (for details see Table 1 ).
in the form 100(A-B)/A% as function of the (station record) wind speed and direction.
Surface roughness, friction velocity, and boundary layer stability The results of the two-level measurements are given in Table 2. The surface roughness length and friction velocity were calculated first with the assumption of a linear dependence of wind velocity on logarithmic height. The friction velocity u. and Monin-Obukhov length L were calculated for a loglinear profile shape, with roughness lengths of 0.1 mm and 1 mm - - values covering the range established for South Pole (Dalrymple et al., 1966) as well as for Byrd Station (Budd et al., 1966). The algebra used is given in the appendix.
DiSCUSS~N Blockage of flow by South Pole Station The seventeen strictly comparable measurements at points A and B in Fig. 2 show that the 1 m velocity was on the average 5% higher at point A than at point B. Five out of seventeen runs gave stronger winds at B. Although the positive mean difference is statistically significant, being 3.4 times its standard deviation (1.46 m/s), this is due entirely to the two largest velocity differences, and all that can be deduced with some confidence is a s l ~ t tendency for the prevalent winds to slow down on their approach to the station. As a consequence, one might expect snowbearing winds to raise the snow surface elevation somewhat more in the surroundings of the station than over the open plateau, in addition to creating snowdrifts behind the station structures.
Mesoscale slope effects
Roughness and stability
Figure 5 shows the winds measured during the vehicular traverse, together with the pro£fle of surface elevation changes, as measured with two Thonen altimeters. The relative surface heights have been corrected for the pressure changes recorded at South Pole Station during the traverse.
Three of the five roughness length estimates calculated from the two-level measurements at A a n d B seem unrealisticallylarge. The remaining two were for 1 m wind speeds larger than 2 m/s and have the expected order of magnitude. In the absence of drifting snow or surface changes it may be assumed that the roughness length remained constant be-
315
10m WIND SPEED, m/s 3
20
4 w
5
,•
10
:#
-10 20
10
1 0
-10 340
,
|
0
|
I
2'0
I
40
/
60
I
I
80
I
I
I
100
I
I
120
I
I
140
10m WIND DIRECTION, d e g r e e s ~
Fig. 4. Wind velocity differences between points A and B as functions of wind speed and direction~
tween 0.1 mm and 1 mm throughout this period of relatively light winds. The range of computed values then illustrates merely the low precision obtainable from 2-level measurements. The same applies for the limits to the friction velocity u, and the Monin-Obukhov length L, calculated with assumed roughness lengths of 0.1 mm and 1 mm. These limits are given in the last column of Table 2; they range from stable (positive L) to unstable (negative L) conditions. While the former are more plausible, the possibility of unstable boundary layer stratifications has been confirmed by convection plume signatures in acoustic sounder records that were being obtained at the South Pole by Neff and Hall (1976) at that time, as well as by later micrometeorological studies. Finally, some of the winds recorded by the sta-
tion anemometer (labelled Vmastin Table 1 ) provide a further estimate for the roughness length. The slightly stronger and sustained wind velocities on February 8 were on the average one third larger at the 10 m than at the 1 m level. This gives the roughness length the value Zo= lO-V'/(v'°-V')m= 1 mm as before.
Mesoscale katabatic effects /
The wind measurements during the outward leg of the short traverse (Fig. 5 ) could not be repeated as intended during the return leg, because the driver of the vehicle experienced the onset of frostbite. As far as the outward measurements go (and taking into
316 24 aS measured, ruary 1975
22 20 18 t6
'
g)
////'i:!i
mvv!!olfcemi tmei:ant\\ \\
~xx
Height d i f f e r e n c e
12
E
/
10
/
8 6
/
..............
\-~--corrected for pressure fall \ from 1400 to 1800 hrs.
/
iol2,6 5
1"51ek,\
/
\
4 20-
x
o~ ~ 2.05
1.32Ne
/e2.95 \e j
J
3.3 !
w
f
I
2
4 25
6 48
8 65
I
10 88
1'2 103
14 120
I
lf6 137
1'8 152
20 m i l e s minutes
time after start
Fig. 5. Surface elevation profile and wind velocities along 80 ° E track from South Pole Station. consideration also a small wind change at the station during the run) they show stronger flow along the undulation slope that accentuates the general upslope towards 80 ° E.
CONCLUSION
This exploratory investigation suggests that the current South Pole Station complex has a slight blocking effect on the nearby surface flow. Subsequent boundary layer measurements in the area investigated may therefore have given results that are not fully representative of conditions on the open plateau. The traverse measurements are compatible with the slope effect established by Dalrymple et al. (1966) from comparisons of surface and higherlevel winds and confirm its validity on the local scale.
ACKNOWLEDGEMENTS The anemometers for the wind measurements at the Pole were provided by the CSIRO Division of Atmospheric Physics, and the Thonen altimeters by the Surveying Department of Melbourne University. This help and that of numerous people in Washington, D.C., Christchurch, N.Z., McMurdo, and at the Pole made the work possible and is gratefully acknowledged.
APPENDIX Estimation of roughness length Zo friction velocity u. and Monin-Obukhov length L from pairs of wind velocity measurements (a) For two velocities V~,V2 from a logarithmic profile
317
Solved for L: Ui
Vz=---~ln(z/zo)
V 2-71 - - V 1 z2
1/",/ I"2 = (lnz~ - lnzo) / (lnz2 - lnzo)
.'. Zo = z ; ' / ~ V / z ~"/~
where
AV=V~-V2.
L = f l Vllnz'2
V21nz~
with specific numbers,
With z~=l m and z:= 1/4 m
z~ = 1, z 2 = 1 / 4 ,
k=0.4,
/~=7
this simplifies to u, = 0 . 4 [ Zo = (4 v,/.~v) -l
V , / 4 - V2
1
(3/4)1--i-~zo+ ]-.386]
Also
L= - 7
u,
Vl - V2 =--~ ln(zl/z2) kdV kAV U*-ln( z,/z~_)-ln( 4zl ) with specific numbers, k = 0 . 4 ,
REFERENCES In 4 = 1.386
u, = 0.293 V (b) For realistic Zo, in the range 0.1 m m to 1 m m a log-linear profile o f the f o r m U,
can be used to calculate a slightly different value o f u, and also an estimate of L. In the following, z' = z~ Zo solved for u,:
V, I1",_ u, (!nz', lnz~) -71
Z2 ~T
\
Z1
u,=k z2V,-z, z2 lnZ'l - z l lnz
V2 - VI/4 A Vlnzo + 1.386 Vt
Z2
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