Grads allows you use a single data descriptor file to aggregate multiple data files and handle them as if they were one individual file. The individual data files must be identical in all dimensions except time and in a format GrADS can read. The time range of each individual file must be indicated it its filename.
An example might be a timeseries spanning a single month, where each day's worth of hourly data is contained in individual files:
1may92.dat 2may92.dat ... 31may92.dat
In order to tell GrADS that there are multiple files in this time series, three records are modified in the data descriptor (.ctl) file:
DSET %d1%mc%y2.dat
OPTIONS template
TDEF 744 linear 0z1may1992 1hr
First, the DSET entry has a substitution template instead of a
filename. See below for a description of all the possible components
of the template. Second, the OPTIONS entry contains the
template keyword. Third, the TDEF entry describes
the time range for the entire set of data files.
Templating works on the following GrADS data types: gridded binary,
GRIB, and station data. If you specify any additional
options keywords in the data descriptor file, make sure
the options apply equally to each file included in the template.
Valid components of the substitution template are as follows:
%y2 2 digit year %y4 4 digit year %m1 1 or 2 digit month %m2 2 digit month (leading zero if needed) %mc 3 character month abbreviation %d1 1 or 2 digit day %d2 2 digit day (leading zero if needed) %h1 1 or 2 digit hour %h2 2 digit hour %h3 3 digit hour (e.g., 120 or 012) %f2 2 or 3 digit forecast hour %f3 3 digit forecast hour %n2 2 digit minute (leading zero if needed)When specifying the initial time (e.g., NWP model output from NMC and FNMOC), use these substitutions:
%iy2 initial 2 digit year %iy4 initial 4 digit year %im1 initial 1 or 2 digit month %im2 initial 2 digit month (leading zero if needed) %in2 initial 2 minute (leading zero if needed) %imc initial 3 character month abbreviation %id1 initial 1 or 2 digit day (leading zero if needed) %id2 initial 2 digit day %ih1 initial 1 or 2 digit hour %ih2 initial 2 digit hour %ih3 initial 3 digit hour