Measurements of the katabatic wind in Antarctica

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The authors wish to acknowledge Charles Liddick of the National Earth Satellite Service Office of Operations Support Branch for calculating the satellite reception circles from McMurdo; William Kosco of the U.S. Geological Survey for his support of the project; and Olivia Smith for her preparation of the manuscript. This research was supported by National Science Foundation grants, DPP 79-06412 and DPP 77-27010.

Measurements of the katabatic wind in Antarctica Giw

WENDLER

Geophysical Institute University of Alaska Fairbanks, Alaska 99702

A. Pocci Laboratoire de Glaciologie Universite de Grenoble Grenoble, France

During the austral summer 1979-80, as a part of the U.S.-French joint experiment, three automatic weather stations (Aws) built by Stanford University were installed in 1980 REVIEW

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Figure 5. N0AA-6 AVHRR nearIR visible image (channel 2) of the Amery Ice Shelf.

References Hussey, W. J . 1979. The TIROS-N/NOAA operational satellite system. Washington, D.C.: U.S. Department of Commerce/Noi, National Environmental Satellite Service. Schwalb, A. 1979. The TIROS-N/NOAA A-G satellite series (NoAA Technical Memorandum, NESS 95). Washington, D.C.: U.S. Department of Commerce/No.

Antarctica to investigate the katabatic wind in the French sector. One was placed on Dome Charlie (3,215 meters), the other two at D17 (438 meters) and D10 (267 meters) near Dumont d'Urville Station (66°4('S 140°01'E). Measurements from these stations, together with those obtained by the French scientists, are increasing our data base rapidly, giving hope for a better understanding of this wind phenomenon. This joint French-U.S. experiment will establish additional stations between Dome Charlie and D17, as well as some stations around Dumont d'Urville, during the coming season. Stations at D10 and D17 were installed in January 1980 and at Dome Charlie in February; March 1980 was the first month during which we obtained a full set of data from all three stations. The wind velocities for the three stations are given in figure 1. D10 and D17 have very similar wind conditions, a result to be expected. The winds are steadily downslope, changing their SSE direction very little. Winds are strong, up to 128 kilometers per hour, and are expected 193

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Figure 1. Wind velocities for the three automatic weather stations (Aws) during March 1980. A dot indicates a wind vector coming from the center of the graph. Note the steady, strong downslope winds for D10 (Aws 8901) and D17 (Aws 8900); at Dome Charlie (Aws 8904) the winds are lighter (scale Is different) and more variable.

to increase during winter. In April 1980 winds up to 140 kilometers per hour were measured at 017, and an absolute maximum in wind speed at Dumont d'Urville was recorded at 314 kilometers per hour in midwinter (June)—a speed that will challenge the design of any station. Dome Charlie experiences much lighter winds and the direction is more variable. This is understandable as there is no gravity wind and the wind regime is more like that of the free atmosphere. Temperatures drop to very low values at this highaltitude station. March had a minimum of — 66.1°C, with a mean of — 51.8°C. In April the mean temperature dropped to — 60.3°C, with a minimum of — 73.4°C. An absolute minimum for Antarctica might be measured in the next few months, assuming, of course, that our station stays operational at these low temperatures. The diurnal variation in the wind speed at D10 during March is given in figure 2. 017 showed a very similar course. The maximum is observed during the night, and the minimum at noon. Note that local noon is around 3 a.m. Greenwich mean time. Furthermore, data were used only when Dome Charlie had wind speeds below 8 kilometers per hour, that is, in the absence of strong cyclonic activities. These results are expected for a gravity wind and were previously reported from French observations. In figure 3 the wind speed at D10 is plotted against the temperature difference between D10 and Dome C, the assumption being that the greater the temperature difference, the stronger the gravity wind. Some indication of this effect can be seen, at least for stronger wind speeds. it is also interesting to note

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the very large temperature differences which, most of the time, are far above the adiabatic rate. Since the surface winds are always offshore, this can be explained by relatively warm maritime air, which is moved at a somewhat elevated level inland and is mixed into the surface layer, hence warming the coastal stations. This large temperature difference is, of course, the driving force of a gravity wind. This work is being supported by National Science Foundation grant DPP 77-26379. Allen Peterson's group of Stanford University designed the stations. They were installed by Robert Flint (010 and 017) and Glenn Rosenberger and Cal Teague (Dome Charlie). Programming was carried out by K. Chen (Stanford University) and Coert Olmsted (University of Alaska). Our thanks to all these people. 40 Eli

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Figure 2. Diurnal variation of wind speed for D10 during March 1980. Note that the wind speed has Its minimum at local noon, around 3 a.m. Greenwich mean time, at a time when the temperature Is at the maximum.

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Figure 3. Wind speed at 010 plotted against the temperature difference of D10 and Dome Charlie for 1980. Note that there is some indication that stronger winds are connected with large temperature difference..

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