Wave flow simulations over Arctic leads

In this study, we have identified leads as sources of gravity waves. We have performed two-dimensional numerical simulations, using an advanced non-hydrostatic model (COAMPS), of idealized flow over ice with open water in the middle of the domain. We have simulated both a summer and two winter-cases with temperature differences of 3 and 27 K, respectively. The results show that the convective boundary layer that is created over the lead excite a standing gravity wave. The summer-case results are compared with theoretical calculations of flow over a ridge. Two winter-cases with background wind speeds of 2.5 and 5 m s-1 are studied. The downwind boundary layers are very different in these two cases and for the case with the higher wind speed the results show intermittency in turbulence above the boundary layer. The Arctic region is during long periods stably stratified from the ground and throughout the entire troposphere, giving possibilities for waves to propagate freely. Observations of surface fluxes in stable and very stably stratified boundary layers show that surface fluxes are not described very well by theories assuming local surface generated continuous turbulence. The magnitude of the wave from the single lead simulated here is small and comparable to a wave excited from a few meter high hill: the sea-ice contains ridges of these heights. These ice-ridges are, unlike the leads, not wide enough to excite internal gravity waves. Although small, considering the number of leads in the Arctic, these waves may still potentially interact with each other, increase in amplitude, break and contribute to surface turbulence. This would be a non-local intermittent source of near-surface turbulence.