Re: [ferret_users] Spatial average on irregular domain

[Ansley Manke <ansley.b.manke@xxxxxxxx>]

Hi-
This is not a simple question, is it.  The size of the grid cells on a 
curvilinear grid may vary from cell to cell, so to compute an accurate 
average you would need to find a way to compute the area of the cells.  
On a rectilinear grid, Ferret computes the actual size of the grid cells 
using a simple latitude correction, but it does not have a means of 
doing that on a curvilinear grid.  Does the dataset have variables that 
describe the area of cells? Some datasets do include that information.  
If so then we could find a way to create a mask using the curvilinear 
coordinate variables, along the lines of

let mask = if curv_lat gt -30 and curv_lat lt 30 then 1

and compute the average of the data multiplied by that mask. Another 
option would be to regrid the data to a rectilinear grid and take the 
average of the regridded field over the region.

Ansley

On 11/3/2011 6:09 AM, markus.mingel@xxxxxxxxx wrote:
> Dear All,
> I am trying to perform a spatial average on irregular domain.
>
> I know how to do that on regular domains:
>
> let regional_ SST = SST[x=-180:180@ave,y=-30:30@ave]
>
> however this command does not work or curvilinear grids. Could you please
> suggest me how to compute spatial averages in such case?
>
> Thanks for help
>
> Regards
> Markus