Greenland Accumulation Grids
From Byrd Polar Research Center - Research Wiki
Greenland Ice Sheet Snow Accumulation Grids
This project was to derive a new more accurate Greenland ice sheet accumulation map, and also having annual resolution for 51 years (1958-2008). Earlier climatologies lacked tie points in the high accumulation orographic region and missed 70 Gt of mass by interpolating across the peaks in terrain-induced snowfall maxima. This project maximized the respective accuracy of ice core and undercatch-corrected precipitation gauge point measurements with the spatial patterns of orographic precipitation captured by the Polar MM5 regional climate data assimilation model. J. Box provided in-situ ice core data from the PARCA program via Ellen Mosely-Thompson at Byrd Polar Research Center and Joe McConnell at Desert Research Institute. J. Box provided the Polar MM5 regional climate data assimilation model output from a collaborative project with David Bromwich at Byrd Polar Research Center. Evan Burgess at University of Utah compensated spatial biases in simulated snow accumulation for his Master’s thesis with supervision and statistical insight from Richard Forster (University of Utah Geography Department).
Burgess, E. W., R. R. Forster, J. E. Box, E. Mosley‐Thompson, D. H. Bromwich, R. C. Bales, and L. C. Smith (2010), A spatially calibrated model of annual accumulation rate on the Greenland Ice Sheet (1958–2007), J. Geophys. Res., 115, F02004, doi:10.1029/2009JF001293. PDF
Summary of results
Past estimates of Greenland Ice Sheet accumulation rates have been multi-year climatologies based on ice/firn cores and coastal precipitation records. Existing annually resolved estimates have incompletely quantified uncertainty, due primarily to incomplete spatial coverage. This study improves upon these shortcomings by calibrating annual (1958-2007) solid precipitation output from the Fifth Generation Mesoscale Model modified for polar climates (Polar MM5) using firn core and meteorological station data. The calibration employs spatial interpolation of regionally derived linear correction functions. Residual uncertainties exhibit coherent spatial patterns, which are modeled via spatial interpolation of root mean squared errors. Mean 1958-2007 Greenland Ice Sheet annual accumulation rate is 337±48 mm w. eq. or 591±83 Gt. Annual estimates contain one standard deviation uncertainties of 74 mm w. eq., 22%, or 129 Gt. Accumulation rates in southeast Greenland are found to exceed 2000 mm w. eq. and to dominate inter-annual variability in Greenland Ice Sheet total accumulated mass, representing 31% of the whole. Higher accumulation rates in the southeast are of sufficient magnitude to affect the sign of Greenland mass balance during some years. The only statistically significant temporal change in total ice sheet accumulation in the 1958-2007 period occurred between 1960 and 1972 when a simultaneous accumulation increase and decrease occurred in west and east Greenland, respectively. No statistically significant uniform change in ice-sheet-wide accumulation is evident after 1972. However, regional changes do occur, including an accumulation increase on the west coast post-1992. The high accumulation rates of 2002-2003 appear to be confined to the southeast.
NEW: Hydrologic Year Data are available for download here
We would appreciate a brief response by email if you use this data set. We've already had to contact known users to alert of an important and now corrected issue with the data.
Grids are provided following this link at 1.25 km resolution. Grid dimensions are 1860x1760. The data are provided as annual (calendar year) files. The data type on all grids is binary floating point. Latitude and longitude data on the same grid are provided. The upper left grid center is at lat,lon = 67.710165 -82.661613. The lower-right grid center is at lat,lon = 67.400613 -2.589502.
Re-projecting the data? The projection information in the files GL1250.gpd and N200correct.mpp, see below and/or in the download directory. One can use the NSIDC mapx or regrid tools to change the projection. regrid is part of the MS2GT package available from The National Snow and Ice Data Center (NSIDC). The MapX library is also from NSIDC available from here.
NEW (2009 09 Oct) gtest is an executable useful in identifying the corner points. Below, we get the corner coordinates (lat, lon) for the grid...
enter col row: 0 0
lat,lon = 67.705201 -82.677930 (upper left corner)
enter col row: 1859 1739
lat,lon = 67.406094 -2.604522 (lower right corner)
enter col row: 0 1739
lat,lon = 58.197311 -44.418189 (lower left corner)
enter col row: 1859 0
lat,lon = 86.997536 -19.863645 (upper right corner)
see this MS2GT tutorial for further information. Thanks Terry Haran andd Ken Knowles of NSIDC!
The following concepts are useful in re-projecting data. Points, Pixels, Grids, and Cells: A Mapping and Gridding Primer. For further information about the contents of these files consult the documentation for the MapX library.
Example: Using MapX to convert the PMM5 data to NSIDC 25x25 km sea ice grid using nearest neighborhood interpolation. resamp -f -c N Gl1250.gpd N3B.gpd [input data] [output data]
Load the data in IDL
Below is an example of IDL code to read the data...
openr,1,fname readu,1,data close,1
More complete IDL code is in the download directory. See the .pro files (open_snowacc.pro open_ancdata.pr0, plot_map.pro)
map projection parameters:
N200correct.mpp map projection parameters...
90.0 0.0 lat0 lon0
200.5402 scale (km/pixel)
90.00 00.00 center lat lon
0.00 90.00 lat min max
-180.00 180.00 lon min max
15.00 30.00 grid
0.00 00.00 label lat lon
1 0 0 cil bdy riv
N200correct.mpp map projection parameters # EASE-Grid
1860 1740 columns rows # Greenland
160 grid cells per map unit # 1.25 km
1949.5 -250.5 map origin column,row
Arc GIS Projection Instructions A binary grid can be imported into ArcGIS using the ArcToolbox tool “Float to Raster.” The binary grid must be accompanied by a header file (.hdr) file of the same name. Formatting of header files has changed between ArcGIS vers. 9.2 and 9.3. See documentation for appropriate format. The data is provided as band sequential (bsq) and byte-order type “I”. The lower left corner or upper left corner must be provided in EASE-Grid coordinates, not lat/lon (see values below).
Example .hdr file for one year grid (xyz dimensions of 1860,1740,1) for ArcGIS 9.2:
NCOLS 1860 NROWS 1740 XLLCORNER -2443456.992 YLLCORNER -2493592.067 CELLSIZE 1250 BYTEORDER LSBFIRST
Once grid is imported, define the projection with the “Define Projection” tool in ArcToolbox. Select grid then click coordinate system button. Select “Create new coordinate system—projected.” In the next window, name the coordinate system, select “Lambert_Azimuthal_Equal_Area”
Enter the following: False_Easting 0.000000000000000000 False_Northing 0.000000000000000000 Central_Meridian 0.000000000000000000 Latitude_Of_Origin 90.000000000000000000
Linear Unit: meter
Create a new geographic coordinate system, name it. Specify semimajor and semiminor axes of 6371228. Angular unit of “degrees.” Prime meridian of “Grenwich.” Finish.
Now that the grid has been established re-project the grid using the “Project Raster” tool in Arctoolbox as with any other gridded data.
This page was compiled by J. Box, Byrd Polar Research Center
National Science Foundation support
This work has been supported by National Science Foundation Office of Polar Programs Award ARC-090946 and ARC-0909499 managed by H. Edmonds.