Dependence of slope lapse rate over the Greenland ice sheet on background climate

Near-surface temperature is among the most important external forcings for ice-sheet models studies. It defines where and how much snow and ice is lost from an ice sheet through surface melt. In currently glaciated areas such as Greenland and Antarctica, an increasing number of near-surface temperature measurements are available from automatic weather stations (Steffen and others, 1996; Ahlstrom and others, 2008; van As and others, 2014). Owing to the fact that ice sheets typically have smooth geometries and large horizontal dimensions, the overlying atmospheric conditions are characterized by smooth near-surface temperature fields, which are, to a great extent, modulated by ice-surface elevation. This enables a spatial interpolation between in situ measurements using an intrinsic linear relation between the surface elevation and near-surface temperature, which is commonly termed a slope lapse rate (here and in the following the slope lapse rate is defined to be positive, if the near-surface temperature decreases with elevation) (Ritz and others in 1997; Fausto and others in 2009).