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Files grl{04,05,08,10,16,20,40}_zwally2012_basins(_with-negis)
                                                  _extrapolated.nc
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Zwally+2012 basins extrapolated to the entire computational domain.
Horizontal resolutions 04/05/08/10/16/20/40 km.
The '_with-negis' versions contain an additional region for the
North-East Greenland Ice Stream (NEGIS), defined by a threshold
surface velocity of 50 m/a.
Processing by Ralf Greve.

Reference
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Zwally, H. J., M. B. Giovinetto, M. A. Beckley and J. L. Saba. 2012.
Antarctic and Greenland drainage systems.
GSFC Cryospheric Sciences Laboratory, Greenbelt, MD, USA,
http://icesat4.gsfc.nasa.gov/cryo_data/ant_grn_drainage_systems.php
