Abstract
This research focuses on examining the spatial and vertical extent of low cloud cover changes that occur between April and May, using the 3S-GEOPROF-COMB data product. This globally gridded data product contains cloud vertical structure data fromthe CloudSat radar and CALIPSO lidar from 2006 to 2019. There is a substantial increase in low-level cloud cover between April and May over the entire Arctic Ocean, which is the most prominent over the Beaufort and Chukchi sea regions (70-82N, 120-180W). The April to May cloud cover increase only occurs in the low levels of the atmosphere (below 3.2 km) unlike in early autumn. Previous research has found that the early autumn cloud cover peak is strongly influenced by air-sea coupling, which leads to the most clouds forming over open waters at this time of year. Local air-sea coupling is not the cause of the April to May cloud surge since sea ice cover typically remains unchanged over the Arctic Ocean during this timeframe. This study finds that low-level stability decreases between April and May over many of the same regions that experience a cloud cover increase. There is a strong negative correlation between lowlevel stability and low-level cloud cover throughout the year in the Arctic, which underlies the importance of thermodynamics factors in regulating low cloud cover in the spring and throughout the year. In addition, there is a strong southerly wind reversal during May at 925 hPa (near the cloud layer) over western Canada and Siberia, which are regions that see a considerable increase in precipitable water values between April and May. Enhanced moisture advection from these regions might further saturate the cloud layer, allowing May cloud cover to maintain itself. The Beaufort High weakens and shifts west during May, which allows for low-level subsidence to decrease over the Beaufort Sea and explains why the May cloud cover surge is the most pronounced there.