Combining in situ observations and remote sensing data to determine the spatial extent of rain-on-snow events on the Brøgger peninsula

Kurzfassung

Climate change is particularly impacting the Arctic, where the temperature increase is stronger than the global mean due to Arctic Amplification. Long-term observations at sites such as Ny-Alesund on the Brøgger’s peninsula in Svalbard allow understanding meteorological changes taking place in the Arctic. In the last decades, Ny Alesund was affected by a large increase of winter temperatures leading to occasional periods of positive temperatures lasting few days. As a result, the number of rainfall events also increased, contributing to an early degradation of the snowpack on the Brogger peninsula. Meteorological measurements such as at Ny Alesund allow to quantify the temporal variability of these “rain on snow” (ROS) events at specific points. The goal of this study is (i) to spatialize recent ROS events on the Brøgger peninsula during the period 2019-2022 using remote sensing radar data and (ii) to characterize the atmospheric origin of these events using anomalies of 500 hPa height or the identification of cyclonic systems. We use SAR satellite images from each event, mainly TSX and RCM images provided by German and Canadian Space Agencies. We processed the images with a thresholding method in order to find the spatial elevation limits between wet and dry snow after the events. PlanetScope optical images are used for snow extent validation. During the ROS episodes, the snow remains generally dry upstream of the glaciers, while at lower altitudes the snow on the peninsula is systematically wet. These ROS episodes are associated to cyclonic systems originated from the Northern Atlantic Ocean, and to a strong Z500 gradient from high pressure centered in Norway and low pressure centered in Greenland. These results are important to better characterize the origins and the spatial variability of ROS events and to evaluate the impact of these specific events on glaciers, permafrost, or ecology.