FullPos Grib files from french model ARPEGE

Hi NCL talk,

I am currently encountering a problem while trying to read grib files
from ARPEGE, which is the Meteo-France Global Spectral model. The files
are post-process by a software called FullPos that interpolates files in
physical space on a regular lat-lon grid and then converts to grib 1 format.
http://www.cnrm.meteo.fr/gmapdoc/spip.php?article17
http://www.cnrm.meteo.fr/gmapdoc/spip.php?article157

I used to work on these files with the ECMWF Metview Software.
http://www.ecmwf.int/products/data/software/metview.html

Unfortunately, reading these files with ncl proved to be difficut.
First, it provides first a warning about unknown variables, e.g.
warning:NclGRIB: Unknown grib parameter number detected (153, center 85,
table version 1 grib record 3), using default
 variable name (VAR_153)

and then the decoded fields appear to be full of 0 e.g.
Variable: PRMSL
Type: float
Total Size: 290324 bytes
            72581 values
Number of Dimensions: 2
Dimensions and sizes: [g0_lat_0 | 181] x [g0_lon_1 | 401]
Coordinates:
            g0_lat_0: [80..-10]
            g0_lon_1: [-100..100]
Number Of Attributes: 11
  center : French Weather Service - Toulouse
  long_name : Pressure reduced to MSL
  units : Pa
  _FillValue : -999
  level_indicator : 102
  gds_grid_type : 0
  parameter_table_version : 1
  parameter_number : 2
  forecast_time : 36
  forecast_time_units : hours
  initial_time : 10/01/2006 (18:00)
(0,0) 0
(0,1) 0
(0,2) 0
(0,3) 0
(0,4) 0
(0,5) 0
(0,6) 0
(0,7) 0
(0,8) 0
(0,9) 0
(0,10) 0
(0,11) 0
(0,12) 0
(0,13) 0
...

The NCEP wgrib (http://www.cpc.ncep.noaa.gov/products/wesley/wgrib.html)
software can read the header, but then complains about "complex packing"

  latlon: lat 80.000000 to -10.000000 by 0.500000 nxny 7043
          long -100.000000 to 100.000000 by 0.500000, (7043 x 1) scan 0
mode 128 bdsgrid 1
*** Cannot decode complex packed fields n=7043***

I then decided to try to mail this list as my programming experience in
grib is limited.
If you happen to need this, an example grib file may be found on
elder.mmm.ucar.edu /users/yann/GRIB/62L3_fc_GRIDHSTATOURX05+0036.grb

Thanks for help and advice!
Best regards,

Yann MICHEL

/NCL provides read-only support for data in GRIB1 and GRIB2 formats. To
open a file, you only need to know that the file is GRIB. NCL figures
out which version of GRIB is in the file and processes the file
accordingly. NCL's support for GRIB is an evolving process. As an ever
more diverse set of GRIB files have been encountered, NCL has been
improved to handle many more features of the GRIB format. However, since
GRIB has many features that are obscure enough that they have never been
encountered in practice by the NCL developers, there are still some
aspects of GRIB that NCL does not handle properly. Generally, the NCL
developers try to support features that appear in GRIB files that users
are actually using. The best way to help improve the GRIB-decoding
capabilities of NCL is to call attention to files that are important to
your work but that NCL does not seem to interpret correctly. If you have
problems reading a particular set of GRIB files, please send email to
ncl-talk_at_ucar.edu <mailto:ncl-talk_at_ucar.edu>. You will need to subscribe
<http://mailman.ucar.edu/mailman/listinfo/ncl-talk> first, if you
haven't already.

/PS here is my simple NCL script/
/;*******************************************************
load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/gsn_code.ncl"
load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/gsn_csm.ncl"
;************************************************
begin
  grb_file = addfile("62L3_fc_GRIDHSTATOURX05+0036.grb","r")
  PRMSL = grb_file->PRMSL_GDS0_MSL
  print(PRMSL)
;************************************************
; create default plot
;************************************************
  wks = gsn_open_wks("ps","ers40") ; open a ps file
  gsn_define_colormap(wks,"BlAqGrYeOrRe") ; choose colormap

  res = True ; plot mods desired
  res_at_cnFillOn = True ; turn on color fill
  res_at_cnLinesOn = False ; turn off contour lines
  res_at_gsnSpreadColors = True ; use full range of
color map

  plot = gsn_csm_contour_map_ce(wks,PRMSL(:,:),res)
end/

/

_______________________________________________
ncl-talk mailing list
List instructions, subscriber options, unsubscribe:
http://mailman.ucar.edu/mailman/listinfo/ncl-talk
Received on Thu Mar 05 2009 - 14:16:20 MST