Re: [ferret_users] Conservative remapping

[Lev Tarasov <lev@xxxxxx>]

Markus;
      ferret's an awkward tool for conservative remapping. It would
entail  just a few lines of commands with CDO
https://code.zmaw.de/projects/cdo
(or maybe also with NCO, choice depends on who you have around that's 
familiar with either tool)

Lev Tarasov -   Dept of Physics and Physical Oceanography,
		Memorial University of Newfoundland.
                email: lev@xxxxxx
                http://www.physics.mun.ca/~lev/
		Tel (709)-864-2675
		Fax (709)-864-8739

On Tue, 22 May 2012, markus.mingel@xxxxxxxxx wrote:

> Dear All,
>
> I would regrid a variable defined in gC/m2 on a regular grid to a new regular
> grid; since the variable is a flux, I should use a mass conservation. Iin order
> to have a variable independent by the cell area I tried to multiply the
> variable by the area before the regridding, and then I divided by the new area
> after the regridding, however when I check the global value on the new grid
> this is not the expected value.
> Here a sample code:
>
> USE npp.nc
>
> DEFINE AXIS/X=-179.5:179.5:1 xaxis
> DEFINE AXIS/Y=-89.5:89.5:1   yaxis
> DEFINE GRID/X=xaxis/Y=yaxis  reg_grid
>
> let dummy = y[gy=yaxis] + x[gx=xaxis]
>
> ! Computing the area of the new grid
>
> LET r=6370*1000		! radius of earth in m
> LET pi=atan(1.)*4.
> LET deg2rad=pi/180.
> LET deg2km=1000*2*pi*r/360.
>
> LET Final_area=xbox[g=dummy]*ybox[g=dummy]*cos(y[g=dummy]*deg2rad)
> *deg2km*deg2km*1e-6
> LET Original_area=xbox[g=npp]*ybox[g=npp]*cos(y[g=npp]*deg2rad)
> *deg2km*deg2km*1e-6
>
> let npp_partial  = npp * Original_area
> let npp_new     = npp[G=reg_grid]
> let npp_final     = npp_new /  Final_area
>
> The global value of npp is 106 Pg, while  npp_final has a much lower value.
> Any suggestions?
>
> Best
> Markus

This electronic communication is governed by the terms and conditions at
http://www.mun.ca/cc/policies/electronic_communications_disclaimer_2012.php