Merging Conventional (1915–92) and Passive Microwave (1978–2002) Estimates of Snow Extent and Water Equivalent over Central North America

Abstract

A detailed evaluation of snow water equivalent (SWE) and snow cover extent (SCE) derived using the combined Scanning Multichannel Microwave Radiometer (SMMR) and Special Sensor Microwave Imager (SSM/I) brightness temperature records for the 1978?2002 period was carried out for a longitudinal transect in the continental interior of North America. Comparison with in situ SWE observations showed that the SMMR brightness temperature adjustments are required to produce SWE retrievals with similar bias and rmse as observed during the SSM/I period. Underestimation of SCE in the passive microwave dataset (relative to NOAA snow charts) was identified as a systematic problem, most pronounced in early winter and during seasons with above-average snow extent. The passive microwave data were successfully merged with historical data based on strong interdataset agreement for a 1978?92 overlap period. Analysis of SWE and SCE time series for the months of December through March 1915?2002 provided information on SWE and SCE variability over the interior of North America, but yielded no evidence of significant trends in either variable over the 88-yr period. Anomalies observed during the relatively recent period of passive microwave data acquisition did not exceed the range of anomalies observed in the historical data record.