[gradsusr] Lifted Index Formula

[Arlindo da Silva]

On Thu, Mar 1, 2012 at 11:25 AM, Jeff Duda <jeffduda319 at gmail.com> wrote:

> You've confused the different uses of scripting functions vs. Grads prompt
> functions.  You can only display a variable that you have defined using the
> 'define ...' command (note the use of the quotes signaling that it was
> defined as if you typed it in at the Grads prompt).  Your use of variable =
> satvap(...) with satvap being a script function only is causing Grads to
> assume variable is a script variable only, not one that can be displayed.
> The reason you get the other error when you put the other line in quotes is
> because math_exp is strictly a script version of the exp function that you
> would use in the Grads command prompt.  Thus, you would want to change that
> line to
>
> 'es = 6.112*exp(17.67*temp/(temp+243.5))'
>
> in order to display es or define any other variables that would depend on
> it.
>
>

This is generally true but if you are using opengrads you can make the
script function satvap() available to the display command, say

ga-> d satvap(t1000)

by putting it in its own file "satvap.gsf" and loading the corresponding
UDXT as described in the gsUDF
documentation<http://opengrads.org/doc/udxt/gsudf/>.
 Actually, you could in principle implemented the lifted index as a gsUDF
function.

     Arlindo




> Jeff Duda
>
>
> On Thu, Mar 1, 2012 at 7:06 AM, Mike Manning <michael at bsch.au.com> wrote:
>
>> Hi everyone,
>>
>> I'm using data from the FNMOC model and am trying to make a function
>> that calculates Lifted Index.  I'm using bits of the code from the
>> plotskew.gs code.  So far I've got the temperature (celsius) and
>> dewpoint (celsius) worked out for each level.  Now I'm calculating the
>> parcel details.. I've pulled some of the functions and have just been
>> testing to make sure I'm on the right track.  If I have this code for
>> example:
>>
>> 'c'
>> 'reinit'
>> 'open gfs.00z.ctl'
>> 'set t 7'
>> 'set lon 135 155'
>> 'set lat -31 -10'
>>
>> 'set lev 1000'
>> 't1000mb = TMPprs-273.14'
>> 'define dp1000mb =
>>
>> t1000mb-((14.55+0.114*t1000mb)*(1-0.01*RHprs)+pow((2.5+0.007*t1000mb)*(1-0.01*RHprs),3)+(15.9+0.117*t1000mb)*pow((1-0.01*RHprs),14))'
>>
>> variable = satvap2(t1000mb)
>>
>> 'd variable'
>>
>> function satvap2(temp)
>>
>> *---------------------------------------------------------------
>> * Given temp in Celsius, returns saturation vapor pressure in mb
>> *---------------------------------------------------------------
>>
>> es=6.112*math_exp(17.67*temp/(temp+243.5))
>>
>> return(es)
>> 'quit'
>>
>>
>>
>> it complains about an error? If I put the code in the satvap2 function
>> in single quotes it then says "math_exp" is not a variable or function"?
>> I'm a little lost on how to fix this one up if it's possible.
>>
>> Cheers, Mike
>> _______________________________________________
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>> gradsusr at gradsusr.org
>> http://gradsusr.org/mailman/listinfo/gradsusr
>>
>
>
>
> --
> Jeff Duda
> Graduate research assistant
> University of Oklahoma School of Meteorology
> Center for Analysis and Prediction of Storms
>
>
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>
>


-- 
Arlindo da Silva
dasilva at alum.mit.edu
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