The Driving of Intraseasonal Winter Sea Ice Decline over the Barents and Kara Seas

In this study, the contributions to intraseasonal sea ice decline over the Barents and Kara Seas (BKS) by increased surface downward infrared radiation (IR) and enhanced sea ice motion are examined. For this purpose, sea ice decline events are sorted into strong and weak evaporation categories, defined by the strength of the evaporation at positive lags. European Centre for Medium-Range Weather Forecasts Re-Analysis (ERA-Interim) data is used for the winter season (December–February) for the years of 1979–2012. For both types of events, a toy model is used to estimate the reduction in sea ice thickness due to changes in surface downward IR and wind-driven sea ice motion. For the strong evaporation events, both increased surface downward IR and enhanced wind-driven sea ice motion contribute to the sea ice decline, with the impact of the former being larger. For the weak evaporation events, it is found that the sea ice decline is almost entirely due to an increase in surface downward IR. It is found that sea ice decline with strong evaporation is associated with a westward propagating zonal wave number 1 disturbance in high latitudes, whereas sea ice decline with weak evaporation is characterized by a quasi-stationary wave pattern that includes a Ural-block-like feature.

The increase in surface downward IR associated with rapid, intraseasonal sea ice loss over the BKS is shown to arise from the intrusion of warm, moist air from midlatitudes into the Arctic. For most days during both types of events, it is found that the anomalous sensible and latent heat fluxes are downward. It is only for a brief period of 2-3 days that the anomalous sensible and latent heat fluxes are upward. These upward surface fluxes arise from the advection of cold, dry air over those parts of the BKS which have become free of sea ice, following the warm, moist air intrusions. The implication of this result is that at the instraseasonal time the melting of sea ice in the BKS has little influence on the midlatitude circulation.