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Weather and Solar Radiation Measurements and Mount Takahe

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Weather and solar radiation The weather was recorded one to six times each day, as condi- tions permitted, from 21 December 1984 through 18 January measurements and 1985 primarily around the base of Mount Takahe (112°05W Mount Takahe and Mount Murphy, 76°17S) but also for 5 days near Mount Murphy (111°15W 75°24S). The Mount Murphy data is recorded at the 800-meter West Antarctica site, (camp 7). Table 1 summarizes these recordings which are in- stantaneous values at the time of actual recording with the exception of temperature maximums and minimums. They are M. LOSLEBEN the maximums and minimums for that Greenwich-Mean-Time day. Time is in Coordinated Universal Time (or Greenwich Mountain Research Station Mean Time) which is the local Mount Takahe time minus 17 University of Colorado hours. Temperature was measured with a Taylor max/mm "U" Nederland, Colorado 80466 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 in- During our geological trip to Marie Byrd Land, (party mem- side the box. (2) During snow storms, snow would pack inside bers Nick Banks, Nelia Dunbar, Pam Ellerman, Wes LeMasurier, the box. The number of observations taken per day is shown on Mark Losleben, and Bill McIntosh) took weather observations table 1. Of course, the more times the following parameters are and short-wave solar radiation measurements. These measure- measured the better such values represent the true condition. ments may be some of the first ever taken in the area. 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 Predominant Barometric wind Temperature pressure Wind direction (in degrees Celsius) (in millibars) Elevation Number of range (in grid Predominant Date (in meters) Max. Mm. Ave. observations Max. Mm. (in knots) degrees) visibility Camp 1 12/21/84 1200 -8 -19 13.5 2 823.23 822.89 12 250 Gc 12/22/84 3 -13 -5 4 838.81 825.94 0-1 300 F 12/23/84 4.5 -10 -2.75 840.16 12/24/84 -6 -11 -8.5 6 853.37 847.27 15-22 295 P 12/25/84 -5 -10 -7.5 4 846.60 839.15 2-17 95 P Camp 2 12/26/84 1300 -3 -10 -6.5 3 818.83 811.72 0 G 12/27/84 0 -12 -6 4 817.81 815.78 0-8 90 G 12/28/84 -4.5 -16 -10.2 3 819.51 817.47 0 G 12/29/85 2 -19 -8.5 2 819.51 818.83 0 G 12/30/84 -3 -14 -8.5 4 819.51 818.83 0-21 45 G 12/31/84 -14 -7.5 3 828.65 824.92 16-24 50 G 832.71 831.02 Camp 3 01/01/85 1450 -4.5 -12 -8.8 2 807.65 807.32 0 G 01/02/85 -1 -12 -6.5 3 805.62 802.24 0-9 000 G 01/03/85 -12 -5.5 3 801.90 796.48 0-2 000 G Camp 4 01/04/85 1325 -9 -17 -12.5 3 819.17 816.46 11-20 330 N 01/05/85 -12 -14 -13 4 819.84 818.83 7-10 340 P 01/06/85 -9 -13 -10.5 3 820.86 819.51 9-11 340 G 01/07/85 -7 -13 -10 3 822.55 821.54 0-4 340 G Camp 5 01/08/85 (travel) -8--10 -9 2 832.71 827.97 0-9 20 G 01/09/85 1400 -16 -8.5 4 826.28 825.60 4-12 20 G Camp 6 01/10/85 (travel) 14 -14 2 826.96 823.56 0 G 1200 Camp 7 01/11/85 800 -7 -12 -9.5 2 886.90 886.90 7-12 20 G 01/12/85 -7 -12 -9.5 2 890.28 891.97 2-15 20 G 01/13/85 b8? -12 3 893.67 891.30 0-7 20 G 01/14/85 10? -8 3 894.01 893.67 0 G 01/15/85 8? -8 2 890.62 885.20 0 G Camp 8 01/16/85 1200 6? -10 2 816.80 812.73 5 280 N 01/17/85 4.5 -18 -6.3 2 816.12 815.44 2-3 150 G 01/18/85 2 -20 -9 6 819.17 816.80 0-2 130 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 against the National Oceanic and Atmospheric Administration snow, whereas the west side had no "smooth" area at all. The (Boulder, Colorado) short-wave reference indicates the instru- predominant wind direction as "read" from the snow appears ment is now reading about 1.6 percent low using the pre- to have been from grid north-northwest and then split to "bend" antarctic calibration. Therefore, the true values lie between the around the mountain. reported values and 1.6 percent higher than these reported Solar radiation was recorded from 10 to 17 January 1985 at the values. (See table 2.) Gill Bluff camp (112°44W 76°13S) near Mount Takahe but only Figures 1 and 2 show the total incoming radiation in 20- the entire days of 11 to 16 January are shown in table 2. This is minute totals by day with the total for that day in the lower right total incoming (direct plus diffuse), short-wave (285- to 2,800- corner. The ordinate is energy in kilojoules per square meter nanometer) radiation reaching the ground. Short-wave radia- while the abscissa is time in Greenwich Mean Time hours. By tion is that which clouds block out when they cover the sun. visual observation at the site, days 11 and 12 were fairly clear, This was sensed with an Epply precision spectral pyranometer, and day 16 was overcast. recorded on a Campbell CR-21 logger and powered by a solar To gain a little perspective, some comparisons were made photovoltaic panel. with other sites and with calculations. I did all the calculations according to the Smithsonian Meteorological Tables (Sixth edi- Table 2. Mount Takahe daily radiation totals tion) and assume a transmissivity coefficient of 0.70. This coeffi- cient was chosen because studies conducted by Jacobs (1973) Energy indicated an average transmission coefficient of 0.70 to 0.75. In Kilojoules per According to Jacobs (1978), the arctic station of Resolute Day square meter In Langleysa (74°43N) received an average daily total of 390 Langleys for the month of July, which would correspond to January in the Ant- 11 16,435 (16,698)b 393 (399) arctic. This value is 62.6 percent of the calculated value of direct 12 16,779 (17,047) 401 (407) plus diffuse short wave reaching the ground at Resolute. The 13 14,771 (15,007) 353 (359) Mount Takahe values ranged from a high of 63.2 to 60.7 percent 14 15,296 (15,541) 365 (371) to a low of 51.6 to 50.0 percent of their corresponding calculated 15 14,563 (14,796) 348 (354) values. 16 13,811 (14,032) 330 (335) Thus, for these 6 days in January, this antarctic site compared Average 15,276 (15,520) 365 (371) closely, though a bit lower, to a similar (by latitude) arctic site. Percentage of Some possible mitigating factors could have been the proximity calculated value 60.7 (62.3) 50.0 (51.6) of Mount Takahe and greater cloud coverage. Compared to a high altitude, mid-latitude site (3,749 meters a 1 Langley equals 1 calorie per square centimeter. elevation, 40°N) the average daily total in July 1984 was 552 Numbers in parentheses are the recorded values plus 1.6 percent Langleys.
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