Re: [gembud] Interpolating levels in GRIB data

Hi Mark,

You could do the following:


Using GDINFO output, identify the GFUNC, GLEVEL, GVCORD of interest.  For
example, using today's 0Z GFS grid I do the following:

GDFILE = gfs_3_20091116_0000_006.grd
 LSTALL  = YES
 OUTPUT  = T
 GDATTIM = all
 GLEVEL  = all
 GVCORD  = all
 GFUNC   = all
 GEMPAK-GDINFO>r

I'm interested in RELH at 800, 700, 600, and 500 mb in New York City, NYC
(40.783, -73.883).  Within the GDINFO output I see:

  100     091116/0000F006                        800         PRES RELH
  116     091116/0000F006                        700         PRES RELH
  132     091116/0000F006                        600         PRES RELH
  148     091116/0000F006                        500         PRES RELH

Using GDPOINT, pull the RELH values of interest:

gdpoint
GDATTIM  = 091116/0000F006
 GDFILE   = gfs_3_20091116_0000_006.grd
 GLEVEL   = 800
 GPOINT   = 40.783;-73.883
 GVCORD   = PRES
 GFUNC    = RELH
 SCALE    = 0 
GEMPAK-GDPOINT>r

GDFILE: gfs_3_20091116_0000_006.grd
GPOINT: 40.783;-73.883
GVCORD: PRES
GLEVEL: 800
GFUNC : RELH
SCALE : 0
     091116/0000F006 :     58.81023
 Parameters requested: GDATTIM,GDFILE,GLEVEL,GPOINT,GVCORD,GFUNC,SCALE.
 GEMPAK-GDPOINT>GLEVEL=700
 GEMPAK-GDPOINT>r

GDFILE: gfs_3_20091116_0000_006.grd
GPOINT: 40.783;-73.883
GVCORD: PRES
GLEVEL: 700
GFUNC : RELH
SCALE : 0
     091116/0000F006 :     27.16799
 Parameters requested: GDATTIM,GDFILE,GLEVEL,GPOINT,GVCORD,GFUNC,SCALE.
 GEMPAK-GDPOINT>GLEVEL=600
 GEMPAK-GDPOINT>r

GDFILE: gfs_3_20091116_0000_006.grd
GPOINT: 40.783;-73.883
GVCORD: PRES
GLEVEL: 600
GFUNC : RELH
SCALE : 0
     091116/0000F006 :      8.15741
 Parameters requested: GDATTIM,GDFILE,GLEVEL,GPOINT,GVCORD,GFUNC,SCALE.
 GEMPAK-GDPOINT>GLEVEL=500
 GEMPAK-GDPOINT>r

GDFILE: gfs_3_20091116_0000_006.grd
GPOINT: 40.783;-73.883
GVCORD: PRES
GLEVEL: 500
GFUNC : RELH
SCALE : 0
     091116/0000F006 :      3.61722
 

GDPOINT uses the 8 closest GRID points to calculate an interpolated value at
the LAT/LON you request.  Using 8 points could be an issue with coarser
models as the interpolation would include grid points far removed from your
LAT/LON point.

Regards,
Evan

Business Applications Meteorologist
Weather Trends International, Inc.
Phone 610-807-3197
http://www.wxtrends.com

-----Original Message-----
From: gembud-bounces@xxxxxxxxxxxxxxxx
[mailto:gembud-bounces@xxxxxxxxxxxxxxxx] On Behalf Of Mark Hughes
Sent: Tuesday, November 17, 2009 12:48 PM
To: gembud@xxxxxxxxxxxxxxxx
Subject: [gembud] Interpolating levels in GRIB data

Hi All,

I am working with models produced from wind and temperature GRIB data.
(DCGRIB2 produces a .gem model from HT*, HU* and HV* messages).
I am trying to extract point data using GDPOINT at an arbitrary level.
Can anyone tell me how to interpolate?  Or, as an alternative, how can I
create a new grid with finer resolution in the level dimension?

Many thanks,

Mark Hughes
Global Weather Dynamics

_______________________________________________
gembud mailing list
gembud@xxxxxxxxxxxxxxxx
For list information or to unsubscribe,  visit:
http://www.unidata.ucar.edu/mailing_lists/