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.
>>_________________________________________________________________________
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>
>
>--
>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)

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