Heat, momentum and moisture budgets of the katabatic layer over the melting zone of the west Greenland ice sheet in summer

Abstract

The budgets of momentum, heat and moisture of the atmospheric boundary layer over- lying the melting zone of the west Greenland ice sheet during an 8-day period in summer are calculated. To do so, the governing budget equations are derived and presented in terms of ver- tically averaged quantities. Moreover, stationarity is assumed in the present study. Measurements collected during the GIMEX-91 experiment are used to calculate the contribution of the different terms in the equations to the budget. During smnmer, a well developed katabatic wind system is present over the melting zone of the Greenland ice sheet. The budgets show that advection in the katabatic layer is small for momentum, heat and humidity, when the horizontal length scale of the integration area is sufficiently large (>50 km). This indicates that in principle one-dimensional atmospheric models can be used to study the boundary layer over the melting zone of the Greenland ice sheet. The background stratification plays a crucial role in the heat and moisture budget. Vertical divergence of longwave radiation provides one-third and the turbulent flux of sensible heat the rest of the cooling of the boundary layer. Moisture is added to the boundary layer by evaporation which is a significant term in the moisture budget. Negative buoyancy (katabatic forcing) dominates the momentum budget in the downslope direction. Coriolis forcing is important, stressing the large spatial scale of the katabatic winds on the Greenland ice sheet.