Jason Box Datasets
From Byrd Polar Research Center
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[edit] Data Sets
- Greenland Land Surface Classification Mask
- Greenland Accumulation Grids
- Greenland Ice Sheet Surface Mass Balance Data
[edit] Greenland Land Surface Classification Mask
1.25 km x 1.25 km (equal area) grid cells are classified as land or sea using NDVI and NDSI thresholds applied in daily 21 June - 15 September (end of summer) year 2006 MODIS 'calibrated radiances' imagery. A 'fuzzy' mask is used to represent mixed land or ice pixels. In this 'floating point' mask (click here to download), values greater than 0.0 and less than 1.0 are assumed to represent 'mixed pixels' of permanent ice, that is, a value of 0.5 is indicative of 50% sub-pixel permanent ice cover. A value of 0.21 represents 21% sub-pixel permanent ice cover. Values of 1.0 represent 'permanent ice cover'. Values of 0.0 represent sea or 'not Greenland', for, the classification is not applied to, e.g., Canadian land area. The image illustrates a fuzzy land classification. Note the gradual color changes in the vicinity of the ice sheet margin. These represent grid cells with a probability between 0% and 100% that permanent ice cover exists.
The data file is binary float with dimensions 1860 x 1740. This page contains other relevant information for reading and re-projecting this grid. This 'mask' is on the same grid as the Greenland Accumulation Grids
[edit] Greenland Ice Sheet Surface Mass Balance Data
The Polar MM5 regional climate model was run over Greenland in a series of 36-hour forecasts spanning 1991–2000 (Box et al. 2004). The model was initialized and constrained by available observations, e.g. satellite-derived temperature and water vapor profiles, sea ice extent, and weather balloon soundings. We analyzed 24-km output over the Greenland ice sheet to evaluate spatial and temporal variability of the surface mass balance and its subcomponents, i.e. precipitation, surface and blowing snow water vapor fluxes, and meltwater production/runoff/retention. The model output was compared with 3 years of independent Greenland Climate Network (GC-Net) automatic weather station (AWS) data from 17 sites, i.e. Steffen et al. (1996); Steffen and Box (2001) and other glacier survey data (e.g. Greuell et al. 2001) to identify model biases. Using the in situ data, we derived simple corrections for biases in melt energy and in water vapor fluxes. The simulated accumulation rate was in agreement with AWS and snow pit observations. Estimates for runoff and the surface mass balance distribution over the ice sheet are produced using modeled meltwater production and the Pfeffer et al. (1991) meltwater retention scheme.
Map of spatial distribution of Greenland ice sheet surface mass balance from Box et al. 2004
Here, we make available annually-resolved grids of accumulation rate, surface mass balance (net accumulation), freshwater discharge (runoff) [ http://polarmet.mps.ohio-state.edu/jbox/data/smb/ following this link]. Data are provided on a 24 km horizontal resolution grid with 55 E-W direction and 101 in the N-S direction, i.e. 55 x 101 grid. Both ASCII and binary data formats are provided. Latitude, longitude, and elevation grids are also provided. More information is available in the README file. We anticipate users of this data can find more errors than we did and we ask only that the data are cited when used in publications. We recommend contacting us for further insight into our model.
Data Citation: Box, J.E., D. H. Bromwich, L-S Bai, 2004: Greenland ice sheet surface mass balance for 1991-2000: application of Polar MM5 mesoscale model and in-situ data, J. Geophys. Res., Vol. 109, No. D16, D16105, 10.1029/2003JD004451. PDF Abstract
Works Cited:
- Box, J.E., D. H. Bromwich, L-S Bai, 2004: Greenland ice sheet surface mass balance for 1991-2000: application of Polar MM5 mesoscale model and in-situ data, J. Geophys. Res., Vol. 109, No. D16, D16105, 10.1029/2003JD004451.
- Greuell W., B. Denby, R.S.W. van de Wal and J. Oerlemans, Ten years of mass-balance measurements along a transect near Kangerlussuaq, Greenland, J. Glaciol., 47(156), 157-158, 2001.
- Pfeffer, W.T., M. F. Meier, and T. H. Illangasekare, 1991: Retention of Greenland runoff by refreezing: Implications for projected future sea-level change, J. Geophys. Res., 96(C12), 22117-22124.
- Steffen, K., J. E. Box, and W. Abdalati, 1996: Greenland Climate Network: GC-Net, US Army Cold Regions Reattach and Engineering (CRREL), CRREL monograph, tribute to M. Meier.
- Steffen, K. and J.E. Box, 2001: Surface climatology of the Greenland ice sheet: Greenland Climate Network 1995-1999, J. Geophys. Res., 106(D24), 33951-33964.
[edit] Greenland Ice Sheet Sublimation/Evaporation Grids
'Sublimation' is here taken to refer to water vapor mass fluxes during melt and sub freezing conditions. Annual sublimation maps are created using a trend surface regression of latitude and elevation and a Greenland DEM .The data are referred to in: Box and Steffen (2001). Seasonal and annual grids of net surface water vapor flux are available following this link. Please also note that polynomial coefficients given in Box and Steffen (2001) can be used to contruct grids for surface sublimation using any DEM, provided also latitude data for the DEM.
Map of spatial distribution of Greenland ice sheet surface water vapor flux in Summer. From Box 2001, PhD Thesis
Citation: