HR: 0830h
AN: B31C-0323    [PDF]
TI: Trends in Pan-Arctic Springtime Thaw Monitored With Spaceborne Microwave Radiometry
AU: * McDonald, K C
EM: kyle.mcdonald@jpl.nasa.gov
AF: Jet Propulsion Lab, 4800 Oak Grove Drive, Pasadena, CA 91109-8099 United States
AU: Kimball, J S
EM: johnk@ntsg.umt.edu
AF: The University of Montana Flathead Lake Biological Station, 311 BioStation Lane, Polson, MT 59860 United States
AU: Njoku, E
EM: eni.njoku@jpl.nasa.gov
AF: Jet Propulsion Lab, 4800 Oak Grove Drive, Pasadena, CA 91109-8099 United States
AU: Running, S W
EM: swr@ntsg.umt.edu
AF: School of Forestry, The University of Montana, Missoula, MT 59812 United States
AB: 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. The size and remoteness of arctic and boreal ecosystems, however, pose a challenge to quantification of both terrestrial ecosystem processes and their feedbacks to regional and global climate conditions. Boreal and arctic regions form a complex land cover mosaic where vegetation structure, condition and distribution are strongly regulated by environmental factors such as moisture availability, permafrost, growing season length, disturbance and soil nutrients. The timing of spring thaw in particular, can influence boreal carbon uptake dramatically. With boreal forests accumulating 1% of their annual total accumulated carbon each day of the growing season, variability in timing of spring thaw can trigger total interannual variability in carbon uptake on the order of 30%. 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 utilize 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 determine the timing of the primary springtime thaw events across the pan-boreal high latitudes. 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.
DE: 0400 Biogeosciences
DE: 1600 GLOBAL CHANGE (New category)
DE: 1615 Biogeochemical processes (4805)
DE: 1640 Remote sensing
DE: 1863 Snow and ice (1827)
SC: Biogeosciences [B]
MN: 2003 Fall Meeting