Interannual variability of the Storfjorden (Svalbard) ice cover and ice production observed by ERS-2 SAR

The storfjorden (Svalbard) ice cover has been observed via European remote-sensing satellite (ERS-2) synthetic aperture radar (SAR) over two winters from 1997 to 1999 that showed a high interannual variability in atmospheric forcing. This has resulted in different scenarios in the formation of the ice cover. We reconstruct the ice-cover evolution with a simple ice-drift and polynya model consistent in parameterization for both winters and with ERS-2 SAR and ground-truth observations. The observations showed that during the rather cold winter of 1997/98, a fast-ice cover developed over the whole northern part of Storfjorden that closed the ice advection through two sounds. A polynya of up to 6000 km(2) developed persistently under northerly winds. The mild winter of 1998/99 showed a different pattern in the Storfjorden ice cover: the fast-ice extent was reduced to the coastal region, so ice motion was more important than in the previous winter. A larger thin-ice and open-water area over the whole fjord resulted in lower total ice production but relocated the strong ice production sites to shallower waters. Thus, freezing in a large region of shallow waters in the north of Storfjorden in 1998/99 produced denser waters than freezing in a smaller polynya over the deeper centre of Storfjorden during the colder winter 1997/98.