Dynamic and Thermodynamic Characteristics of Atmospheric Response to Anomalous Sea-Ice Extent in the Sea of Okhotsk

Abstract

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. Significant response appears not only around the Sea of Okhotsk, but also downstream over the Bering Sea, Alaska, and North America in the form of a stationary wave train in the troposphere. This remote response, associated with wave activity flux emanating from the Okhotsk area to the downstream, is regarded as a stationary Rossby wave generated thermally by the anomalous turbulent heat fluxes from the ocean surface as a result of the anomalous sea-ice cover. The Pacific storm track in the model that extends zonally at 35°N is located too far south of the Sea of Okhotsk to exert substantial feedback forcing on the local and remote response. Since a similar stationary wave train is identified in the composite difference fields of the observed data between heavy and light ice years, it is believed 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 the thermal damping effect associated with the anomalous atmosphere–ocean heat exchange both in the model and real atmosphere.