Mesoscale modeling of katabatic winds over Greenland and comparisons with AWS and aircraft data

Simulations of the katabatic wind system over the Greenland ice sheet for t he two months April and May 1997 were performed using the Norwegian Limited Area Model (NORLAM) with a horizontal resolution of 25 km. The model resul ts are intercompared and validated against observational data from automati c weather stations (AWS), global atmospheric analyses and instrumented airc raft observations of individual cases during that period. The NORLAM is abl e to simulate the synoptic developments and daily cycle of the katabatic wi nd system realistically. For most of the cases covered by aircraft observat ions, the model results agree very well with the measured developments and structures of the katabatic wind system in the lowest 400m. Despite NOR-LAM 's general ability of reproducing the four-dimensional structure of the kat abatic wind, problems occur in cases, when the synoptic background is not w ell captured by the analyses used as initial and boundary conditions for th e model runs or where NORLAM fails to correctly predict the synoptic develo pment. The katabatic wind intensity in the stable boundary layer is underes timated by the model in cases when the simulated synoptic forcing is too we ak. An additional problem becomes obvious in cases when the model simulates clouds in contrast to the observations or when the simulated clouds are to o thick compared to the observed cloud cover. In these cases, the excessive cloud amount prevents development of the katabatic wind in the model.