Low opaque clouds formed over Baffin Sea enhances Greenland's west coast surface cloud warming

Greenland Ice Sheet (GrIS) melt plays a major role in the global sea level rise. Surface melting is driven by changes in the radiative budget at the surface which is modulated by clouds. However, relatively little is known on the influence of local atmospheric processes on the fragile GrIS coast. Here we used space based lidar cloud profile observations with complementary data to show that low clouds formed in response to the Arctic sea ice retreat in September are transported over the GrIS west coast and warm radiatively the GrIS surface. Previous works have shown that low liquid clouds are formed in response to arctic sea ice retreat in September. We first showed the existence of continuous stratiform low liquid clouds between the Baffin Sea and the GrIS west coast in September using 12 years space lidar data at full resolution (instantaneous time scale and less than 500m spatial scale). Secondly, we analyzed wind profiles from re-analyis and from recent Doppler wind space lidar data and found that westerlies transport these stratiform clouds from the Baffin Sea to the GrIS west coast. Then, we used Surface LongWave Cloud Radiative Effect data derived from space-based active sensors for days that correspond to these specific situations where clouds are transported from the Baffin Sea, to quantify how much they warm radiatively the GrIS coast. We found that clouds coming from the Baffin Sea warm radiatively the GrIS west coast surface by +80W/m2 during the month of September. This contributes to an increase of +10W/m2 of cloud surface warming in average between July and September on the GrIS west coast. Overall, this study suggests that processes independent from large-scale circulation also influence the GrIS mass balance.