# [gradsusr] How to calculate integrated water Vapor transport

kalyan chakravarthy kalyan4space at gmail.com
Thu Nov 14 00:28:41 EST 2019

```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
> _______________________________________________
> gradsusr mailing list
> gradsusr at gradsusr.org
> http://gradsusr.org/mailman/listinfo/gradsusr
>
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