Gabriel,

There are several answers to your question:

First, only the CROPGRO model has hourly time-steps (for photosynthesis and growth sensitivities).  So only that model would work the way you want.  All the other DSSAT models operate with ONLY a daily step (daily solar radiation, Tmax, Tmin, rainfall is as far as you can go).  So, no point in doing it for those models.

Second, CROPGRO already does do fraction diffuse and direct beam computation in the hourly leaf to canopy photosynthesis (but with a repeating diurnal pattern).

Lastly, you would need to do significant "input modification" to the CROPGRO model code to feed it with the hourly weather.  This could be done, but it is not trivial unless you are a good programmer.

On the other hand, if you don't have direct beam and diffuse measured directly and separately as part of your input weather data, then I don't see how you can be much better than what we already do.  The important thing is to feed it hourly solar radiation and the current model will already compute the direct and diffuse.  BUT, you could get into the code and change the current algorithm by which we compute direct and diffuse (we use a version of the Spitters Dutch modeling approach).

I hope that helps.

Ken Boote

-----Original Message-----
From: DSSAT - Crop Models and Applications [mailto:[log in to unmask]] On Behalf Of Gabriel Maltais-Landry
Sent: Wednesday, February 02, 2011 4:58 PM
To: [log in to unmask]
Subject: Inputing weather files manually

Hi,

I am a graduate student working on several projects using DSSAT and was wondering if (and how) hourly weather variables computed outside of DSSAT could be inputed to the model. I would like to use different equations to compute the fraction between direct and diffuse sunlight and input this data into DSSAT instead of the default computations of the model. Any hint/suggestion will be greatly appreciated.

Best regards,
Gabriel Maltais-Landry