Regridding with GAMAP

On this page we list some tips and tricks for regridding data with GAMAP. Please also see the following pages:

• General GAMAP usage
• File I/O with GAMAP
• Color and graphics with GAMAP
• Date and time computations with GAMAP
• Text manipulation with GAMAP

--Bob Y. 16:08, 26 November 2008 (EST)

Regridding restart files

GAMAP routines REGRIDH_RESTART and REGRIDV_RESTART may be used to horizontally and vertically regrid restart files from one grid to another. For example, to regrid a restart file from 4° x 5° to 2° x 2.5° resolution use:

REGRIDH_RESTART, INFILENAME='restart.4x5.geos5.2005070100', OUTFILENAME='restart.2x25.geos5.2005070100', OUTRESOLUTION=2

A global restart file can be cut down to a nested-grid domain using the routine CREATE_NESTED.

REGRIDH_RESTART, INFILENAME='restart.4x5.geos5.2005070100', OUTFILENAME='restart.05x0667.geos5.2005070100', OUTRESOLUTION=0.667

CREATE_NESTED, INFILENAME='restart.05x0666.geos5.2005070100', OUTFILENAME='restart.05x0667.NA.geos5.2005070100', /NAMER

Could not read INPSURF error

Several users have reported the following error when regridding bpch files using the GAMAP routine REGRIDH_RESTART:

% CTM_GET_DATA: Invalid diagnostic requested:            0            0            0
% CTM_GET_DATABLOCK: Sorry...no data found!
% REGRIDH_RESTART: Could not read INPSURF!
% Execution halted at: REGRIDH_RESTART   355 /home/mpayer/IDL/gamap2/regridding/regridh_restart.pro

To solve this problem, you will need to modify the diaginfo.dat file in the directory that you are doing the regridding. In that file, change the following line from

10000 PEDGE-$                                  Pressure at level edges                 

to

10000 PS-PTOP                                  Pressure at level edges                 

GAMAP uses the PS-PTOP fields found in IDL/gamap2/data_files for the regridding and is unable to read the fields properly if the diagnostic is not defined in diaginfo.dat.

--Melissa Sulprizio 11:34, 3 September 2013 (EDT)

Regridding T42 to GEOS-Chem grids

Ben Miller wrote:

Justin and I have been working on translating some emission fluxes and deposition velocity data from TOMCAT's T42 grid (128x64, with some variance in latitude step-size) into Geos 4x5 gridboxes. Do you know of any existing routines in IDL or some other language that we could adapt to make the two grids talk to each other?

Philippe Le Sager replied:

There is nothing in IDL to deal with any kind of grid. However (you may have already found it) the RETRO tools (M. Schultz) can regrid data from the T42 to regular grids. It deals with NetCDF files apparently, but ascii/nc conversion is not a problem.

Have a look at the example in the regrid routine of the following package: MGS_Regrid (V2).

--Bob Y. 09:27, 8 August 2008 (EDT)

Regridding from a Lambert conformal grid to a lat-lon grid

Rynda Hudman wrote:

I am trying to plot some North American Regional Reanalysis (NARR) data and compare it to the GEOS precipitation fields. NARR is on a Lambert Conformal grid, so it is irregular and each lat and lon have 2-dimensional arrays defining their 4 corners.

I would like to interpolate/regrid this onto a uniform grid for comparison with GEOS. Could you guys offer some suggestions?

Philippe Le Sager wrote:

You need to look at the "gridding and interpolation" chapter of the IDL guide/help. You can directly go to the MIN_CURVE_SURF function though. This is the one I have mostly used. Works like a wonder.

--Bob Y. 10:32, 6 November 2008 (EST)