Extension of the Japan Aerospace Exploration Agency long-term Northern Hemisphere snow cover extent product beyond half a century

Abstract. The Japan Aerospace Exploration Agency (JAXA) has developed a long-term global snow cover dataset spanning 1978 to the present using a series of satellite-borne optical sensors. As the MODerate resolution Imaging Spectroradiometers (MODISs), one of the satellite sensors that have been in use, are scheduled to cease operation between late 2026 and early 2027, data from Visible Infrared Imager and Radiometer Suite (VIIRS) and Second generation GLobal Imager (SGLI) have been incorporated since April 2018 to ensure continuity of the record. Radiometric and geometric corrections were applied to VIIRS and SGLI using overlapping observations with MODIS, enabling consistent estimation of snow cover extent (SCE) including discrimination between dry and wet snow cover. The existing snow detection algorithm was retained, while additional cloud screening was introduced for SGLI to compensate for the absence of a mid-infrared band. Validation using in-situ snow depth and surface air temperature observations demonstrated stable SCE and wet snow cover extent accuracy from 1982 to 2024. Seasonal SCE biases remained below 1 %, indicating consistency with the MODIS-based product. The extended dataset reveals a significant long-term decline in Northern Hemisphere SCE, accompanied by pronounced regional and seasonal variability, while the summer wet snow cover fraction has increased. Snow cover duration has shortened significantly in western Eurasia, whereas trends in Asia and North America are weaker. Regularly updated for nearly five decades, the JAXA snow cover dataset provides a stable, consistent, and continuously extendable record for climate monitoring and long-term snow cover analysis.