Mechanisms in the development of anomalous sea ice extent in the western Arctic: A case study

Interannual cycles and trends in Arctic ice cover are dominated by strong r egional variability. Arctic sea ice extent exhibited a record minimum withi n the Arctic Basin during September 1990, dominated by a rapid retreat in t he Chukchi, East Siberian, and Laptev Seas. Simulations using a coupled reg ional model reproduced the enhanced cyclonic activity and enhanced ice melt which led to this large retreat in sea ice cover. Sensitivity experiments showed that accurate initial ice conditions are crucial for a realistic sim ulation of the ice anomaly, pointing to the need for adequate spin-up in co upled model experiments. It was also found that thermodynamic melt can acco unt for the bulk of the total loss in ice mass over the summer season in 19 90, but without dynamics, the spatial patterns characteristic of the ice re ductions are not reproduced well. Also, transport of ice was crucial to ini tiate the formation of the anomaly, even if the formation was delayed until later in the season. The ice-albedo feedback is important in allowing the continued formation of the ice anomaly throughout the summer. Interannual v ariations in atmospheric circulation that yield regional differences in ice thickness provide a preconditioning that significantly affected developmen t of the ice anomaly. This suggests that circulation modes play an importan t role in determining ice severity along the Siberian coast.