Integrated pan-Arctic melt onset detection from satellite scatterometer and radiometer measurements

Satellite microwave and scatterometer measurements are very sensitive to the presence of liquid water in snow cover, and have been utilized to develop melt onset detection algorithms for various elements of the cryosphere. Given observed and predicted perturbations in the high latitude climate system as a result of global warming, an integrated pan-Arctic and pan-cryosphere melt onset and duration dataset is required to determine intra- and inter-seasonal variability in melt timing. In this study, we combine satellite derived melt onset estimates from unique, previously published, algorithms developed for the land surface, ice caps, large lakes, and sea ice. Backscatter threshold techniques were applied to scatterometer image reconstruction (SIR) QuikSCAT Ku-band backscatter measurements to retrieve melt parameters for terrestrial snow cover, lake ice, ice caps, and Canadian Arctic Archipelago sea ice. Melt onset outside the Archipelago was estimated with Special Sensor Microwave/Imager (SSM/I) passive microwave brightness temperatures. Evaluation of the integrated melt onset product shows the various algorithms perform consistently through the spring period. Some regional issues are apparent, such as conflicts in terrestrial versus ice cap melt onset (early interior versus late marginal onset) on some Eurasian islands because of differences in the melt detection algorithms for land snow and ice caps. Still, the integrated dataset illustrates regional variability in melt anomalies within and between seasons, and between cryospheric elements. Challenges remain in integrating melt duration due to dynamic processes associated with lake and sea ice that are absent on land, and distinguishing seasonal (snow, lake ice, first-year sea ice) from perennial components of the cryosphere (ice caps, multi-year sea ice).