Re: Regridding/interpolation

[Mark Verschell <verschell@xxxxxxxxxxxxxxxxxxxxx>]

Glenn,

	I haven't worked this out in any way, but it occurs to me that you
could do something very similar to how ferret handles sigma-coordinate
date.

	In sigma coordinate data, you have data in levels, and you have
the thickness of each level. You define a depth function that is the sum
of these thicknesses and then I define a new axis that has the resolution
I want and regrid using zaxreplace. So maybe something like:

let depth=h[k=@rsum]-0.5*h
define axis/z=0:200:10/depth/unit=meters zdepth
let varD=ZAXREPLACE(var,depth,z[gz=zdepth]

Could be adapted, where depth would be replaced by pressure. You already
have a pressure variable, so if you define a "regular" pressure z-axis:

define axis/z=0:1000:10/depth/unit=decibars zpres
let trd=ZAXREPLACE(tr,pressure,z[gz=zpres])

Give it a try, this method is likely to require modification for your
case.

	Mark


On Tue, 20 Jun 2000, Glenn Carver wrote:

> I have a variables, say tr,  on a regular lat/long/theta grid (theta is
> potential temperature). I also have pressure, p, on this same grid. I need
> to regrid the variables onto a new grid which has the vertical coordinate
> replaced by pressure. To be able to do this requires a linear vertical
> interpolation using the values of pressure in p. However, since p for each
> lat/lon is different I cannot figure out a way of getting ferret to do this.
> 
> e.g.
> define/axis/z=500:0:-10 paxis   ! defines the regular pressure axis I want
> define grid/like=tr/z=paxis newgrid  ! sets up the grid I eventually want tr on
> 
> I can't use the normal regridding as this uses the variable's underlying
> grid whereas I need a lookup to the pressure variable to find the z
> coordinate value. I can't use an objective analysis ext. fn. because that's
> going to do a 2D interpolation and I only need a 1d (vertical in this case)
> interpolation.
> 
>   Thanks,
> 
>           Glenn
> 
> 
> --
> Dr. Glenn Carver, Senior Research Associate,
> Centre for Atmospheric Science, Chemistry Dept., Cambridge University, UK
> mailto:Glenn.Carver@atm.ch.cam.ac.uk   http://www.atm.ch.cam.ac.uk/~glenn/
> 
>               "I never think of the future, it comes soon enough"
>                    - Albert Einstein
> 
>