A Case Study of Regional Climate Anomalies in the Arctic: Performance Requirements for a Coupled Model

Abstract

Simulations of Arctic climate require treatment of land, ocean, ice, and atmospheric processes, and are further complicated by the dynamic nature of the sea ice cover. Here, the ability of a climate system model to simulate conditions over the Arctic Ocean during April?September 1990, a period of anomalous atmospheric circulation and sea ice conditions, is investigated. Differences between observations and model results are used to gain insight into the mechanisms that contributed to the observed record reduction in ice extent in late summer. The coupled model reproduces the general patterns seen in comparison sea level pressure fields in most months, but the discrepancies significantly affect the model?s ability to simulate details of sea ice transport and warm air advection linked to the unusual ice conditions. The use of prescribed sea ice fraction in the climate model yields relatively small changes in the surface energy balance compared to the fully-coupled simulation with dynamic ice cover, but significantly affects atmospheric circulation in spring and late summer. Analyses of observations, coupled model experiments, and stand-alone ice model output suggest a positive feedback between ice dynamics and ice melt that contributed to the ice extent anomaly. The results highlight the importance of regional atmospheric circulation in driving interannual variations in Arctic ice extent, and illustrate the level of model performance needed to simulate such variations.