Clear-Sky Cooling during Polar Night over the Sea Ice in the Arctic: The Role of Leads and Wind Speed.

We present a simple analytical model of the atmospheric boundary layer (ABL) over the sea ice during polar night in clear-sky conditions. The model represents coupling between the ABL and sea ice in the presence of leads. Both steady-state and time-dependent analytical solutions are obtained. The solutions describe air and surface temperatures as functions of many parameters among which are wind speed and sea ice concentration. In particular, analytical solution describes the transition from coupled to decoupled ABL state when wind speed is decreasing. Moreover, the model shows the stabilizing effect of leads on the ABL over the ice. Namely, it is demonstrated that leads might contribute to decoupling over the ice. Analytical solutions are compared to those of a more complex numerical single-column atmospheric model coupled to the thermodynamic model of the sea ice.

Also, observations from several recent Russian „North Pole“ drifting stations are used to demonstrate the sensitivity of the thermal regime over the sea ice to wind speed. The observations show that stronger wind speeds are associated with warmer temperatures, while for weak winds decoupling often occurs. Analytical solutions provide several possible explanations of the observed dependency of temperature on wind speed.