Re: ncl_filedump and wgrib

thanks for your reply .
i read the NCL manual for how NCL process the grib file.But i
still wondering for example if NCL finds that the grib file contains several
records with the same variable name ,with the same level (ex: isobaric
level) and same dimension , differ only in time , then why it nesed to
create different variables .the algorithm of the NCL as i understand should
not permit generation of such variables.
in my grib file i have 3 variables only and here is the dump of the file
using the ncl.
sometimes these variables are misleading and confusing.
      float A_PCP_GDS0_SFC_acc ( g0_lat_0, g0_lon_1 )
      float A_PCP_GDS0_SFC_acc3h ( forecast_time2, g0_lat_0, g0_lon_1)
      float A_PCP_GDS0_SFC_acc3h_1 ( forecast_time3, g0_lat_4, g0_lon_5 )
      float NCPCP_GDS0_SFC_acc ( g0_lat_0, g0_lon_1 )
      float NCPCP_GDS0_SFC_acc3h ( forecast_time2, g0_lat_0, g0_lon_1 )
      float NCPCP_GDS0_SFC_acc3h_1 ( forecast_time3, g0_lat_4, g0_lon_1)
      float ACPCP_GDS0_SFC_acc ( g0_lat_0, g0_lon_1 )
      float ACPCP_GDS0_SFC_acc3h ( forecast_time2, g0_lat_0, g0_lon_1
      float ACPCP_GDS0_SFC_acc3h_1 ( forecast_time3, g0_lat_4, g0_lon_5 )
    i aslo have attached the dump of file using both wgrib and ncl_fildump

On Wed, Sep 28, 2011 at 11:18 PM, David Brown <dbrown@ucar.edu> wrote:

> Hi Ahmed,
>
> wgrib simply lists each record in a GRIB file in the order it finds them.
> NCL looks through the whole file and organizes the records into variables
> with time and level dimensions in addition to the horizontal lat/lon
> dimensions. But in order to add those dimensions, it needs to make sure
> that the records are compatible. GRIB has many types of level records for
> instance (e.g. sigma levels, hybrid levels, pressure levels). In order to
> create a valid level dimension, all the records used must have the same type
> of level, in addition to representing the same type of quantity. Further,
> the GRIB file can contain records with the same type of quantity but on
> different horizontal grids, with different extents or resolutions or
> projection type. These must be represented with different variables. The
> whole process that NCL uses to represent GRIB data is described in detail
> at
> http://www.ncl.ucar.edu/Document/Manuals/Ref_Manual/NclFormatSupport.shtml#GRIB.
> I hope this helps.
> -dave
>
>
> On Sep 28, 2011, at 1:31 PM, ahmed lasheen wrote:
>
> hello
> when i make wgrib for grib1 file contains precipitation data , i found
> three variables which are precipitation of grid scale , precipitation of
> convective scale and total scale precipitation.But when i make ncl_filedump
> i see 9 variables which represent those variables plus others
> related variables to them
> but different on the average time and grid location.why this occur ? and
> what this difference means between wgrib and ncl_filedump?.
> thanks in advance
>
> --
> ===============
> Ahmed Lasheen
> Junior researcher at Cairo Numerical Weather Prediction Center (CNWPC)
> Egyptian Meteorological Authority(EMA)
> Cairo,Egypt
> ===============
>
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>

-- 
===============
Ahmed Lasheen
Junior researcher at Cairo Numerical Weather Prediction Center (CNWPC)
Egyptian Meteorological Authority(EMA)
Cairo,Egypt
===============

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