Surface air temperature

The high elevation, large extent and high albedo of the ice sheet are significant factors for local and regional surface air temperatures although latitude and distance inland are also involved. Steffen and Box (2001) provide a useful summary. For both the eastern and western slopes of the ice sheet, surface air temperatures decrease by about 0.8 °C per degree of latitude. As for general elevation effects, from normalizing all AWS station data to 70° N, annual mean surface air temperatures decrease at a rate of0.71 °C per 100 m. The slope gradient shows large seasonality, however. Based on differences between selected stations, the decline ranges from 0.9-1.0 °C per 100 m in November to as low as 0.4 °C per 100 m in June. Regarding free-air lapse rates (as measured by rawinsondes), the ice sheet is characterized by pronounced low-level inversions (see Chapter 5), which are most strongly expressed during the winter season.

Figure 8.2 gives the mean annual cycles of temperature for 16 of the PARCA sites. February is the coldest month at every site, while July is the warmest. The annual mean temperature is only -30 °CatNGRIP (75.1° N, 42.3° W, 2950 m), ranging from -14 °C in July to -46 °Cin February. The only station with a mean July temperature exceeding the freezing point is JAR-1 (+0.2 °C), located on the west slope (69.5° N, 49.7° W, 962 m). At Summit, summer "highs" are near —8 °C and winter minima around —53 °C. However, there is strong daily variability in winter, which is associated with synoptic activity and katabatic winds. Steffen and Box (2001) find that the annual mean temperature range is between 23.5 °C and 30.3 °C for the western slope.

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