Cooperative Institute for Research in Environmental Sciences

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Spatial and Temporal Variability of Seasonally Frozen Ground in the Northern Hemisphere

Tingjun Zhang, Kevin Schaefer, James McCreight, and Richard Armstrong

NSIDC/CIRES

Changes in soil thermal regime and soil freeze/thaw cycle have significant impact on carbon exchange between the atmosphere and the land surface. Snow cover plays a critical role on soil thermal regime and soil freeze/thaw status in cold seasons/cold regions, thus has dramatically impact on ecosystem and carbon cycle as a whole. The ultimate goal of this study is to investigate spatial and temporal variability of seasonally frozen ground and snow cover in the Northern hemisphere and then to further study how changes in frozen ground and snow conditions influence ecosystem and carbon exchange. To archive this goal, we collected all available frozen ground and snow data from various sources and develop a comprehensive frozen ground and snow depth data time series over Northern Hemisphere. We have obtained in-situ snow depth and snow water equivalent (SWE) data from more than 6000 stations. We also obtained soil temperatures at various depths and soil freeze/thaw depth data from more than 2000 stations. Daily snow depth/SWE derived from passive microwave satellite remote sensing data from 1978 through 2005 were obtained from the National Snow and Ice Data Center, University of Colorado at Boulder. Using NSIDC frozen soil algorithm, daily area extent of near-surface soil freeze-thaw status was derived over the period from 1978-2005 using passive microwave satellite remote sensing data. Based on in-situ data at stations where both snow depth/SWE are available, we have obtained monthly snow density climatology and its standard deviation for five different snow types over North America. We further grided monthly snow density across NA with resolution of 25 km. Finally, we use daily snow depth/SWE from SMMR and SSM/I data as background and in-situ daily snow depth/SWE as control to generate a combined daily snow depth/SWE data product. We will conduct detailed analysis on their spatial and temporal variability in the past few decades over NH. We will present all details of frozen ground and snow products and discuss their potential applications for ecosystem and carbon exchange studies.