Advances in seasonal snow water equivalent (SWE) retrieval using in situ passive microwave measurements over first‐year sea ice

Abstract

Dramatic changes have occurred in the Arctic over the past three decades in response to an accelerated warming that will have a significant impact on the world's climate. Snow accumulation (measured as snow water equivalent, SWE) over sea ice plays a key role in the changes observed due to its effect on the surface energy balance that dictates the timing of sea‐ice freeze‐up and decay. Increased awareness of the role of snow in the Arctic system has triggered numerous studies that have attempted to characterize snow accumulation from space since the early 1980s, but none has successfully quantified SWE on a seasonal basis. This work presents the first seasonally valid SWE algorithm for first‐year sea ice based on in situ passive microwave radiometry. The in situ data were collected as a part of the Canadian Arctic Shelf Exchange Study (CASES) during the overwintering mission of the Canadian Coast Guard Ship (CCGS) Amundsen in 2003–2004. Previous work clearly demonstrated two different patterns of seasonal snow evolution, for which the algorithm presented in this paper accounts for. Our algorithm's results are valid for temperatures between −5 and −30°C and SWE in the range of 0–55 mm. Results show that the behaviour of the snow's thermophysical properties and brightness temperatures (T b) is quite different in the winter cooling period compared with that in the warming period, where temperature gradient metamorphism begins at a SWE value of 33 mm. The SWE algorithm successfully models this change with a high degree of correlation.