Subash,
If your data needs are from 1984 to the present, your best alternative source of solar data may be NASA/POWER:
[log in to unmask]" target="_blank">http:[log in to unmask]
Although these data are modeled on a 1 degree lat/long grid, our tests show that the data are often much better than station data. Please see our paper in Agronomy Journal:
https://www.agronomy.org/publications/aj/abstracts/103/4/1242
Best regards,
Jeff White

-----Original Message-----
From: DSSAT - Crop Models and Applications [mailto:[log in to unmask]] On Behalf Of Dr. Subash
Sent: Thursday, December 15, 2011 7:05 AM
To: [log in to unmask]
Subject: Error in estimation of solar radiation from sunshine hours

Dear All,

I am using DSSATv4.5 for simulating the wheat yield over different sites in Northern India.  Here during the months of December and January, there will be no sunshine (Sunshine hours= 0) hours.  But while estimating the solar radiation from sunshine hours during no sunshine hours days will be minimum of 5.4 to 6.0 based on the solar angle and latitude (and the constants a and b).   The actual radiation will be more than this.  This means we are using low solar radiation values and most of the simulations, the biomass production will be far below the actual.  But the grain yield will be comparable. 

My point is whether any other methodology to estimate solar radiation under these circumstances. ie from temperature. Please suggest.

Thanks to all.

With regards
Subash