Gap Flows in Nares Strait: Multi-Scale Numerical Model Simulations in Comparison to Aircraft Measurements

The steep topography of Ellesmere Island and the northern Greenland coast, combined with a stable boundary layer, generates intense low-level winds in Nares Strait, that influence sea ice transport. In Smith Sound, a gap flow forms impacting the most productive North Water Polynya. We use the non-hydrostatic regional climate model CCLM with horizontal resolutions of 14, 5 and 1 km to study these processes for the period of an aircraft-based experiment in June 2010. Additionally, CARRA reanalysis is included. All model data resolve the small channel and represent the stable boundary conditions realistically. The highest winds of around 14 m $s^{-1}$ are present in the exit region of Smith Sound for June 2010. Comparisons with aircraft profiles for potential temperature and wind speed show small biases and correlations higher than 0.84 for CCLM, along with a good representation of the boundary layer structure. Increasing model resolution from 14 to 5 km yields notable improvements in the representation of these variables. CARRA data are similar or better than CCLM data, except for the potential temperature, where a relatively large warm bias was found. Maximum winds occur at gap exit region of Smith Sound and are associated with gravity waves generated by the barrier, resulting in downward flow within the gap. Model simulations offer the advantage of studying the temporal development and the full three-dimensional structure. The wind maximum is influenced by the gap flow structure for mountain Froude numbers less than 1 and by the position and intensity of a low pressure system in Baffin Bay.