Weather and solar radiation measurements and Mount ...
Weather and solar radiation measurements and Mount Takahe and Mount Murphy, West Antarctica
M. LOSLEBEN Mountain Research Station University of Colorado Nederland, Colorado 80466
During our geological trip to Marie Byrd Land, (party members Nick Banks, Nelia Dunbar, Pam Ellerman, Wes LeMasurier, Mark Losleben, and Bill McIntosh) took weather observations and short-wave solar radiation measurements. These measurements may be some of the first ever taken in the area.
The weather was recorded one to six times each day, as conditions permitted, from 21 December 1984 through 18 January 1985 primarily around the base of Mount Takahe (112°05'W 76°17'S) but also for 5 days near Mount Murphy (111°15'W 75°24'S). The Mount Murphy data is recorded at the 800-meter site, (camp 7). Table 1 summarizes these recordings which are instantaneous values at the time of actual recording with the exception of temperature maximums and minimums. They are the maximums and minimums for that Greenwich-Mean-Time day. Time is in Coordinated Universal Time (or Greenwich Mean Time) which is the local Mount Takahe time minus 17 hours. Temperature was measured with a Taylor max/mm "U" tube thermometer suspended in a 1-cubic-foot cardboard box, which had slits cut to allow air flow, set on the "ground." This shelter worked very well with two exceptions. (1) From 13 to 16 January, when air speed was virtually nil and the sun was bright, some unrepresentative heating probably occurred inside the box. (2) During snow storms, snow would pack inside the box. The number of observations taken per day is shown on table 1. Of course, the more times the following parameters are measured the better such values represent the true condition. Barometric pressure was read from an aneriod barometer sup-
51
41
2
41
3'
F
0 5 10 GMT 15 20 24 5 10 GMT 15 20 24
Figure 1. Global shortwave incoming radiation (20-minute intervals) for days 11, 12, 13, and 14.
1985 REVIEW
193
plied by the Navy weather center, McMurdo Station. Accurate north equals approximately 112°. East equals 90°.) Visibility for comparisons of barometric pressures can only be made among the day is a measure of the predominant condition for that day. those readings at the same camp or location since these are true [Good (C) means visibility of more than 12 kilometers; fair (F) pressures, not corrected to sea level. To help compare inter- means I to 12 kilometers; poor (P) means 100 meters to I camp readings, in a rough way, the approximate elevations iri kilometer; nil (N) means less than 100 meters.] meters are given on table 1 for each camp. Note camps 1, 6, and During the circumnavigation of Mount Takahe, three 8 are the same location. Wind speeds are in knots and are the "smooth" or "calm" zones were noticed on the north, east, and range of average speeds measured that day. Direction is the south sides (grid direction). These areas were separated by well predominate direction of the day and in grid degrees. (Grid formed sastrugi or wind-roughened surfaces. The north "calm" Table 1. Weather observation summary for Mounts Takahe and Murphy
Temperature (in degrees Celsius)
Date
Elevation (in meters) Max. Mm. Ave.
Camp 1 12/21/84 12/22/84 12/23/84 12/24/84 12/25/84
1200
Camp 2 12/26/84 12/27/84 12/28/84 12/29/85 12/30/84 12/31/84
1300
Camp 3 01/01/85 01/02/85 01/03/85
1450
Camp 4 01/04/85 01/05/85 01/06/85 01/07/85 Camp 5 01/08/85 01/09/85 Camp 6 01/10/85
1325
Barometric pressure (in millibars)
Number of observations Max. Mm.
Predominant visibility
12 0-1
250 300
Gc F
15-22 2-17
295 95
P P
-8 3 4.5 -6 -5
-19 13.5 -13 -5 -10 -2.75 -11 -8.5 -10 -7.5
2 4
-3 0 -4.5 2 -3
-10 -6.5 -12 -6 -16 -10.2 -19 -8.5 -14 -8.5 -14 -7.5
3 4 3 2 4 3
818.83 811.72 817.81 815.78 819.51 817.47 819.51 818.83 819.51 818.83 828.65 824.92 832.71 831.02
0 0-8 0 0 0-21 16-24
-4.5 -1
-12 -8.8 -12 -6.5 -12 -5.5
2 3 3
807.65 807.32 805.62 802.24 801.90 796.48
-17 -12.5 -14 -13 -13 -10.5 -13 -10
3 4 3 3
-9 -16 -8.5
-9 -12 -9 -7
6 4
823.23 822.89 838.81 825.94 840.16 853.37 847.27 846.60 839.15
Wind range (in knots)
Predominant wind direction (in grid degrees)
45 50
G G G G G G
0 0-9 0-2
000 000
G G G
819.17 816.46 819.84 818.83 820.86 819.51 822.55 821.54
11-20 7-10 9-11 0-4
330 340 340 340
N P G G
2 4
832.71 827.97 826.28 825.60
0-9 4-12
20 20
G G
2
826.96 823.56
0
90
(travel) 1400
-8--10
(travel) 1200
14
800
-7 -7 b8? 10? 8?
-12 -9.5 -12 -9.5 -12 -8 -8
2 2 3 3 2
886.90 886.90 890.28 891.97 893.67 891.30 894.01 893.67 890.62 885.20
7-12 2-15 0-7 0 0
20 20 20
G G G G G
1200
6? 4.5 2
-10 -18 -6.3 -20 -9
2 2 6
816.80 812.73 816.12 815.44 819.17 816.80
5 2-3 0-2
280 150 130
N G G
Camp 7 01/11/85 01/12/85 01/13/85 01/14/85 01/15/85 Camp 8 01/16/85 01/17/85 01/18/85
-14
G
a Days are Coordinated Universal Time. (In month/day/year format.) b ? denotes that the value is probably artificially high. See text for definitions. d No data.
None. 194
ANTARCTIC JOURNAL
zone was the largest in the area and also had the deepest soft snow, whereas the west side had no "smooth" area at all. The predominant wind direction as "read" from the snow appears to have been from grid north-northwest and then split to "bend" around the mountain. Solar radiation was recorded from 10 to 17 January 1985 at the Gill Bluff camp (112°44'W 76°13'S) near Mount Takahe but only the entire days of 11 to 16 January are shown in table 2. This is total incoming (direct plus diffuse), short-wave (285- to 2,800nanometer) radiation reaching the ground. Short-wave radiation is that which clouds block out when they cover the sun. This was sensed with an Epply precision spectral pyranometer, recorded on a Campbell CR-21 logger and powered by a solar photovoltaic panel. Table 2. Mount Takahe daily radiation totals Energy In Kilojoules per square meter In Langleysa
Day
11 12 13 14 15 16
16,435 (16,698)b 393 (399) 16,779 (17,047) 401 (407) 14,771 (15,007) 353 (359) 15,296 (15,541) 365 (371) 14,563 (14,796) 348 (354) 13,811 (14,032) 330 (335)
Average
15,276 (15,520) 365 (371)
Percentage of calculated value 60.7 (62.3) 50.0 (51.6)
a 1 Langley equals 1 calorie per square centimeter. Numbers in parentheses are the recorded values plus 1.6 percent
The surrounding topography was a flat (less than 1°) ice sheet with this exception: Mount Takahe was to the grid north and described a relatively smooth arc of height 8° above the horizon tapering to the horizon on both sides. The azimuth of the 5° altitude point on each side was 55°. The instrument used has not yet been officially recalibrated since returning from Antarctica; however, an initial check
against the National Oceanic and Atmospheric Administration (Boulder, Colorado) short-wave reference indicates the instrument is now reading about 1.6 percent low using the preantarctic calibration. Therefore, the true values lie between the reported values and 1.6 percent higher than these reported values. (See table 2.) Figures 1 and 2 show the total incoming radiation in 20minute totals by day with the total for that day in the lower right corner. The ordinate is energy in kilojoules per square meter while the abscissa is time in Greenwich Mean Time hours. By visual observation at the site, days 11 and 12 were fairly clear, and day 16 was overcast. To gain a little perspective, some comparisons were made with other sites and with calculations. I did all the calculations according to the Smithsonian Meteorological Tables (Sixth edition) and assume a transmissivity coefficient of 0.70. This coefficient was chosen because studies conducted by Jacobs (1973) indicated an average transmission coefficient of 0.70 to 0.75. According to Jacobs (1978), the arctic station of Resolute (74°43'N) received an average daily total of 390 Langleys for the month of July, which would correspond to January in the Antarctic. This value is 62.6 percent of the calculated value of direct plus diffuse short wave reaching the ground at Resolute. The Mount Takahe values ranged from a high of 63.2 to 60.7 percent to a low of 51.6 to 50.0 percent of their corresponding calculated values. Thus, for these 6 days in January, this antarctic site compared closely, though a bit lower, to a similar (by latitude) arctic site. Some possible mitigating factors could have been the proximity of Mount Takahe and greater cloud coverage. Compared to a high altitude, mid-latitude site (3,749 meters elevation, 40°N) the average daily total in July 1984 was 552 Langleys. Mount Takahe (1,200 meters, 76°S) was 371 Langleys. Even though the sun shines for 24 hours in Antarctica, its rays must penetrate a thicker atmosphere to reach the Earth's surface. The author wishes to thank all the members of the field party, Rudy Haas, the National Oceanic and Atmospheric Administration, and Ruth Cameron for their help in making this article possible. This research was supported in part by National Science Foundation grant DPP 80-20836 to W.E. LeMasurier.
500
500
400
400
KJ/M2
KJ/M2
300
300
200
200
100
tOO
0
0 5 10 15 20 24 5 10 15 20 240 GUT GUT
Figure 2. Global shortwave incoming radiation (20-minute intervals) for days 15 and 16. 1985 REVIEW
195
References
Jacobs, J.D. 1978. Radiation climate of Broughton Island. In R.G. Barry, and J.D. Jacobs, (Eds.). Energy budget studies in relation to fast-ice breakup processes in Davis Strait.
Jacobs, J.D. 1973. Synoptic energy budget studies in the eastern Baffin IslandDavis Strait region. (Unpublished Doctoral Thesis, University of Colorado, Department of Geography.) Smithsonian Meteorological Tables, (Sixth Revised Edition). Prepared by Robert J. List, Fourth Reprint Issued 1968. (Smithsonian Miscellaneous Collections, Volume 114.) Washington, D.C.: Smithsonian Institution Press.
Katabatic wind interaction with Inexpressible Island, Terra Nova Bay D.H. BROMWICH
Z_
$ :6'
Institute of Polar Studies Ohio State University Columbus, Ohio 43210
....,/Harsel1 (%490, \\ , VTeoll N
Ice o -
Each winter, Terra Nova Bay (figure 1) is kept mostly free of ice by strong katabatic winds which continually blow down the Reeves Glacier from the east antarctic plateau and cross the flat Nansen Ice Sheet (Bromwich and Kurtz 1984). High wind speeds and low air temperatures lead to very high ice production rates in this recurring polynya (Kurtz and Bromwich 1985); the ice is continually blown away by the wind keeping the water open. Formulation of these ideas depended upon historical, regional, and satellite data. Quantitative in situ observations are being acquired to test these inferences. The katabatic outflow is monitored by an automatic weather station (Aws) which is located on the southern part of Inexpressible Island. Data for February through April 1984 and February through April 1985 reveal that the katabatic wind nearly always blows from the direction of the Reeves Glacier (from 3000 with a directional constancy of 0.98) at an average speed of 17.1 meters per second. These values are very close to those inferred from 1912 historical records (Bromwich and Kurtz 1982, 1984) and suggest that this site is the second windiest in the Antarctic. Because the AWS (at 78 meters above sea level) is situated within 3 kilometers of terrain which rises to elevations well in excess of 200 meters, it is important to ascertain whether AWS measurements accurately reflect the upwind katabatic flow. This report summarizes what is known about the island's perturbation of the airflow. The U.S. Navy and U.S. Geological Survey have photographed the western side of Inexpressible Island in five summers between 1956 and 1984. All the air photographs show an accumulation zone below the western cliffs which is surrounded on three sides by bare, probably wind-swept ice. The typical configuration is sketched in figure 1; the widest parts of the zone lie to the north of the southern tip of the 200-meter contour. To the west of the highest point on the island, the zone is about 1 kilometer across and its top is estimated to be 30 meters above the Nansen Ice Sheet (Skinner personal communication). Because this large feature has been observed during numerous summers from both ground and air, it is likely to be permanent (Chinn personal communication). 196
-
k 3
Vegetation :a '
Nansei InexpresslbleA
Is. !\ A20
Ale
Cape Washington
Terra
fF
Russell Hells Gate AWS - Snow Cave 119121
Nova
Sheet - Bay a Anemometer Resultant wind direction Ocean High terrain Fast or Boy ice Elevation contours in meters Spot elevation in motors
DovId 6/.
'Ce
A;;:lb
Accumulation zone on 8 January, 1975
75'30 163E - I64E - 165E
Figure 1. Location map adapted from U.S. Geological Survey 1:250,000 reconnaissance series. Elevation contours in 200-meter increments have been added to labelled glaciers and Inexpressible Island, but omitted from "high terrain" and nunataks (N).
D. Skinner of the New Zealand Geological Survey has studied the geology of Inexpressible Island (Skinner 1983) on three separate occasions, most recently during the 1982— 1983 austral summer. He generously supplied the author with all available meteorological observations (Skinner et al. 1983; Skinner personal communciation). These data identify frequent summer conditions which allow the accumulation zone to persist undiminished. On seven of the days between 7 and 18 January 1983, gale force katabatic winds (speeds exceeding 15 meters per second) from the Reeves Glacier interacted with Inexpressible Island; generally light winds prevailed the remainder of the time. Figure 2 summarizes the observed interaction on all these days between the strong winds (sustained speeds of 25 meters per second were frequently estimated) and the topography of the northern two-thirds of the island. The gale force winds rose ANTARCTIC JOURNAL
M. LOSLEBEN Mountain Research Station University of Colorado Nederland, Colorado 80466
During our geological trip to Marie Byrd Land, (party members Nick Banks, Nelia Dunbar, Pam Ellerman, Wes LeMasurier, Mark Losleben, and Bill McIntosh) took weather observations and short-wave solar radiation measurements. These measurements may be some of the first ever taken in the area.
The weather was recorded one to six times each day, as conditions permitted, from 21 December 1984 through 18 January 1985 primarily around the base of Mount Takahe (112°05'W 76°17'S) but also for 5 days near Mount Murphy (111°15'W 75°24'S). The Mount Murphy data is recorded at the 800-meter site, (camp 7). Table 1 summarizes these recordings which are instantaneous values at the time of actual recording with the exception of temperature maximums and minimums. They are the maximums and minimums for that Greenwich-Mean-Time day. Time is in Coordinated Universal Time (or Greenwich Mean Time) which is the local Mount Takahe time minus 17 hours. Temperature was measured with a Taylor max/mm "U" tube thermometer suspended in a 1-cubic-foot cardboard box, which had slits cut to allow air flow, set on the "ground." This shelter worked very well with two exceptions. (1) From 13 to 16 January, when air speed was virtually nil and the sun was bright, some unrepresentative heating probably occurred inside the box. (2) During snow storms, snow would pack inside the box. The number of observations taken per day is shown on table 1. Of course, the more times the following parameters are measured the better such values represent the true condition. Barometric pressure was read from an aneriod barometer sup-
51
41
2
41
3'
F
0 5 10 GMT 15 20 24 5 10 GMT 15 20 24
Figure 1. Global shortwave incoming radiation (20-minute intervals) for days 11, 12, 13, and 14.
1985 REVIEW
193
plied by the Navy weather center, McMurdo Station. Accurate north equals approximately 112°. East equals 90°.) Visibility for comparisons of barometric pressures can only be made among the day is a measure of the predominant condition for that day. those readings at the same camp or location since these are true [Good (C) means visibility of more than 12 kilometers; fair (F) pressures, not corrected to sea level. To help compare inter- means I to 12 kilometers; poor (P) means 100 meters to I camp readings, in a rough way, the approximate elevations iri kilometer; nil (N) means less than 100 meters.] meters are given on table 1 for each camp. Note camps 1, 6, and During the circumnavigation of Mount Takahe, three 8 are the same location. Wind speeds are in knots and are the "smooth" or "calm" zones were noticed on the north, east, and range of average speeds measured that day. Direction is the south sides (grid direction). These areas were separated by well predominate direction of the day and in grid degrees. (Grid formed sastrugi or wind-roughened surfaces. The north "calm" Table 1. Weather observation summary for Mounts Takahe and Murphy
Temperature (in degrees Celsius)
Date
Elevation (in meters) Max. Mm. Ave.
Camp 1 12/21/84 12/22/84 12/23/84 12/24/84 12/25/84
1200
Camp 2 12/26/84 12/27/84 12/28/84 12/29/85 12/30/84 12/31/84
1300
Camp 3 01/01/85 01/02/85 01/03/85
1450
Camp 4 01/04/85 01/05/85 01/06/85 01/07/85 Camp 5 01/08/85 01/09/85 Camp 6 01/10/85
1325
Barometric pressure (in millibars)
Number of observations Max. Mm.
Predominant visibility
12 0-1
250 300
Gc F
15-22 2-17
295 95
P P
-8 3 4.5 -6 -5
-19 13.5 -13 -5 -10 -2.75 -11 -8.5 -10 -7.5
2 4
-3 0 -4.5 2 -3
-10 -6.5 -12 -6 -16 -10.2 -19 -8.5 -14 -8.5 -14 -7.5
3 4 3 2 4 3
818.83 811.72 817.81 815.78 819.51 817.47 819.51 818.83 819.51 818.83 828.65 824.92 832.71 831.02
0 0-8 0 0 0-21 16-24
-4.5 -1
-12 -8.8 -12 -6.5 -12 -5.5
2 3 3
807.65 807.32 805.62 802.24 801.90 796.48
-17 -12.5 -14 -13 -13 -10.5 -13 -10
3 4 3 3
-9 -16 -8.5
-9 -12 -9 -7
6 4
823.23 822.89 838.81 825.94 840.16 853.37 847.27 846.60 839.15
Wind range (in knots)
Predominant wind direction (in grid degrees)
45 50
G G G G G G
0 0-9 0-2
000 000
G G G
819.17 816.46 819.84 818.83 820.86 819.51 822.55 821.54
11-20 7-10 9-11 0-4
330 340 340 340
N P G G
2 4
832.71 827.97 826.28 825.60
0-9 4-12
20 20
G G
2
826.96 823.56
0
90
(travel) 1400
-8--10
(travel) 1200
14
800
-7 -7 b8? 10? 8?
-12 -9.5 -12 -9.5 -12 -8 -8
2 2 3 3 2
886.90 886.90 890.28 891.97 893.67 891.30 894.01 893.67 890.62 885.20
7-12 2-15 0-7 0 0
20 20 20
G G G G G
1200
6? 4.5 2
-10 -18 -6.3 -20 -9
2 2 6
816.80 812.73 816.12 815.44 819.17 816.80
5 2-3 0-2
280 150 130
N G G
Camp 7 01/11/85 01/12/85 01/13/85 01/14/85 01/15/85 Camp 8 01/16/85 01/17/85 01/18/85
-14
G
a Days are Coordinated Universal Time. (In month/day/year format.) b ? denotes that the value is probably artificially high. See text for definitions. d No data.
None. 194
ANTARCTIC JOURNAL
zone was the largest in the area and also had the deepest soft snow, whereas the west side had no "smooth" area at all. The predominant wind direction as "read" from the snow appears to have been from grid north-northwest and then split to "bend" around the mountain. Solar radiation was recorded from 10 to 17 January 1985 at the Gill Bluff camp (112°44'W 76°13'S) near Mount Takahe but only the entire days of 11 to 16 January are shown in table 2. This is total incoming (direct plus diffuse), short-wave (285- to 2,800nanometer) radiation reaching the ground. Short-wave radiation is that which clouds block out when they cover the sun. This was sensed with an Epply precision spectral pyranometer, recorded on a Campbell CR-21 logger and powered by a solar photovoltaic panel. Table 2. Mount Takahe daily radiation totals Energy In Kilojoules per square meter In Langleysa
Day
11 12 13 14 15 16
16,435 (16,698)b 393 (399) 16,779 (17,047) 401 (407) 14,771 (15,007) 353 (359) 15,296 (15,541) 365 (371) 14,563 (14,796) 348 (354) 13,811 (14,032) 330 (335)
Average
15,276 (15,520) 365 (371)
Percentage of calculated value 60.7 (62.3) 50.0 (51.6)
a 1 Langley equals 1 calorie per square centimeter. Numbers in parentheses are the recorded values plus 1.6 percent
The surrounding topography was a flat (less than 1°) ice sheet with this exception: Mount Takahe was to the grid north and described a relatively smooth arc of height 8° above the horizon tapering to the horizon on both sides. The azimuth of the 5° altitude point on each side was 55°. The instrument used has not yet been officially recalibrated since returning from Antarctica; however, an initial check
against the National Oceanic and Atmospheric Administration (Boulder, Colorado) short-wave reference indicates the instrument is now reading about 1.6 percent low using the preantarctic calibration. Therefore, the true values lie between the reported values and 1.6 percent higher than these reported values. (See table 2.) Figures 1 and 2 show the total incoming radiation in 20minute totals by day with the total for that day in the lower right corner. The ordinate is energy in kilojoules per square meter while the abscissa is time in Greenwich Mean Time hours. By visual observation at the site, days 11 and 12 were fairly clear, and day 16 was overcast. To gain a little perspective, some comparisons were made with other sites and with calculations. I did all the calculations according to the Smithsonian Meteorological Tables (Sixth edition) and assume a transmissivity coefficient of 0.70. This coefficient was chosen because studies conducted by Jacobs (1973) indicated an average transmission coefficient of 0.70 to 0.75. According to Jacobs (1978), the arctic station of Resolute (74°43'N) received an average daily total of 390 Langleys for the month of July, which would correspond to January in the Antarctic. This value is 62.6 percent of the calculated value of direct plus diffuse short wave reaching the ground at Resolute. The Mount Takahe values ranged from a high of 63.2 to 60.7 percent to a low of 51.6 to 50.0 percent of their corresponding calculated values. Thus, for these 6 days in January, this antarctic site compared closely, though a bit lower, to a similar (by latitude) arctic site. Some possible mitigating factors could have been the proximity of Mount Takahe and greater cloud coverage. Compared to a high altitude, mid-latitude site (3,749 meters elevation, 40°N) the average daily total in July 1984 was 552 Langleys. Mount Takahe (1,200 meters, 76°S) was 371 Langleys. Even though the sun shines for 24 hours in Antarctica, its rays must penetrate a thicker atmosphere to reach the Earth's surface. The author wishes to thank all the members of the field party, Rudy Haas, the National Oceanic and Atmospheric Administration, and Ruth Cameron for their help in making this article possible. This research was supported in part by National Science Foundation grant DPP 80-20836 to W.E. LeMasurier.
500
500
400
400
KJ/M2
KJ/M2
300
300
200
200
100
tOO
0
0 5 10 15 20 24 5 10 15 20 240 GUT GUT
Figure 2. Global shortwave incoming radiation (20-minute intervals) for days 15 and 16. 1985 REVIEW
195
References
Jacobs, J.D. 1978. Radiation climate of Broughton Island. In R.G. Barry, and J.D. Jacobs, (Eds.). Energy budget studies in relation to fast-ice breakup processes in Davis Strait.
Jacobs, J.D. 1973. Synoptic energy budget studies in the eastern Baffin IslandDavis Strait region. (Unpublished Doctoral Thesis, University of Colorado, Department of Geography.) Smithsonian Meteorological Tables, (Sixth Revised Edition). Prepared by Robert J. List, Fourth Reprint Issued 1968. (Smithsonian Miscellaneous Collections, Volume 114.) Washington, D.C.: Smithsonian Institution Press.
Katabatic wind interaction with Inexpressible Island, Terra Nova Bay D.H. BROMWICH
Z_
$ :6'
Institute of Polar Studies Ohio State University Columbus, Ohio 43210
....,/Harsel1 (%490, \\ , VTeoll N
Ice o -
Each winter, Terra Nova Bay (figure 1) is kept mostly free of ice by strong katabatic winds which continually blow down the Reeves Glacier from the east antarctic plateau and cross the flat Nansen Ice Sheet (Bromwich and Kurtz 1984). High wind speeds and low air temperatures lead to very high ice production rates in this recurring polynya (Kurtz and Bromwich 1985); the ice is continually blown away by the wind keeping the water open. Formulation of these ideas depended upon historical, regional, and satellite data. Quantitative in situ observations are being acquired to test these inferences. The katabatic outflow is monitored by an automatic weather station (Aws) which is located on the southern part of Inexpressible Island. Data for February through April 1984 and February through April 1985 reveal that the katabatic wind nearly always blows from the direction of the Reeves Glacier (from 3000 with a directional constancy of 0.98) at an average speed of 17.1 meters per second. These values are very close to those inferred from 1912 historical records (Bromwich and Kurtz 1982, 1984) and suggest that this site is the second windiest in the Antarctic. Because the AWS (at 78 meters above sea level) is situated within 3 kilometers of terrain which rises to elevations well in excess of 200 meters, it is important to ascertain whether AWS measurements accurately reflect the upwind katabatic flow. This report summarizes what is known about the island's perturbation of the airflow. The U.S. Navy and U.S. Geological Survey have photographed the western side of Inexpressible Island in five summers between 1956 and 1984. All the air photographs show an accumulation zone below the western cliffs which is surrounded on three sides by bare, probably wind-swept ice. The typical configuration is sketched in figure 1; the widest parts of the zone lie to the north of the southern tip of the 200-meter contour. To the west of the highest point on the island, the zone is about 1 kilometer across and its top is estimated to be 30 meters above the Nansen Ice Sheet (Skinner personal communication). Because this large feature has been observed during numerous summers from both ground and air, it is likely to be permanent (Chinn personal communication). 196
-
k 3
Vegetation :a '
Nansei InexpresslbleA
Is. !\ A20
Ale
Cape Washington
Terra
fF
Russell Hells Gate AWS - Snow Cave 119121
Nova
Sheet - Bay a Anemometer Resultant wind direction Ocean High terrain Fast or Boy ice Elevation contours in meters Spot elevation in motors
DovId 6/.
'Ce
A;;:lb
Accumulation zone on 8 January, 1975
75'30 163E - I64E - 165E
Figure 1. Location map adapted from U.S. Geological Survey 1:250,000 reconnaissance series. Elevation contours in 200-meter increments have been added to labelled glaciers and Inexpressible Island, but omitted from "high terrain" and nunataks (N).
D. Skinner of the New Zealand Geological Survey has studied the geology of Inexpressible Island (Skinner 1983) on three separate occasions, most recently during the 1982— 1983 austral summer. He generously supplied the author with all available meteorological observations (Skinner et al. 1983; Skinner personal communciation). These data identify frequent summer conditions which allow the accumulation zone to persist undiminished. On seven of the days between 7 and 18 January 1983, gale force katabatic winds (speeds exceeding 15 meters per second) from the Reeves Glacier interacted with Inexpressible Island; generally light winds prevailed the remainder of the time. Figure 2 summarizes the observed interaction on all these days between the strong winds (sustained speeds of 25 meters per second were frequently estimated) and the topography of the northern two-thirds of the island. The gale force winds rose ANTARCTIC JOURNAL
