Contributions of Atmospheric Transients to the Recent Changes in Summer Arctic Sea Ice Extent

We investigate the relationship between sea ice cover and lower troposphere heat and moisture transport associated with atmospheric transients of different frequencies during the melting season (May-September) in the Arctic. A large decrease in the September minimum sea ice extent has occurred in the last decade in a region extending from the Laptev Sea eastward toward the Beaufort Sea, and this decrease is a main contributor to the declining trend of September Arctic sea ice extent. We show that at the beginning of the melting season the interannual fluctuations in the poleward heat and moisture transport associated with both synoptic-scale (2-7 days) and low-frequency (10-30 days) atmospheric transient activity play a substantial role in determining the final minimum sea ice extent of individual seasons. They are also directly responsible for the initiation of seasons of extremely high and low sea ice extent. The synoptic and low-frequency atmospheric transients, with their weather manifestations being cyclones/anticyclones and atmospheric blocks/cut off lows, thus contribute significantly to the decadal-scale sea ice variability in the Arctic. The implications of these results for modeling and projecting future change in the Arctic climate system will be discussed.