Re: Any idea how to make out such variables

From: Dennis Shea <shea_at_nyahnyahspammersnyahnyah>
Date: Tue, 16 Oct 2007 23:25:37 -0600

guez offtsing wrote:
> I want to analyze the wind field from NCEP data.GrADs was ever used.
> Somehow the variable names decomposed from grb files in NCL are quite
> different to ones in GrADs.
> In GrADs, I can get more information from the corresponding ctl file.
> While in NCL, where or which command can help me understand them?
> For example,
> V_GRD_3_PVL_10
> What is the meaning of abbr. PVL, and the number "10"?
>
>
===================================================

NCL can read GRIB-1 and GRIB-2 files directly.
There is no need for a ctl file. You can view the contents
of any GRIB-1, GRIB-2, netCDF, HDF or HDF-EOS file via
ncl_filedump and create to netCDF via ncl_convert2nc

http://www.ncl.ucar.edu/Document/Tools/ncl_filedump.shtml
http://www.ncl.ucar.edu/Document/Tools/ncl_convert2nc.shtml

ncl_filedump is analogous to the Unidata utility ncdump.
This allows users to view the files entire contents.
NCL also provides value added information like latitude
and longitude arrays.

===================================================
A complicated but complete description of NCL's automatic
name generation for GRIB is at:
 
http://www.ncl.ucar.edu/Document/Manuals/Ref_Manual/NclFormatSupport.shtml#GRIB
=====

[1]
NCL uses a netCDF variable model. netCDF files require that all
variable names be unique on a file. Hence when NCL opens a GRIB
file it creates unique names. The 1st part [eg, U or V or TMP...]
is created based on the GRIB parameter table.
[2]
GRIB is a record format not a file format. When multiple GRIB
records are written to a file, there are no rules on the file's
contents. The same variable [say, TMP] may be available on the file
as on pressure level, hybrid levels, sigma, ...; it can be available
on different grids [one dimensional lat/lon, multidimensional
lat/lon]; other variations are also possible.
[3]
Look at the "long_name" and "units" attributes of the variable
V_GRD_3_PVL_10 when you do an ncl_filedump; look at the lat/lon
coordinates, etc

This will tell you all you need to know.

===
I suggest that you download an read the
Language min1-Reference manual [pdf] at
http://www.ncl.ucar.edu/Document/Manuals/

good luck

D

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Received on Tue Oct 16 2007 - 23:25:37 MDT

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