SATELLITE OBSERVATION AND CLIMATE SYSTEM MODEL SIMULATION OF THE ST-LAWRENCE ISLAND POLYNYA

The St. Lawrence Island polynya (SLIP) is a commonly occurring winter phenomenon in the Bering Sea, in which dense saline water produced dur ing new ice formation is thought to flow northward through the Bering Strait to help maintain the Arctic Ocean halocline. Winter darkness an d inclement weather conditions have made continuous in situ and remote observation of this polynya difficult. However, imagery acquired from the European Space Agency ERS-1 Synthetic Aperture Radar (SAR) has al lowed observation of the St. Lawrence Island polynya using both the im agery and derived ice displacement products. With the development of A RCSyM, a high resolution regional model of the Arctic atmosphere/sea i ce system, simulation of the SLIP in a climate model is now possible. Intercomparisons between remotely sensed products and simulations can lead to additional insight into the SLIP formation process. Low resolu tion SAR, SSM/I and AVHRR infrared imagery for the St. Lawrence Island region are compared with the results of a model simulation for the pe riod of 24-27 February 1992. The imagery illustrates a polynya event ( polynya opening). With the northerly winds strong and consistent over several days, the coupled model captures the SLIP event with moderate accuracy. However, the introduction of a stability dependent atmospher e-ice drag coefficient, which allows feedbacks between atmospheric sta bility, open water, and air-ice drag, produces a more accurate simulat ion of the SLIP in comparison to satellite imagery. Model experiments show that the polynya event is forced primarily by changes in atmosphe ric circulation followed by persistent favorable conditions: ocean sur face currents are found to have a small but positive impact on the sim ulation which is enhanced when wind forcing is weak or variable.