Dear clooegue, Sorry, not to answer you at the moment. However,I will read some literature and may be able to explain. Regards. Aslam Gill >From: James Hansen <[log in to unmask]> >Reply-To: DSSAT - Crop Models and Applications <[log in to unmask]> >To: [log in to unmask] >Subject: Re: WEATHER GENERATOR >Date: Wed, 14 Mar 2001 16:46:31 -0500 > >Dear Anamika, > >Netscape 6 is preventing me from opening your more recent message. >Detail about the problem from that message would have been useful to >DSSAT LISTSERV recipiants. > >In the data set that you sent me, there seems to have been only one >March rainfall observation through the period of record. I did not >implement the gamma distribution parameter estimation algorithm, and do >not understand it completely. However, you can see the potential (and >so far quite rare) problem of fitting a 2-parameter rainfall >distribution to one observation. The resulting negative alpha parameter >value was incorrect. I added a simple fix that sets alpha = 0.988 >(i.e., just below the upper limit of one). WM will calculate beta based >on alpha and the mean wet-day amount (i.e., alpha * beta = rwet), giving >you a distribution with the correct mean but an arbitrary shape and >variance. Since many DSSAT LISTSERV users may not be able to handle >large attachments, I will send the modified version (both the DSSAT and >Y2K-compliant versions) directly to you. > > >anamika arora wrote: > >>Does anyone know that while generating ".cli" files from observed weather >>why the value of alpha comes out to be zero for some months, >>even when the data format is correct. >>_________________________________________________________________________ >>Get Your Private, Free E-mail from MSN Hotmail at http://www.hotmail.com. > > >-- >Dr. James W. Hansen >Associate Research Scientist - Agricultural Systems >International Research Institute for Climate Prediction >P.O. Box 1000 >Palisades, NY 10964-8000 >USA > >845-680-4410 (voice) >845-680-4864 (fax) _________________________________________________________________________ Get Your Private, Free E-mail from MSN Hotmail at http://www.hotmail.com.