Influence of sea-ice extent anomalies within the Sea of Okhotsk on the large-scale atmospheric circulation is investigated through an analysis of the dynamic and thermodynamic characteristics of the response in an atmospheric general circulation model to specified anomalous sea-ice cover. In a response to heavy Okhotsk ice cover, an anomalous surface cold high appears over the ice-covered Okhotsk and the Aleutian low develops over the southern Bering Sea. In a simulation for light Okhotsk ice cover, the cold high over the Okhotsk weakens and the Aleutian low also weakens and is split into two cells. Furthermore, the difference fields obtained by subtracting the model responses for the light-ice simulation from the heavy-ice ones indicate that significant wave-like anomalies extend downstream over the Bering Sea, Alaska and North America roughly along a great circle that passes the Sea of Okhotsk. Similar wave-like anomalies are evident also in the middle and upper troposphere in the form of a stationary wavetrain. This atmospheric remote response is regarded as a stationary Rossby wave generated thermally through the anomalous surface heat fluxes from the ocean surface as a result of the anomalous sea-ice cover, because wave activity flux emanates from the lowest layer over the Okhotsk upward and then to the downstream. The Pacific stormtrack in the model that extends zonally at 35°N is located too far south of the Sea of Okhotsk to exert substantial feedback forcing in the local and remote response. Since a similar stationary wavetrain is identified in the composite difference fields of the observed data between heavy and light ice years, we believe that the model appropriately reproduces the real atmospheric response to the Okhotsk sea-ice extent anomalies. Simulated seesaws in the meridional surface wind and surface air temperature anomalies between the eastern Sea of Okhotsk and eastern Bering Sea associated with the local and remote response, respectively, to the Okhotsk sea-ice anomalies seem to be consistent with the observed seesaw in the anomalous sea-ice cover between these maritime regions. There is a hint of reinforcement of the remote response around the Alaskan Pacific coast through destabilization of barotropic Rossby waves due to thermal damping effect associated with the anomalous atmosphere-ocean heat exchange both in the model and real atmosphere.
Close window or click on previous window to return to the Conference Program.
12th Conference on Atmospheric and Oceanic Fluid Dynamics