Submesoscale physical processes in the atmospheric boundary layer above fragmented sea ice.

In consequence of sea ice fragmentation in winter a range of physical processes take place between the sea/sea ice and the atmospheric boundary layer (ABL). Most of them occur on the level of individual ice floes and cracks and thus cannot be directly resolved by numerical weather prediction (NWP) models.  Parametrizations of those processes aim to describe their overall effect on grid scale values, given the grid scale variables. However, as many of the processes taking place during winter sea ice fragmentation remain largely unrecognized they cannot be incorporated into the NWP models. 

The aim of the presented study is to determine whether the floe size distribution (FSD) has an effect on the ABL. Our previous research (Wenta, Herman 2018 and 2019) indicates that FSD might determine the intensity and spatial arrangement of convection and heat fluxes. A coefficient has been proposed for the correction of moisture heat flux, which can be incorporated into the NWP models. However, this research is based entirely on idealized model simulations and requires further modelling and observations based studies.

In order to address this shortcoming, a field campaign is going to take place in the Bay of Bothnia in March 2020. Our goal is to create a 3D view of the atmosphere above fragmented sea and verify whether the processes and effects we found in the modeling results take similar form in real situations. Measurements results will be useful in the validation of our numerical modelling studies and will provide a unique dataset about the sea-ice-atmosphere interactions in the Bay of Bothnia area. Considering a significant decreasing trend in winter sea ice extent in the Baltic Sea it might contribute to our understanding of the role of ice in the local weather patterns. The field campaign is going to be complemented by numerical modelling with full version of Weather Research and Forecasting (WRF) model adjusted to the conditions over the Bay of Bothnia. 

Combined together - the results of our previous modelling studies and the results from the Bay of Bothnia field campaign, may considerably increase our knowledge about the surface-atmosphere coupling in the event of winter sea ice fragmentation.