The Temporal and Spatial Evolution of Atmospheric Responses to Changing Arctic Ice Cover in CCSM4

Catrin M. Mills, John J. Cassano, and Elizabeth N. Cassano

Abstract
The rapidly diminishing Arctic sea ice cover impacts the overlying atmospheric state through changes in moisture and surface energy fluxes, and the spatial extent of this atmospheric response remains unclear and may even reach the mid-latitudes. Synoptic atmospheric responses to surface sensible heat flux anomalies over the Arctic Ocean during autumn (SON) in the present-day climate (1974 – 2005) of NCAR’s Community Climate System Model, version 4 (CCSM4) are investigated. The self-organizing map (SOM) technique is used to characterize important daily running-weekly-mean surface heat flux anomaly patterns over the Arctic. The importance of the week-to-week persistence and spatial extent of the surface heat flux anomalies in forcing the atmospheric response is diagnosed by creating composites of atmospheric variables (such as 2-m temperature, sea level pressure, and geopotential height at 850, 500, and 250 hPa) for each heat flux pattern identified by the SOM technique from the Arctic to 20°N for each week, up to 12 weeks, in order to identify the temporal persistence required to force the remote atmospheric responses.