Atmospheric Response to Observed Arctic Summer Sea Ice

It is generally accepted that changes in air temperature and circulation determine sea ice conditions, but it is not understood how the atmosphere is influenced by changes in sea ice. We employ the NCAR CCM 3.6 to investigate the atmospheric response to reduced sea ice.

A control experiment was integrated for 55 years by repeating the mean annual cycle of observed sea ice extent and SST, based on the period 1979-99. Sets of 51 member ensemble experiments were constructed by integrating the CCM from April to October using climatological SST and observed sea ice extent from the summer of 1995 (minimum).

Local as well as remote responses were found during the month of August. Above the region of reduced summer time sea ice, there is enhanced convection, lower sea level pressure, and warmer air temperatures penetrating deeply through the atmosphere. In addition, there is a significant downstream atmospheric circulation response, characterized by changes in precipitation and storm track intensity. The large scale response is characterized by anomalous high pressure in the north Pacific. Similar observed circulation patterns can be found during the August of 1995 as well as in a 16-case August slp composite based on reduced sea ice in the Kara Sea. The intriguing similarity between the model response and the observations will be discussed further.