Radiation climatology of the Greenland ice sheet

The Greenland ice sheet strongly influences regional and perhaps global climate by altering atmospheric and oceanic circulation and temperature. Therefore, it is of importance to understand the mass and energy exchange of the Greenland ice sheet, and its sensitivity to changing environmental conditions. This requires studies of solar and terrestrial radiation processes, the radiative effects of clouds and aerosols, and the interactions between the surface and the atmosphere.; The most comprehensive set of sensors for documenting changes in the Greenland environment is a space-based observing system. Satellites have significant advantages over conventional meteorological observations in polar regions as they provide temporally and spatially continuous data in a place that is very difficult to access. This research work focuses on methods to calculate the surface radiation balance of the Greenland ice sheet using satellite data from the NOAA AVHRR sensor. The primary objective is to compute the surface albedo and temperature over a five year time period to allow for an investigation of the natural spatial and temporal variability of these parameters. In addition, fluxes at the top of the atmosphere are also calculated which allow for an investigation of the effects of cloudiness.; Results from 1989-1993 show that over this time period the surface temperature and albedo exhibit strong seasonal variability but little interannual variability, especially during summer. Except during 1992, there is no significant trend in the surface temperature and albedo. 1992 was unique in that the surface temperatures were significantly lower than the other years and the albedo was higher. This caused a large reduction in the spatial extent of melt during 1992. Reasons for the lower temperatures could be the eruption of Mt. Pinatubo during 1991 or the El Nino event of 1992. Some interannual variability is seen in winter surface temperatures which reflects the variability in storms. Surface temperatures have been found to vary by as much as 20 degrees over time periods of less than a day.; Greater interannual variability exist in the fluxes computed at the top of the atmosphere. This is a direct consequence of the variability in cloudiness. Following the eruption of Mt. Pinatubo, about 13% less solar radiation was absorbed by the Earth - atmosphere the top of the atmosphere system compared with the previous years. The annual loss at the top of the atmosphere is estimated to be {dollar}-{dollar}62 Wm{dollar}sp{lcub}-2{rcub}{dollar}. Comparison with surface measured outgoing longwave radiation with that at the top of the atmosphere indicates that clouds have a strong surface in the thermal infrared and a slight warming affect at the warming affect at the top of the atmosphere.; Finally, it is interesting to examine the state of the ice sheet in response to an increase in air temperature. For only a 1{dollar}spcirc{dollar}C temperature increase, a significant increase in ablation during June-August will occur, but there will also be a proportionally greater increase of ablation in May and September. If the July surface conditions were to occur earlier, say in May at the equilibrium line altitude, the amount of solar radiation would be doubled, from approximately 50 to 100 Wm{dollar}sp{lcub}-2{rcub}{dollar}. This extra solar input at the surface is then used to heat the snow and cause the surface temperature to rise.