Surface climatology of the Greenland Ice Sheet: Greenland Climate Network 1995–1999

The Greenland climate network has currently 18 automatic weather stations (AWS) distributed in most climate regions of the ice sheet. The present network captures well the regional climates and their differences in the accumulation region of the ice sheet. An annual mean latitudinal temperature gradient of −0.78°C/1° latitude was derived from the AWS data for the western slope of the ice sheet, and an annual mean latitudinal temperature gradient of −0.82°C/1° latitude was derived for the eastern slope. The mean annual lapse rate along the surface slope is 0.71°C/100 m, with monthly mean lapse rates varying between 0.4°C/100 m in summer and 1.0°C/100 m in winter. The annual range of monthly mean temperatures is between 23.5°C and 30.3°C for the western slope of the ice sheet, with increasing ranges from south to north and with increase in elevation. The annual mean air temperature was found to be 2°C warmer for the central part of Greenland for the time period 1995–1999, as compared to the standard decade 1951–1960. This annual mean temperature change decreased to approximately 1°C for the elevation 1000–2000 m, whereas at lower elevations, no AWS data are available with sufficient spatial and temporal coverage to verify any temperature trend. Firn temperatures (10-m depth) at high-elevation sites were found to be colder than the mean annual air temperature of the preceding year for the central part and northern Greenland by as much as 2.5°C. In the percolation zone and at the equilibrium line altitude the firn and ice temperatures at 10 m were consistently warmer than the annual mean air temperature because of percolation of meltwater and the isolation effect of the snow cover. The wind speed and direction are affected by the katabatic outflow of the cold air along the slope of the ice sheet, whereas at higher elevations the large-scale synoptic condition is the dominant factor that governs the wind field. The surface height change at high elevations (accumulation minus sublimation) can be approximated with a linear model over an annual cycle using AWS data, whereas in the ablation region and along the equilibrium line altitude the surface height change shows a strong annual cycle.