| The Southern Patagonian Icefield (SPI) straddles the Andes Mountains between Argentina and Chile, and covers 13,000 km2. Passive microwave observations from the Advanced Microwave Scanning Radiometer for Earth Observing Systems (AMSR-E) make it possible to monitor the extent and timing of melting and refreezing. AMSR-E captures both frozen and wet snow surface features because the presence of liquid water dramatically changes the emissivity of snow. Over the SPI the diversity of climatic and topographic environments motivates this exploration into the spatial variability of melt timing and extent. Histograms of brightness temperature measurements (Tb) in the 37 GHz vertically polarized (V) channel display distinct melt regimes on the windward and leeward side of the Andes. East of the divide melt extent, timing, and duration respond to temperature. Elevation, position on the Andean divide, and latitude affect the extent, timing, frequency, and magnitude of Tb indicative of melt and melt-refreeze cycles. Using the established 252 K Tb and diel Tb contrast, DAV thresholds of 18 K in the 37 V channel and 5 K in the 19 GHz V channel, melt onset is the first occurrence where these conditions are met. Both 19 V and 37 V channels show interannual plots trending towards a later melt onset date. "Sustained melting" begins when the minimum Tb value exceeds 252 K six out of seven consecutive days. The 19 V and 37 V interannual results of sustained melt onset trend towards an earlier date except in the northwest sector. Regional melt onset dates were related to peak streamflow dates recorded at the Santa Cruz at Charles Fuhr gauge. Six pixels in the basin show significant relationships with mean lagtimes between 195-234 days. Pixels closer to the gauging station have shorter lagtimes, 132-187 days, than those farther away, 195-234 days. The AMSR-E signal is seasonal but short-term synoptic variability superimposes it. Annual and seasonal glacier mass balance indicators, such as the spatial distribution of surface melt, melt timing, and its relationship to runoff timing will assist further analysis and modeling efforts to quantify changes in the volumetric loss rates for all large temperate glacial systems. |
