Simulation of the katabatic flow near the Greenland ice margin using a high-resolution nonhydrostatic model

Abstract

Simulations of the katabatic wind system in the stable boundary layer near the margin of the Greenland ice sheet are presented using the high-resolution (2.8 km) non-hydrostatic Lokal-Modell (LM) of the Deutscher Wetterdienst (DWD). The LM is nested into numerical forecasts provided by the hydrostatic Norwegian Limited Area Model (NORLAM). The area of Kangerlussuaq in West Greenland was selected as the LM domain, since comprehensive measurements of the katabatic wind structure are available for that area (aircraft and AWS). One focus of the LM simulations is to study processes in the transition region between the ice sheet and the tundra, which are not captured by previous model studies because of the micro-scale complexity of the topography. The first simulation is performed for an idealized case using a wintertime atmosphere at rest as initial conditions. For this situation lacking synoptic forcing, a well-developed katabatic wind system is simulated over the inland ice, while a system of fjord winds is simulated in the tundra area. In the second simulation study a realistic case of strong katabatic winds (exceeding 20 m s -1 ) is investigated, and AWS data and vertical profiles from aircraft measurements are used for the model validation. For this real case, the simulation results are in good agreement with instrumented aircraft and automatic weather station observations. While NORLAM fails to reproduce the wind field in the tundra region, the LM simulations show again a pattern of fjord winds and a complex wind field near the ice margin, which agrees with the observed atmospheric state. Because the intensity and the three-dimensional structure of the katabatic winds depend on the specific synoptic environment, the success of the LM simulations is also dependent on the quality of the initial and boundary conditions, i.e. the forecasts of synoptic and mesoscale processes by NORLAM.