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Interannual variations of snowmelt and refreeze timing on southeast-Alaskan icefields, U.S.A.

  • Joan M. Ramage (a1) and Bryan L. Isacks (a2)

Abstract

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 (T b) and diurnal-amplitude variations (DAV). Two types of melt regime have different summer characteristics. Onset is characterized by increasing average daily T b 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 T b throughout the melt season and return to low-amplitude DAV after melt onset. Refreeze on these pixels is identified by decrease in T b and accompanying high-amplitude DAV. Other pixels maintain high DAV throughout 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.

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References

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Journal of Glaciology
  • ISSN: 0022-1430
  • EISSN: 1727-5652
  • URL: /core/journals/journal-of-glaciology
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