A Look at the Surface-Based Temperature Inversion on the Antarctic Plateau

Abstract

Data from radiosondes, towers, and a thermistor string are used to characterize the temperature inversion at two stations: the Amundsen-Scott Station at the South Pole, and the somewhat higher and colder Dome C Station at a lower latitude. Ten years of temperature data from a 22-m tower at the South Pole are analyzed. The data include 2- and 22-m temperatures for the entire period and 13-m temperatures for the last 2 yr. Statistics of the individual temperatures and the differences among the three levels are presented for summer (December and January) and winter (April–September). The relationships of temperature and inversion strength in the lowest 22 m with wind speed and downward longwave flux are examined for the winter months. Two preferred regimes, one warming and one cooling, are found in the temperature versus longwave flux data, but the physical causes of these regimes have not been determined. The minimum temperatures and the maximum inversions tend to occur not with calm winds, but with winds of 3–5 m s−1, likely due to the inversion wind. This inversion wind also explains why the near-surface winds at South Pole blow almost exclusively from the northeast quadrant. Temperature data from the surface to 2 m above the surface from South Pole in the winter of 2001 are presented, showing that the steepest temperature gradient in the entire atmosphere is in the lowest 20 cm. The median difference between the temperatures at 2 m and the surface is over 1.0 K in winter; under clear skies this difference increases to about 1.3 K. Monthly mean temperature profiles of the lowest 30 km of the atmosphere over South Pole are presented, based on 10 yr of radiosonde data. These profiles show large variations in lower-stratospheric temperatures, and in the strength and depth of the surface-based inversion. The near-destruction of a strong inversion at South Pole during 7 h on 8 September 1992 is examined using a thermal-conductivity model of the snowpack, driven by the measured downward longwave flux. The downward flux increased when a cloud moved over the station, and it seems that this increase in radiation alone can explain the magnitude and timing of the warming near the surface. Temperature data from the 2003/04 and 2004/05 summers at Dome C Station are presented to show the effects of the diurnal cycle of solar elevation over the Antarctic Plateau. These data include surface temperature and 2- and 30-m air temperatures, as well as radiosonde air temperatures. They show that strong inversions, averaging 10 K between the surface and 30 m, develop quickly at night when the sun is low in the sky, but are destroyed during the middle of the day. The diurnal temperature range at the surface was 13 K, but only 3 K at 30 m.