Abstracts
SEARCH Open Science Meeting
October 27, 2003
Seattle, Washington, USA
Trends and Variability in Pan-Arctic Springtime Thaw Monitored with Spaceborne Microwave Remote Sensing
Kyle C. McDonald1, John S. Kimball2, Eni Njoku3, Steven W. Running4
1Terrestrial Science Research Element, Jet Propulsion Lab, Mail Stop 300-233, 4800 Oak Grove Drive, Pasadena, CA, 91001, USA, Phone 818-354-3263, Fax 818-354-9476, kyle.mcdonald@jpl.nasa.gov
2Flathead Lake Biological Station, University of Montana, 311 BioStation Lane, Polson, MT, 59860, USA, Phone 406-982-3301, Fax 406-982-3302, johnk@ntsg.umt.edu
3Terrestrial Science Research Element, Jet Propulsion Lab, Mail Stop 300-233, 4800 Oak Grove Drive, Pasadena, CA, 91001, USA, Phone 818-354-3693, Fax 818-354-9476, eni.g.njuku@jpl.nasa.gov
4NTSG, College of Forestry and Conservation, University of Montana, Missoula, MT, 59812, USA, Phone 406-243-6311, Fax 406-243-4510, swr@ntsg.umt.edu
Land surface seasonal transitions between predominantly frozen and thawed conditions occur each year over roughly 50 million square kilometers of Earth's Northern Hemisphere, profoundly affecting surface meteorological conditions, ecological trace gas dynamics, and hydrologic activity. Spatial and temporal variability in the timing of spring thaw is a major driver of regional vegetation activity and net carbon exchange with the atmosphere at high northern latitudes.
The ability to quantifiably apply multi-year observations of landscape freeze-thaw status of 1- to 2-day temporal fidelity to ecosystem process studies in high-latitude regions will allow improved assessment of modeled processes for long-term monitoring. We employ radar backscatter measurements from the SeaWinds-on-QuikSCAT scatterometer and brightness temperature measurements from the Special Sensor Microwave Imager (SSM/I) and the Scanning Multichannel Microwave Radiometer (SMMR) to examine trends in the timing of springtime thaw across the pan-boreal high latitudes since 1979. We apply a temporal discrimination technique to these data sets to examine the timing of significant springtime thaw events across the pan-Arctic basin and Alaska. We apply data from biophysical monitoring stations to quantify the sensitivity to surface freeze-thaw state transitions and associated vegetation biophysical processes under a variety of terrain and landcover conditions. We develop a time series of landscape freeze-thaw products at regional and pan-boreal scales across multiple years. These time series products demonstrate the highly complex spatial and temporal nature associated with these critical processes.
Results show a trend toward an advance in pan-boreal springtime thaw over the past years, corroborating similar findings relating to advance in vegetation green-up. The continued capability for monitoring seasonal freeze-thaw cycles across the pan-boreal region provides a means for assessing interannual variability and, eventually, longer-term trends in ecosystem function.
This work was performed at the Jet Propulsion Laboratory, California Institute of Technology, and the University of Montana under contract with the National Aeronautics and Space Administration.
Abstract Categories: Changes on Land
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