How do I create an annual composite of monthly data?

This operation can be done with a few ingrid commands in expert mode and they can be seen at the following link:

Let's go through this a bit of detail.

SOURCES .UMD .Carton .goa .beta7 .u
Selects the zonal wind variable of the UMD Carton dataset.
   T (1980) VALUES
 T (1970) VALUES
 T 120 shiftGRID
 T (1960) VALUES
 T 240 shiftGRID
 T (1950) VALUES
 T 360 shiftGRID
Each of the sections of text separated by a: :a selects the months from the indicated years and adds them together. The a: :a: :a: :a: :a construction allows you to select different time periods. The shiftGRID commands (e.g., T 120 shiftGRID) artificially shift the time grid to match among the different selections of data. For example, 1950 is shifted 30 years forward using "T 360 shiftGRID" so its values can be added to those of 1980.
4 div
This line divides the resulting sum by 4 to find an average for the 4 year composite.

You can now view or download the resulting composite by selecting one of the views links or the Data Files link in the function bar.

-- Michael Bell and Emily Grover