MICROWAVE MELT SIGNATURES OF MID-LATITUDE MOUNTAIN GLACIERS

Mid-latitude, temperate mountain glaciers are a significant and dynamic repository of ice in the Coast Range of Alaska and in the Patagonian Andes. Both regions are characterized by significant year-round moisture and are difficult to access for field research. Microwave satellite observations now form a multi-decade, high temporal resolution record of surface conditions for these regions that can be used to understand glacier responses to climate. Glaciers in both regions span a range of climatic and topographic environments. Here we focus on the long term records of glacier melt from passive microwave sensors to assess the characteristics and variability of snow and ice melt on large icefields in these regions, specifically the Juneau and Stikine Icefields in North America and the Northern and Southern Patagonian Icefields in South America. The ~18-19 GHz and 36-37 GHz horizontally and vertically polarized bands of passive microwave sensors detect the frozen or unfrozen state of the glacier surface. Together, the Special Sensor Microwave Imager (SSM/I) records starting in 1987, followed by the Advanced Microwave Scanning Radiometer for Earth Observing Systems (AMSR-E) from 2002- present, make it possible to detect the timing and extent of snow melt and refreeze across both icefields at a daily timescale with a >20 year sequence of melt dynamics. Observations have a high temporal resolution (0.5 – 3 day) and low spatial resolution (12 - 25 km). Day and night observations show the spatial and temporal variability of melt and allow the characterization of monthly, seasonal, annual, and interannual patterns. Elevation, distance from the coast, and latitude affect the extent and timing of melt-refreeze cycles as detected by brightness temperature measurements (Tb). Melt tends to be seasonal east (inland) of the topographic divides, while the western (coastal) sides of the icefields are dominated by synoptic variability. These geographic and interannual melt signatures of each region are characterized by distinctly shaped Tb histograms.