Influences of Atmospheric Eddies on the Initial Melt of Arctic Sea Ice: The Role of Cloud Fraction Anomalies and Poleward Heat Transport by High- and Low-Frequency Atmospheric Eddies

Accompanying the well-documented decline in September minimum Arctic sea ice extent has been an increase in the length of the Arctic sea ice melt season, with a trend toward an earlier initial melt and later freeze-up. Previous studies have hypothesized that early initial melt contributes to the decline in September minimum sea ice extent. In this research, we explore the relationship between atmospheric variability and the initial melt date of Arctic sea ice, focusing on the contribution of atmospheric eddy meridional heat transport and the contribution of surface longwave and shortwave radiation anomalies linked to the associated eddy-generated cloud fraction anomalies. Total and eddy components of meridional heat transport across the polar cap boundary are calculated from reanalysis data, and surface radiation data is acquired from the NASA Clouds and the Earth's Radiant Energy System (CERES) project dataset. We classify the eddy components of the meridional heat transport by frequency into high-, low-, and seasonal-scale eddies. The decline in the mean initial melt date is primarily found in a region bounded by 90°E and 130°W longitude, which corresponds to the Laptev, East Siberian, Chukchi, and Beaufort Seas. The decline in this region is not associated with an increase in the sum of meridional heat transport during the melt season, rather it is characterized by episodes of initial melt covering a large area. In an investigation of two of these melt episodes, a positive total meridional heat transport by high-frequency eddy winds is associated with the peak melt. Additionally, there is a positive anomaly in surface downwelling shortwave radiation collocated with the peak initial melt, likely related to a lack of cloud cover.