The Role of Arctic Cold Lows in Generating Thin Ice Clouds: A Comparison between CloudSat-CALIPSO and NARCM Simulations

CloudSat and CALIPSO observations reveal two types of very extensive thin ice clouds in Polar regions: thin precipitating ice cloud layers (TIC-2) and lofted thin ice cloud layers of smaller crystals (TIC-1). The vertical distribution of the TIC-1 and TIC-2 clouds is the result of a combination of transport and microphysical processes experienced by the air mass along its trajectory. An important dynamical source of the vertical transport is the presence of dominant quasi-stationary cyclones known as cold lows over the Arctic Ocean. They originate from mid latitudes active storms that transported large amount of heat, moisture and aerosols into the high Arctic. Decaying cold lows produce slow adiabatic lifting of moisture and aerosol together, mixing aerosol 5 to 8 km deep into the arctic troposphere. The resulting stratified aerosol layers from these systems have been observed between 3 and 6 km forming with the cold air mass an aerosol dome across the Arctic basin. Their frequency and concentration often exceed that of most polluted region of the world at the same altitude. NARCM model simulations provide evidences that aerosols and water vapor are lifted together by cold low systems, from low level convergence in the Arctic atmosphere. This slow aerosol-cloud interaction over several days effectively allows for a dehydration-greenhouse feedback (DGF) process with implications on the Arctic climate. In this study, the role of cold lows and the significance of the Arctic thin ice clouds in relation to aerosols will be discused.