Re: [ferret_users] Putting a pseudo-variable on the J axis

[Abhisek Chatterjee <chatterjeea.ocean@xxxxxxxxx>]

Hi Ryo,

Thank you for the clarification. I have one more doubt about @DIN over irregular grids.

I mainly deal with netcdf files of model outputs which usually contain bound information for depth. Hence, I frequently use @DIN function over Z axis assuming that Ferret takes care of irregular depth coordinate. 

Please correct me if I am wrong.

Thanks,

Abhisek 

---------------------------
Abhisek Chatterjee, PhD

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On Fri, Aug 4, 2017 at 7:38 AM, Ryo Furue <furue@xxxxxxxxxx> wrote:

Hi all,

As Ryo suggested there are easier way to calculate volume transport through a wall.

I.e. if you want to calculate volume transport across 10N, between 60:90E and 0:300 m, then it may be represented as below:

Vol_tr=v[x=60:90@din,y=10,z=0:300@din]

Thank you. I had something like that in mind.

It really depends on your purpose and the accuracy you pursue, but I just put some random thoughts/caveats here:

- When your grid is non-uniform, @DIN will result in some error, if the axis isn't "properly" set.  List the XBOX, YBOX, or ZBOX variable to check. (If we are dealing with a netCDF file, I'm referring to the "_bnds" information.)

- If your model uses a C-grid, then @DIN is the right thing.  If your model uses a B-grid, you will first need to map the velocity onto the C-grid points, like

let vm = v[gx=C_grid_xaxis@LIN]

- If you really need volume fluxes through each face of each gridbox, they can be calculated as

let vflx = v * xbox[g=v] * zbox[g=v]

   provided that your non-uniform axes are "properly" set.

Hope this helps,

Ryo