Observation andmodelling of gap flow and wake formation on Svalbard

Aircraft observations, satellite information and model simulations are presented for an episode with significant local disturbances in the vicinity of Spitsbergen, on the Svalbard archipelago in the Barents Sea. Relative weak upstream winds from the east gave rise to strong local winds in the Hinlopen Strait which separates Spitsbergen from Nordaustlandet Island. The aircraft data included wind lidar, water vapour lidar and dropsonde observations. The aircraft flew through the Hinlopen Strait and found winds near 20 m s−1 in magnitude close to the surface. This is a factor of about four above the upstream wind magnitude. In the lee of the terrain, a wake with return currents was formed and this was clearly documented by the lidar observations. The model simulations reproduced the episodes with a high degree of fidelity. In the lee of the mountains, small-scale cloud features appeared both in the lidar data and in the satellite observations. For wind directions with easterly and northerly components, these features are frequently observed on satellite pictures downstream of Spitsbergen. In the model framework, the cloud streamers were further investigated. Through sensitivity tests and more idealized simulations, it was found that the features plausibly stem from vertical circulations set up by the terrain and maintained by the positive buoyancy gained downstream over the relatively warm water. Copyright c © 2011 Royal Meteorological Societ