Mid-Latitude Atmospheric Responses to Arctic Sensible Heat Flux Anomalies in CCSM4

Abstract:

The rapidly diminishing Arctic sea ice cover impacts the overlying atmospheric state through changes in moisture and surface energy fluxes. These atmospheric responses may even reach the mid-latitudes; however, physical mechanisms linking Arctic change to mid-latitude weather remain unclear. We utilize present-day coupled general circulation model (GCM) output from NCAR’s Community Climate System Model, version 4 (CCSM4) to investigate the role of autumn sensible heat flux anomalies in forcing atmospheric responses in the Arctic and mid-latitudes. The self-organizing map (SOM) technique is used to characterize daily weekly-averaged sensible heat flux anomaly patterns over the Arctic. The atmospheric response is diagnosed by creating composites of atmospheric and sea ice variables (such as 2-m temperature, sea level pressure, geopotential height at various vertical levels, and sea ice thickness and concentration, for each heat flux pattern identified by the SOM technique from the Arctic to 30°N for each week for up to 12 weeks after a given pattern occurs) in order to identify the spatial patterns and temporal persistence required to force the remote atmospheric responses. A SOM pattern with prominent upward sensible heat fluxes extending from the Beaufort to Chukchi Seas exhibits a coherent progression of robust, anomalous downstream temperature and circulation responses, reaching the eastern United States about eight weeks after the initial heat flux anomaly. Persistent sea ice thicknesses may be important in forcing the atmospheric responses, highlighting the utility of using coupled GCM output and coupled systems reanalyses for observational studies.