Date of this Version
Snow melt onset is defined as the point in time when the appearance of liquid water in the snow pack changes the crystalline structure within the pack. Owing to the associated increase in surface albedo during melt, surface energy absorption increases rapidly after the onset of snow melt. Monitoring interannual variations in snow melt onset is therefore useful for accurately modeling surface conditions, and it is also valuable for validating climate models and detecting climate change. Since microwave emission changes rapidly when liquid water appears in the snow pack, passive microwave remote sensing techniques can monitor melt onset. Passive microwave satellite data from the Scanning Multichannel Microwave Radiometer (SMMR) and the Special Sensor Microwave/Imager (SSM/I) are indispensable for this task because they represent an all-season, all-weather, diurnally consistent, and reasonably continuous data set for more than 20 years in length (1979-1998). The microwave data time series is created from a blended brightness temperature record generated from different satellite platforms through linear regression analysis to ensure consistency in the data set. The melt onset date is calculated by monitoring the difference between the 18-GHz (SMMR) or 19-GHz (SSM/I) horizontal brightness temperatures and 37-GHz horizontal brightness temperatures. Results indicate both regional and annual variations exist in the melt onset dates. The melt onset dates are generated annually and are available via ftp from the National Snow and Ice Data Center (NSIDC). This new data set provides a valuable addition to researchers for seasonal-to-interannual and long-term climate studies, and it is hoped that others will find the data set useful.