[gradsusr] what is the unit of moisture convergence?

Mohsen Soltani soltani.clima at gmail.com
Tue Jun 11 01:58:04 EDT 2013 

Hi Kishore,

Use the following script to calculate moisture convergence:
***********************************************************************
************************************************
* rh    = Relative Humidity in %
* t     = Temp at *set level in degrees Kelvin
* tc    = Temp in degrees C
 * td    = Dewpoint at *set level in degrees C
* e     = Vapor pressure
* mixr  = Mixing ratio
* u     = U-wind in m/s
* v     = V-wind in m/s
* mconv = moisture convergence/divergence.

'tc = (t-273.16)'
'td = tc-((14.55+0.114*tc)*(1-0.01*rh) + pow((2.5+0.007*tc)*(1-0.01*rh),3)
+ (15.9+0.117*tc)*pow((1-0.01*rh),14))'
'vapr = 6.112*exp((17.67*td)/(td+243.5))'
'e = vapr*1.001+(lev-100)/900*0.0034'
'mixr = 0.62197*(e/(lev-e))*1000'
'mconv = (1)*hdivg(u*mixr,v*mixr)*1e4'
'd mconv'
****************************
**************************************************
I have to say that neither vapor pressure, mixing ratio nor even dewpoint
temperature is needed! This is because, equation (2) computes dewpoint
temperature:
That is:
'td =
tc-((14.55+0.114*tc)*(1-0.01*rh)+pow((2.5+0.007*tc)*(1-0.01*rh),3)+(15.9+0.117*tc)*pow((1-0.01*rh),14))'

**************************
Therefore, you only need 4 variables to calculate moisture convergence:
Those are:

1- relative humidity (%)
2- air temperature (K)
3- u-wind component (m/s)
4-v-wind component (m/s)
*************************************************
All you have to do is to define variables based on the equations in the
script. For example:

define u = uwnd
define v = vwnd
define t = air
define rh = rhum
**********************************************************
I'm attaching a "moisture convergence plot" over Iran. Based on the plot,
the convergence (positive) areas shown in green color and vice versa. To
verify my output, I overlaid wind streams. They are quite in a good
agreement with convergence and divergence regions.

BTW, that's a surface level. And as Davide suggested, the unit of the MC
will be: (g/kg*s-1)


Good luck,
Mohsen


--
some are weather-wise some are otherwise!
--
Best Wishes,
(Mr.) Mohsen Soltani
Climatology Grad Student (M.Sc.),
Faculty of Geography, University of Tehran, Tehran, Iran
Tel: (+98) 9119772934
e-mail: soltani.clima at gmail.com


On Mon, Jun 10, 2013 at 9:59 PM, Kishore Ragi <kishoreragi at gmail.com> wrote:

> Dear users,
>
> I can understand how to calculate moisture convergence with specific
> humidity/mixing ratio but, I have relative humidity.
>
> Could anybody please help me how to calculate moisture convergence with
> relative humidity?
>
> Thank you in advance,
>
> Sincerely,
>
> Kishore
>
>
> On Thu, May 30, 2013 at 7:11 PM, Mohsen Soltani <soltani.clima at gmail.com>wrote:
>
>> Dear Davide,
>>
>> It sounds logical! Thank you very much for your kindness.
>>
>> Mohsen
>>
>> --
>> some are weather-wise some are otherwise!
>> --
>> Best Wishes,
>> (Mr.) Mohsen Soltani
>> Climatology Grad Student (M.Sc.),
>> Faculty of Geography, University of Tehran, Tehran, Iran
>> Tel: (+98) 9119772934
>> e-mail: soltani.clima at gmail.com
>>
>>
>> On Thu, May 30, 2013 at 2:54 AM, Davide Sacchetti <
>> davide.sacchetti at arpal.gov.it> wrote:
>>
>>> specific humidity is defined as ratio of water vapor mass (g) over air
>>> mass (kg) (units: g/kg)
>>> mixing ratio is almost the same: ratio of water vapor mass (g) over DRY
>>> air mass (kg) (units: g/kg)
>>>
>>> your divergence is like d(u*mixr)/dx, then has units of (m/s * g/kg)/m:
>>> units should be g/kg*s-1
>>>
>>> bye bye
>>> Davide
>>>
>>> On Thu, 2013-05-30 at 01:39 -0700, Mohsen Soltani wrote:
>>> > Dear GrADS Users,
>>> >
>>> >
>>> > I employed the following script to display the moisture convergence.
>>> > But, I don't know what is the unit of the output! Please see the
>>> > attached plot and let me know what's your opinion.
>>> >
>>> >
>>> >
>>> ************************************************************************
>>> > * rh    = Relative Humidity in %
>>> > * t     = Temp at *set level in degrees Kelvin
>>> > * tc    = Temp in degrees C
>>> > * td    = Dewpoint at *set level in degrees C
>>> > * e     = Vapor pressure
>>> > * mixr  = Mixing ratio
>>> > * u     = U-wind in m/s
>>> > * v     = V-wind in m/s
>>> > * mconv = moisture convergence/divergence.
>>> >
>>> >
>>> > 'tc = (t-273.16)'
>>> > 'td = tc-((14.55+0.114*tc)*(1-0.01*rh) + pow((2.5
>>> > +0.007*tc)*(1-0.01*rh),3) + (15.9+0.117*tc)*pow((1-0.01*rh),14))'
>>> > 'vapr = 6.112*exp((17.67*td)/(td+243.5))'
>>> > 'e = vapr*1.001+(lev-100)/900*0.0034'
>>> > 'mixr = 0.62197*(e/(lev-e))*1000'
>>> > 'mconv = (1)*hdivg(u*mixr,v*mixr)*1e4'
>>> > 'd mconv'
>>> > ********************************************************
>>> >
>>> >
>>> >
>>> >
>>> > Thank you,
>>> > Mohsen
>>> >
>>> >
>>> > --
>>> > some are weather-wise some are otherwise!
>>> > --
>>> > Best Wishes,
>>> > (Mr.) Mohsen Soltani
>>> > Climatology Grad Student (M.Sc.),
>>> > Faculty of Geography, University of Tehran, Tehran, Iran
>>> > Tel: (+98) 9119772934
>>> > e-mail: soltani.clima at gmail.com
>>> >
>>> > _______________________________________________
>>> > gradsusr mailing list
>>> > gradsusr at gradsusr.org
>>> > http://gradsusr.org/mailman/listinfo/gradsusr
>>>
>>> --
>>> --> Attenzione cambio indirizzo: davide.sacchetti at arpal.gov.it
>>> --
>>> Davide Sacchetti
>>> Centro Funzionale Meteo Idrologico di Protezione Civile della Regione
>>> Liguria
>>> ARPAL Unità Tecnica Complessa di livello Regionale
>>> V.le Brigare Partigiane 2 16121 Genova (I)
>>> tel: +39 010 6437535                    fax: +39 010 6437520
>>> mail: davide.sacchetti at arpal.gov.it     web: www.meteoliguria.it
>>>
>>>
>>> _______________________________________________
>>> gradsusr mailing list
>>> gradsusr at gradsusr.org
>>> http://gradsusr.org/mailman/listinfo/gradsusr
>>>
>>
>>
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