Dear Dssat Community:

Using data on sunlight duration from a weather station in Thailand, we have
converted sunlight duration hours to solar radiation in MJ/m2/day using the
Weatherman sunlight duration/solar radiation conversion routine (when
importing from the raw data import grid).  However, the resulting estimated
solar radiation values in the Weatherman weather database that is created
appear to be somewhat low:  none of the estimated solar radiation daily
values exceed 20 MJ/m2/day, even during the summer months.

We are wondering if anyone might have an idea why the estimated values seem
somewhat low?  The input sunlight duration hours for a weather station in
Surin Province, Thailand were obtained directly from the Thai
Meteorological Department, and for 1998 range from 0 to 11.4, with a mean
of 6.89 and a stdev of 2.72.  The estimated solar radiation values for the
same days from Weatherman range from 4.6 to 18, with a mean of 12.5 and
stdev of 3.02.  We specified "hours of bright sunshine" as the units in the
Weatherman raw data import grid, and were careful to specify the correct
latitude/longitude of the station as well as its elevation above sea level
in meters.

Thanks for any help or advice.  Is the Weatherman model for converting
sunlight duration to solar radiation reliable?  Are there alternative
methods for converting that anyone may be aware of?

John Felkner
University of Chicago