Summary

The seasonal transition of the land surface from a frozen to thawed state represents the closest analog to a biospheric on/off switch existing in nature, initiating a number of terrestrial processes that are virtually dormant under frozen conditions. Landscape freeze/thaw transitions coincide with marked shifts in albedo, surface energy and mass exchange, including ecological trace gas, snow and river runoff dynamics. This abrupt state transition occurs each year over roughly 50 million km2 of the Earth's terrestrial surface. In any given year, the timing of seasonal thaw can vary by up to 6 weeks or more with significant impacts on biogeochemistry. Globally, average temperatures are currently undergoing a period of warming, especially at high latitude boreal and arctic regions; this warming is currently expected to continue over this century from 1-3.5°C above current conditions. If the timing and/or areal extent of this state transition were to change significantly, measurable changes in climatic, hydrologic and ecological processes would result.

Our current abilities to monitor these processes in high latitude boreal and arctic regions are severely limited by the enormous size and remoteness of the region, adverse environmental conditions, and the sparse regional surface weather station network. Our research is finding that satellite based radar techniques are particularly well-suited to quantifying this freeze/thaw transition over broad landscapes, due to specific molecular features of how radar wavelengths interact with polar water molecules in solid and liquid states. We are currently developing new methods and technologies for quantifying the land surface freeze/thaw transition regionally by satellite, for operational monitoring of this significant high latitude phenomenon.

Please see recent E-Newsletters concerning this research at the sites below:

The Jet Propulsion Laboratory's Spotlight Features Web Site.
The Earth Observatory Newsroom Web Site.