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.
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