Re: [ferret_users] Volume weighted mean of Ocean Temperature

[Steve Hankin <steven.c.hankin@xxxxxxxx>]

On 2/15/2013 4:10 AM, Star Physicist wrote:

Hi,

I just wanted to know if the following command gives me volume-weighted mean over the 3D ocean volume for temperature field. As you know that the volume of each
  grid-cells is its area, computed from its latitude and longitude range multiplied by its vertical extent, computed from its depth range. So for volume-weighted mean over 3D ocean I am doing as follows:

OceanMaeanTemp=temp[x=@ave,y=@ave,z=@ave,d=1]

The answer is yes.  But a better answer is to suggest that, when you encounter a question like this, think of a way to answer it by  asking Ferret.  For instance, you could define a function that increases linearly in latitude.

    LET myTestFcn = Y[g=temp] + 0*X[[g=temp] + 0*Z[g=temp]

then perform the questionable calculation over an asymmetric range of Y (Y=0:40n or something like that)
    myTestFcn[x=@ave,y=@ave,z=@ave,d=1]

and compare with the unweighted average computed "manually"
    myTestFcn[x=@sum,y=@sum,z=@sum,d=1] / (myTestFcn[x=@ngd]*myTestFcn[z=@ngd]*myTestFcn[z=@ngd])

    - Steve

Thanks,

Mubashar

> Date: Thu, 14 Feb 2013 13:15:20 +0100
> From: hein.zelle@xxxxxxxxxxxxx
> To: couragetoknowgc@xxxxxxxxxxx
> Subject: Re: [ferret_users]
>
> Dear Mubashar,
>
> > Thanks for the idea. Could you please have a look on figure 2 of the following paper regarding volume mean ocean temperature change:
> > http://onlinelibrary.wiley.com/doi/10.1029/2010GL045507/pdf
> >
> > What If for the Z component I compute definite integral or sum as:
>
> I really couldn't tell you - it depends on what you want to calculate!
> I think it's best if you write down the equation you want on paper
> (mathematically), then translate it into ferret code and post to the
> list to ask for help.
>
> At the moment, I have no exact idea what you're trying to calculate, so I
> can't say if the code you write is correct or applicable.
>
> Kind regards,
> Hein Zelle
>
>
> --
>
> Dr. Hein Zelle
> Senior consultant meteorology & oceanography
> BMT ARGOSS
>
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