Time-series analysis of passive-microwave-derived central North American snow water equivalent imagery

Abstract

The Meteorological Service of Canada has developed a series of operational snow water equivalent (SWE) retrieval algorithms for central Canada, based on the vertically polarized difference index for the 19 and 37 GHz channels of the Special Sensor Microwave/Imager (SSM/I). Separate algorithms derive SWE for open environments, deciduous, coniferous and sparse forest cover. A final SWE value represents the area-weighted average based on the proportional land cover within each pixel. In this study, 5 day averaged (pentad) passive-microwave-derived SWE imagery for the winter season (December–February) of 1994/95 is compared to in situ data from central Canada in order to assess algorithm performance. Investigation of regions with varying proportional land cover within the four algorithm classes shows that retrieved SWE remains within ±10–20mm of surface observations, independent of fractional within-pixel land cover. Following algorithm evaluation, ten winter seasons (1988/89 through 1997/98) of pentad central North American SWE imagery are subjected to a rotated principal-component analysis (PCA). Although there are no trends in total study-area SWE, the PCA results identify the interseasonal variability in the SWE accumulation and ablation centers of action through the SSM/I time series.