Re: ncl_filedump and wgrib

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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Received on Wed Sep 28 14:18:17 2011