Melt Patterns and Dynamics in Alaska and Patagonia Derived from Passive Microwave Brightness Temperatures

Kathryn Semmens,Joan Ramage

doi:10.3390/rs6010603

Abstract

Glaciers and icefields are critical components of Earth’s cryosphere to study and monitor for understanding the effects of a changing climate. To provide a regional perspective of glacier melt dynamics for the past several decades, brightness temperatures (Tb) from the passive microwave sensor Special Sensor Microwave Imager (SSM/I) were used to characterize melt regime patterns over large glacierized areas in Alaska and Patagonia. The distinctness of the melt signal at 37V-GHz and the ability to acquire daily data regardless of clouds or darkness make the dataset ideal for studying melt dynamics in both hemispheres. A 24-year (1988–2011) time series of annual Tb histograms was constructed to (1) characterize and assess temporal and spatial trends in melt patterns, (2) determine years of anomalous Tb distribution, and (3) investigate potential contributing factors. Distance from coast and temperature were key factors influencing melt. Years of high percentage of positive Tb anomalies were associated with relatively higher stream discharge (e.g., Copper and Mendenhall Rivers, Alaska, USA and Rio Baker, Chile). The characterization of melt over broad spatial domains and a multi-decadal time period offers a more comprehensive picture of the changing cryosphere and provides a baseline from which to assess future change.

Highlights

Melt dynamics of glaciers and icefields respond to weather, and collectively over the long-term can be indicators of a changing regional climate
We address the questions: Do melt regime pattern and evolution vary according to climatology, distance from coast and elevation?
Alaska has a wider distribution of melt regime types ranging from the warmer/wetter asymmetric high and bimodal high distributions to the colder/frozen even and bimodal low distributions farther inland and at higher elevations

Summary

Introduction

Melt dynamics of glaciers and icefields respond to weather, and collectively over the long-term can be indicators of a changing regional climate. Two areas of rapid change are glaciers and icefields in Alaska [2] and Patagonia [3,4]. Glaciers, consisting of coastal, temperate, tidewater, and glacierized mountain ranges, cover about 75,000 km of Alaska with an elevation range up to 6,000 m [5]. In Alaska, the average air temperature increase is on the order of 2 °C since the mid-20th century [6]. The 20th century warming coincides with glacier retreat and thinning (for glaciers ending below 1,500 m elevation), and stagnation (for higher elevation glaciers) found at all mountain ranges and island groups in Alaska [5]

Results

Discussion

Conclusion