Mesoscale modelling of an off-ice flow in the Arctic marginal sea ice zone with different spatial resolution

Previous studies revealed difficulties of regional climate models over the Arctic to reproduce measured meteorological parameters and especially surface turbulent fluxes. One of the possible reasons for that is insufficient horizontal and vertical resolutions of such models. In order to investigate the effect of spatial resolution on the energy exchange between ocean and atmosphere, a case of an off-ice flow, a wind flow regime being typical for the Arctic marginal sea ice zone, was simulated. Two nonhydrostatic mesoscale models were used: NH3D and METRAS. Since the NH3D model was never used for simulating polar processes, the results of the control run of the NH3D model were validated against observational data for a cold-air outbreak observed in the region of the marginal ice zone north of Svalbard during an aircraft campaign carried out in spring 1993, and against the results of the METRAS model which is often used for Arctic atmospheric research. In numerical experiments with different horizontal and vertical resolutions, both the NH3D and METRAS models revealed the sensitivity of the modelled surface turbulent fluxes over open water to spatial resolution. The simultaneous use of coarser horizontal and vertical resolutions as being typical for regional climate models, resulted in about 10-15% change of turbulent sensible heat fluxes over the ice-free ocean. Our results suggest that even regional climate models using much higher resolution than large scale climate models might strongly under/overestimate the energy exchange between ocean and atmosphere during cold-air outbreaks.