Report 58:  An Objective Method for Generating Land/Sea Masks for use in GCM Simulations

Taylor, Karl E. and Charles Doutriaux

August 2000, 20 pp. 

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Most general circulation models (GCM's) require prescription of certain surface conditions, in particular a land/sea mask indicating whether grid cells are underlain by soil and vegetation or by water. Here we describe an algorithm that produces highly realistic land/sea masks at any desired resolution. Based on a high-resolution (1/6-degree longitude/latitude) data set that provides the fraction land in each grid cell, we determine, as a first approximation, whether the land fraction in each grid cell of the model exceeds 50%. Those grid cells meeting this criterion are tentatively designated land. We then adjust this first approximation to obtain a more accurate representation of islands and lakes that are about the same size of a single model grid cell but that straddle two or more model grid cells. Under the first approximation, these small islands and lakes tend to be omitted, but under an iterative scheme, they are included, though slightly displaced in position. This scheme also tends to better represent locally the relative fraction of land and ocean along coastlines.(pdf file)
 

UCRL-MI-123395