Statistical and dynamical properties of ocean eddies in Fram Strait from spaceborne SAR observations

Abstract

Here we analyse high-resolution spaceborne synthetic aperture radar (SAR) measurements to retrieve statistical and dynamical properties of ocean eddies in the ice-free regions and the marginal ice zone (MIZ) of Fram Strait. Analysis of historical Envisat ASAR images allowes to obtain detailed spatial statistics of eddy generation sites, their diameters and vorticity sign. As shown, the total number of cyclones strongly dominates over anticyclones. Eddies are frequently observed over continental slope and shelf regions around Svalbard, however, about 80% of them are identified over the deep Fram Strait regions. In general, eddies range in size between 1.5 km and 64 km with a mean value of 8 km. Larger eddies of 10-30 km in diameter are usually found over deep water, while smaller eddies of 3-7 km in diameter prevail around Svalbard. As observed, the overall pattern of eddy field in the strait attributes well to the position of West Spitsbergen Current jet and its southern recirculation branch known from literature. Analysis of sequential Sentinel-1 images allows to retrieve surface current velocity field having a clear signature of an anticyclonic eddy in the Fram Strait marginal ice zone. Mean orbital velocity of the observed eddy is estimated to be around 0.4-0.5 m/s, in good agreement with earlier field observations. Presented results demonstrate the potential of spaceborne SAR data to retrieve critical properties of eddies of various scales, and further investigate their role in the Arctic Ocean.