[gradsusr] Moisture flux convergence/divergence

[Arlindo da Silva]

2011/9/16 Hyacinth Nnamchi <hyacinth.1 at hotmail.com>

>  Jeff,
>
> I seems my question wasn't well framed, and so you dealt with the typo. I
> have attached two Figs showing what the calculations below will give and
> what exactly I'll like to do.
>
>
>From the attached plot it appears that you want to plot the divergent
component of the mass flux, as given by the Helmholtz decomposition:

           http://en.wikipedia.org/wiki/Helmholtz_decomposition

The first step is to compute the velocity potential

   ga-> chi = fish_chi(zon,mer)

(As Roger mentions, make sure to average in the vertical first if this is
what you want.) Next, the divergent component of the mass flux is related to
the gradient of chi; see this for more information:

 Calculating the Divergent
Wind<http://opengrads.org/doc/udxt/fish/fish.html#calculating_the_divergent_wind>

Notice that you will need an opengrads build in order to use the fish
extension; more info here:

    http://opengrads.org/wiki/index.php?title=Installing_the_OpenGrADS_Bundle

 Good luck,

   Arlindo






> Thanks,
>
> Hyacinth
>
>
> > Date: Thu, 15 Sep 2011 17:34:50 -0500>
> From: Jeffrey Duda <jdduda at iastate.edu>>
>  Subject: Re: [gradsusr] Moisture flux convergence/divergence
> > To: GrADS Users Forum <gradsusr at gradsusr.org>
> > Message-ID:
> > <CAP9LQ-VNkxcu-+ey_QkZU7f4MHf+VwJDvav=Dci3ns+x+pjG8Q at mail.gmail.com>
> > Content-Type: text/plain; charset="iso-8859-1"
>
> >
> > Set the graphics output to vector ('set gxout vector'), then 'd zon;mer'
> > (note the semicolon instead of a comma).
> >
> > Jeff Duda
> >
> > 2011/9/15 Hyacinth Nnamchi <hyacinth.1 at hotmail.com>
> >
> > > Hello,
> > >
> > > This is not directly about GrADS but since most of address similar!
> > > problems, I guess someone on this forum will be able to answer my
> question.
> > >
> > > I understand that to calculate moisture transport, given zonal,
> meridional
> > > winds and specific humidity, can simply do:
> > >
> > > 'define zon=uwnd.1*shum.3'
> > > 'define mer=vwnd.2*shum.3'
> > > 'd zon,mer'
> > >
> > > But, I want to plot vectors indicating field of net moisture flux (all
> arrows converging/diverging) instead of just transport.
> > >
> > > Thanks for any ideas.
> > >
> > > Hyacinth
> > >
> > >
> > > __
>
> _______________________________________________
> gradsusr mailing list
> gradsusr at gradsusr.org
> http://gradsusr.org/mailman/listinfo/gradsusr
>
>


-- 
Arlindo da Silva
dasilva at alum.mit.edu
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://gradsusr.org/pipermail/gradsusr/attachments/20110917/f06c2109/attachment-0003.html