Twice-daily satellite observations from the Special Sensor Microwave Imager (SSM/I) indicate melt onset and refreeze on southeast-Alaskan icefields. Melt and refreeze are based on 37 GHz vertically polarized brightness temperatures (Tb) and diurnal-amplitude variations (DAV). Two types of melt regime have different summer characteristics. Onset is characterized by increasing average daily Tb and a switch from low- to high-amplitude DAV.Melt timing, calibrated using Juneau Icefield temperatures, correlates well with nearby stream hydrographs. Some pixels maintain high Tb throughout the melt season and return to low-amplitude DAVafter melt onset. Refreeze on these pixels is identified by decrease in Tb and accompanying high-amplitude DAV.Other pixels maintain high DAVthroughout the summer, indicating nocturnal refreeze. Fall refreeze is determined by the end of high-amplitude DAV.Interannual variability in melt timing and ablation-season length is high. Melt onset and refreeze timing show a regional tendency toward earlier glacier-melt onset and longer ablation seasons from 1988-98.
The Journal of Glaciology is published six times per year. It accepts submissions from any discipline related to the study of snow and ice. All articles are peer reviewed. The Journal is included in the ISI Science Citation Index.