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Determination of melt-onset and refreeze timing on southeast Alaskan icefields using SSM/I diurnal amplitude variations

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Abstract:

Timing of snowmelt and freeze-up was estimated for glaciers in the Coast and St Elias Ranges of Alaska, U.S.A., and British Columbia, Canada, using twice-daily brightness temperatures (Tb) from the U.S. Defense Meteorological Satellite Program's Special Sensor Microwave/Imager (SSM/I). Melt and freeze-up were determined for a 37 GHz vertically polarized time series using changes in the average daily Tb and high-amplitude Tb diurnal amplitude variations (DAV). DAV are the running difference between the early-morning (usually minimum) and late-afternoon (usually maximum) Tb observations. Year-round temperatures taken at 2 hour intervals on the Juneau Icefield (58°4' N, 134°15' W) validated the microwave response to melt. A bimodal distribution of Tb corresponding to frozen or melting snow helped estimate the Tb at which the transition from frozen to melting snow occurred on pixels without ground observations. Thresholds of Tb (>246 K) and DAV (>±10 K) were used to refine the selection of melt and refreeze timing for southeast Alaska. Melt timing correlates with stream discharge. In general, melt onset occurred progressively earlier and refreeze later in the season between 1988 and 1998. It is not known whether this is related to regional warming or to one of the shorter decadal-scale oscillations in the Gulf of Alaska.

Document Type: Research Article

DOI: https://doi.org/10.3189/172756402781817761

Publication date: 2002-01-01

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  • The Annals of Glaciology is a peer-reviewed, thematic journal published 2 to 4 times a year by the International Glaciological Society (IGS). Publication frequency is determined and volume/issue numbers assigned by the IGS Council on a year-to-year basis and with a lead time of 3 to 4 years. The Annals of Glaciology is included in the ISI Science Citation Index from volume 50, number 50 onwards.

    Themes can be on any aspect of the study of snow and ice. Individual members can make a suggestion for a theme for an Annals issue to the Secretary General, who will forward it to the IGS Publications Committee. The IGS Publication Committee will make a recommendation for an individual themed Annals issue, together with a potential Annals Chief Editor for that issue, to IGS Council. The IGS Council will make the decision whether to proceed, taking into account the spread of topics and the overall capacity for publication of pages in Annals.

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