Data Information Page from ArcticRIMS (http://RIMS.unh.edu) Title: DAILY THAW DEPTH AND FROZEN GROUND DEPTH, Based on ERA-40 2-meter (Serreze, Oelke) Description: Daily thaw depth and frozen ground depth are calculated using a frozen ground model. Oelke et al. [2004] provide details, while also referring to [Oelke et al., 2003]. Thaw depth and frozen ground are calculated using different initial model settings. In the first case, all soil down to the lower model boundary is set to sub-freezing initial temperatures. Thawing during the summer months caused the development of a thawed layer at the top with the thaw depth again decreasing during freeze-up of the thawed layer in fall. Frozen ground depth on the other hand is calculated with soil temperatures at all depths above-freezing at the beginning. Here the frozen depth increased during winter, and spring thawing eventually decreases its value. Classification: Land Based, Climate Author/PI: Vorosmarty, Charles, Richard Lammers, Mark Serreze and Andrew Etringer Contact Information for original gridded daily time step data: Mark Serreze Senior Research Scientist 449 UCB, RL-2, #223 National Snow and Ice Data Center University of Colorado Boulder, CO 80309-0449 E-mail: serreze@kryos.colorado.edu Tel: 303-492-2963 Web: http://nsidc.org/research/bios/serreze.html Andrew Etringer National Snow and Ice Data Center CIRES, 449 UCB University of Colorado Boulder CO 80309-0449 USA E-Mail: etringer@nsdic.org Tel: 303-492-0784 Web: Contact Information for all spatially and temporally aggregated data in RIMS: Charles Vorosmarty Department of Civil Engineering The City College of New York Steinman Hall, Rm T-513 140th Street & Convent Ave, NY NY 10031 USA Email: cvorosmarty@ccny.cuny.edu Tel: (212) 650-7042 Web: http://crest.ccny.cuny.edu/ Richard Lammers Water Systems Analysis Group Institute for the Study of Earth, Oceans, and Space Morse Hall, Room 211 8 College Road University of New Hampshire Durham, NH 03824-3525 USA Email: Richard.Lammers@unh.edu Tel: (603) 862-4699 Web: http://www.wsag.unh.edu/ Temporal Coverage Begin Date (year-month-day): 1970-01-01 End Date (year-month-day): 2001-12-31 Spatial Coverage: Corner coordinates in Ease Projection (Units: Meters form N.P.) (Description at http://nsidc.org/data/ease/ease_grid.html) Minimum X: -4875633.612 m Minimum Y: -4875633.612 m Maximum X: 4875633.612 m Maximum Y: 4875633.612 m Corner coordinates in Geographical projection (Units: Degrees) (Description at http://en.wikipedia.org/wiki/Equirectangular_projection) Minimum latitude: 45.0 Minimum longitude: -180.0 Maximum latitude: 90.0 Maximum longitude: 180.0 Units: mm Aggregation Method: average General Methods: Thaw depth is calculated for areas identified from the International Permafrost Association (IPA) Circum-Arctic Map of Permafrost and Ground-Ice Conditions (IPA, 1998) as continuous permafrost, and for the frozen parts of discontinuous and sporadic permafrost. Thaw depth is not determined for non-permafrost (seasonally frozen ground) areas. The according model grid cell values are coded as missing (-9999.0). Frozen ground depth is calculated from the model for areas of seasonally frozen ground, and for the non-frozen parts of sporadic and discontinuous permafrost. No frozen ground depth is calculated for continuous permafrost areas (based on the IPA map). Again, the according grid cell values are coded as missing (-9999.0). Both thaw depth and frozen ground depth are simulated for the regions of discontinuous permafrost and for sporadic permafrost. For regions of continuous permafrost we only show simulated thaw depths whereas for seasonally frozen ground there is only frozen ground depth. zen Ground Model A finite-element model for one-dimensional heat conduction with phase change [Goodrich, 1982] is used. This model has been shown to provide excellent results for active layer depth and soil temperatures when driven with well-known boundary conditions and forcing parameters at specific locations. The model is applied to the entire Arctic drainage area (39926 grid cells) on the 25 km EASE-Grid with a daily time step. Soil is divided into three major layers (0-30 cm, 30-80 cm, and 80-3000 cm) with distinct thermal properties of frozen and thawed soil, respectively. Calculations are performed on 63 model nodes ranging from a thickness of 10 cm near the surface to 2 m at 30 m depth. Thermal properties of mineral soils are determined from soil dry bulk density and water content according to Kersten [1949] and Lunardini [1988] for peat. Initial temperatures are chosen according to the grid cell's permafrost classification based on the IPA map. The model is then spun up for 50 years in order to obtain more realistic start conditions for temperatures for all model layers. Frozen Ground Model - Details Active Layer Depth (ALD) in [cm], C. Oelke, A. Etringer, NSIDC, January 2005. ALD is calculated for the IPA areas of continuous, discontinuous, or sporadic/isolated permafrost. It applies to the frozen parts for discontinuous and sporadic/isolated permafrost. This output is from a simulation starting 1979-01-01, ending 2001-12-31 (8401 days), run in 4-year tiles with 1-year spinup for 1979-1982 and from a startup-file therafter. Missing values (-9999.0) apply for grid cells in seasonally-frozen areas. Active Layer Depth is produced at 39926 grid cells making up the entire Arctic drainage. Layers: 0-30 cm, 30-80 cm, 80-3000 cm. Temperature: ERA-40 2 meter Air Temperature on EASE-Grid [ECMWF, 2001]. Snow: modified Chang algorithm and climatology, 7-day maxima, no snow above 8 deg C. Snow density: Annual cycle for each of Sturm et al. (1995) snow classes (tundra, taiga, maritime, prairie, alpine): areas defined Sturm. Snow conductivity: Logarithmic fit to data of "others" in Sturm et al. (1997). Soil bulk density: From IGBP-DIS Soil Data System. Upper 2 soil layers (dens., cond.) modified with peat characteristics: density 500 kg/m**3, Peat conductivity for frozen and thawed cases from Lunardini (1988). Peat included dependent on topography (below 1200 m for layer 1, 1000 m for layer 2). Concentration of Clay+Silt and Sand+Gravel: From IGBP-DIS Soil Data System. Volumetric soil moisture: From UNH P/WBM climatology (1981-2000), redistributed from root and deep layers to the 3 model layers. Initialization: Temperature profiles dependent on the 3 permafrost classes; frozen. Climatological 20-year geothermal heat flux into lowest model layer. Temperature The model is driven by 2-meter air temperatures from the ERA-40 ECMWF Re-analysis [ECMWF, 2001]. The reanalysis data are provided on a N80 reduced gaussian grid. The data was regridded to a 25km Northern Hemisphere EASE-Grid using a bilinear inter- polation scheme [ECMWF, 2004]. Snow Cover Snow water equivalent (SWE) is derived from satellite passive microwave data. For the period 1978-1987, we use the retrieval algorithm of Chang et al. [1987] developed for the Scanning Multichannel Microwave Imager (SMMR). For the period 1988 onwards, coverage is provided by the Special Sensor Microwave/Imager (SSM/I). For the SSM/I period the retrieval algorithm was modified taking into account the different radiometer frequencies as compared to SMMR. Snow height is derived from SWE values by dividing by a climatological snow density at the given location and time of year. A 45-year time series of Canadian snow data (1955-1999) [MSC, 2000] is used to define the climatological seasonal cycles of snow density for tundra, taiga, prairie, alpine and maritime regions. These snow classes were defined by Sturm et al. [1995] based on climatological values of temperature, precipitation and wind speed. Tundra and taiga snow account for more than 90 % of the Arctic drainage area. Very thin snow cover often cannot be detected by passive microwave remote sensing because it does not provide a sufficiently strong scattering signal. Therefore, we also use the EASE-Grid version of the NOAA-NESDIS weekly snow charts [Armstrong and Brodzik, 2002] for snow identifica4tion. The NOAA charts are based on information from several visible-band satellites. For grid cells where the SSM/I does not detect snow but the NOAA charts do, we assume a snow thickness of 3 cm. The NOAA charts are most useful at the beginning of the winter season and for the southern margin of snow cover. Erroneous SSM/I depictions of snow, sometimes occurring in the middle of summer, are eliminated through comparison with the NOAA snow charts. Also of note, the maximum snow depth allowed is 80cm. Soil Properties Soil bulk density for the three major model layers is derived from the SoilData System of IGBP [Global Soil Data Task, 2000] that can generate maps of a number of soil parameters at user-selected depths and spatial resolution from their pedon data base. Since the SoilData System accounts only for mineral soil types, we parameterize a percentage of organic soil (peat) for the top two major soil layers [Oelke et al., 2003]. The relative compositions of clay, silt, sand and gravel for each grid cell are also extracted from the SoilData System. These concentrations are used to weight the different thermal conductivities for a) fine grained soils (clay and silt), and b) coarse grained soils (sand and gravel), calculated for frozen and thawed states [Kersten, 1949]. We input daily soil water content obtained from a 20-year model climatology (1981-2000) of the UNH Permafrost/Water Balance Model. Comments: Modeled thaw depths for sporadic permafrost areas, mainly in the southern parts of the Arctic drainage domain, are spuriously high. In these regions, the permafrost is very isolated and occurs at sub-grid scales. The forcing data sets (surface air temperature, snow cover, and soil bulk density) are likely not representative of the true forcing conditions for these small areas and produce an unrealistic increase of thaw depth with time. Frozen ground depths of small non-permafrost areas within discontinuous permafrost are likely too high as forcing parameters are more representative of the colder permafrost climate condition at these grid cells. References: Armstrong, R.L. and M.J. Brodzik, 2002: Northern Hemisphere EASE-Grid weekly snow cover and sea ice extent, Version 2. Boulder, CO, National Snow and Ice Data Center, CD-ROM. Chang, A.T.C., J.L. Foster and D.K. Hall, 1987: Nimbus-7 SMMR derived global snow cover parameters. Annals of Glaciology, 9, 39-44. European Centre for Medium-Range Weather Forecasts, 2002: ERA-40 Project Report Series. 3. Workshop on Re-analysis, 5-9 November 2001. European Center for Medium Range Weather Forecasts, 443 pp. European Centre for Medium-Range Weather Forecasts, 2004: website: Bilinear Interpolation Scheme. http://www.ecmwf.int/research/ifsdocs/CY25r1/Technical/Technical-3-04.html#wp961293 Global Soil Data Task, 2000: Global Gridded Surfaces of Selected Soil Characteristics (IGBP-DIS). International Geosphere-Biosphere Programme - Data and Information Services. Available online at [http://www.daac.ornl.gov] from the ORNL Distributed Active Archive Center, Oak Ridge National Laboratory, Oak Ridge, Tennessee, U.S.A. Goodrich, L.E., 1982: Efficient numerical technique for one-dimensional thermal problems with phase change. Int. J. of Heat and Mass Transfer, 21, 615-621. International Permafrost Association (IPA), 1998: Data and Information Working Group, Circumpolar Active-Layer Permafrost System (CAPS), version 1.0. Boulder, CO: National Snow and Ice Data Center/World Data Center for Glaciology, [CD-ROM]. Kersten, M.S., 1949: Laboratory research for the determination of the thermal properties of soils. Final report. Engineering Experiment Station, University of Minnesota. Lunardini, V.J., 1988: Heat conduction with freezing and thawing. US Army Corps of Engineers Cold Regions Research and Engineering Laboratory, Monograph, 88-1. Meteorological Service of Canada (MSC), 2000: Canadian Snow Data CD-ROM. CRYSYS Project, Climate Processes and Earth Observation Division, Meteorological Service of Canada, Downsview, Ontario, January 2000. Arctic RIMS Contact: Richard Lammers Water Systems Analysis Group Institute for the Study of Earth, Oceans, and Space Morse Hall University of New Hampshire Durham, NH 03824 Phone: (603) 862-4699 Fax: (603) 862-0587 Email: Richard.Lammers@unh.edu Web: http://wsag.unh.edu