Files in this directory are Reanalysis fields of
geopotential height of the earth's surface and
land/sea masks.  GrADS control and index files
are included for each GRIB data file.  The
height fields are derived from spectral representation
and will have oscillations over the ocean with some
negative values.

Gaussian grid land/sea mask.
gau_mask.grb
gau_mask.grb.ctl
gau_mask.grb.idx

Gaussian grid geopotential height.
hgtgau90.sfc
hgtgau90.sfc.ctl
hgtgau90.sfc.idx

Lat-lon grid land/sea mask.
mask.grb
mask.grb.ctl
mask.grb.idx

Lat-lon grid geometric height
orog.grb
orog.grb.ctl
orog.grb.idx

Is the field called geopotential height of the earth's surface always the
same throughout the entire Reanalysis period?[5/5/2000]

The geopotential height of the earth's surface that is stored in the grbsanl file
on the Gaussian grid is derived from the spectral sigma file and the code that
does this derivation has changed three times. There was a change on 21
September 1994 and a change on 27 January 1998 which have no effect on
the values. A change made on 22 January 1998 did cause some differences
and fields before this date will be different from fields after this date.
Otherwise this field is the same throughout the period. This change only
affects this particular field and only in the grbsanl file. The same field on the
.5x2.5 lat-lon grid is not affected and is the same throughout the period.