[gradsusr] How to calculate integrated water Vapor transport

Jeff Duda jeffduda319 at gmail.com
Thu Nov 14 13:48:43 EST 2019


And what about the data themselves? A control file would be helpful here...

On Wed, Nov 13, 2019 at 11:41 PM kalyan chakravarthy <kalyan4space at gmail.com>
wrote:

> Hello Jeff,
>
> I have used the vint() function from Grads. The pressure is in millibars,
> q (sp. humidity) is kg/kg, u is in m/s, v is in m/s.
>
> Please find the attached gs files IVT.gs and vintmoisture.gs
>
> *I have used these functions *
>
> 'define um=q*u'
> 'define vm=q*v'
> 'define ium=vint(1000,um,300)'
> 'define ivm=vint(1000,vm,300)'
> 'set gxout shaded'
> 'd mag(1.e-2*ium,1.e-2*ivm)' (from moisture.gs file)
> 'vimf=-hdivg(ium,ivm)
>
> Thanks for your help.
>
> Regards
>
> *Kalyan Chakravarthy Yesoda*
>
> Graduate Student, PhD
> University of Nevada, Reno
> Mobile no: 775-420-9434
>
>
>
> On Wed, Nov 13, 2019 at 8:16 PM Jeff Duda <jeffduda319 at gmail.com> wrote:
>
>> Are you sure your input fields have the correct (SI) units? Also, i don't
>> know what grads formula you're using to perform the integral, but vint()
>> assumes pressure coordinates in *millibars* rather than Pascals, so that
>> may be a source of your problem.
>>
>> I don't work with IVT, and the formulas I found online don't match what
>> you indicated, so I can't say for sure if the problem is with the
>> formulation or not.
>>
>> Jeff Duda
>>
>> On Wed, Nov 13, 2019 at 8:39 PM kalyan chakravarthy <
>> kalyan4space at gmail.com> wrote:
>>
>>> Hello Everyone,
>>>
>>> I need some help to calculate Integrated Water vapor transport (IVT)
>>> from surface to 300hPa.  I am using ERA-Interim data (uwind (u), vwind(v),
>>> specific humidity(q)). I have used the scripts that are published in the
>>> grads user forum, but the results seems wrong (ex. the values are from
>>> 40000 kg/ms).
>>>
>>> The formula I am using to calculate the IVT is
>>>
>>> IVT=Sqrt((integral(q*u)*dp)^2+((integral(q*v)*dp)^2)
>>>
>>> Integration is from Surface to 300 hPa.
>>>
>>>
>>> Thanks
>>>
>>> Kalyan
>>>
>>>
>>> --
>>> *Kalyan Chakravarthy Yesoda*
>>>
>>> Graduate Student, PhD
>>> University of Nevada, Reno
>>> Mobile no: 775-420-9434
>>>
>>>
>>> _______________________________________________
>>> gradsusr mailing list
>>> gradsusr at gradsusr.org
>>> http://gradsusr.org/mailman/listinfo/gradsusr
>>>
>>
>>
>> --
>> Jeff Duda, Research Scientist
>> University of Colorado Boulder
>> Cooperative Institute for Research in Environmental Sciences
>> NOAA/OAR/ESRL/Global Systems Division
>> Boulder, CO
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>> gradsusr mailing list
>> gradsusr at gradsusr.org
>> http://gradsusr.org/mailman/listinfo/gradsusr
>>
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-- 
Jeff Duda, Research Scientist
University of Colorado Boulder
Cooperative Institute for Research in Environmental Sciences
NOAA/OAR/ESRL/Global Systems Division
Boulder, CO
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