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20030106: Gempak/ Nogaps model variables query



John,

The GRIB parameter conversions you will be referencing are 
in the $GEMTBL/grid directory. In these tables, when you see
a quantity with "--" as 2 characters, this will be replaced
by the accumulation period (or 00 at initialization), or "XX" 
generally for the period of instantaneous quantity or
unspecified accumulation period. Eg:

059 Precipitation rate                kg m**-2 s**-1       PR--  
061 Total precipitation               kg m**-2             P--M 
062 Large scale precipitation         kg m**-2             S--M  
063 Convective precipitation          kg m**-2             C--M   


If for example the model is outputting 6 hour accumulations,
you will see:
PRXX, P06M, S06M and C06M at f006. If the NOGAPS fields are
all XX even at forecast hours, then the grib data isn't using
the accumulation period of the PDS time units.

The P--M is the total precipitaion, whereas the S--M and C--M
are the portion related to convective or gridscale processes and 
largescale or stratiform processes respectively. The Convective
portion of the precipitation is usually very dependent on the
cumulus parameterization and cloud physics of the model run. The 
precipitation quantities ending in M are equivalent to "mm". The 
accumulation period is typically 6 or 12 hours for the larger scale 
models (and the grid library will compute the 06 quantities in between
the forecast hours....eg when f006 P06M and f012 P12M, the
P06M is from f000 to f006, and P12M is from f000 to f012,
if P06M isn't provided at f012, it will be calculated from
P12M-P06M) for f012.

For the cloud quantities, you should be looking at percentages
accoring to the wmo:
071 Total cloud cover                 %                    CLD     
072 Convective cloud cover            %                    CCLD   
073 Low cloud cover                   %                    CLDL 
074 Medium cloud cover                %                    CLDM
075 High cloud cover                  %                    CLDH

Steve Chiswell


The Precipitation quantities you  will find in the 
>From: John Merrill <address@hidden>
>Organization: University of Rhode Island
>Keywords: 200301062119.h06LJxt09296

>
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>Hello, Steve:
>   I've gone back to the archive of GRIB files for the nogaps model
>fields which Greg Stossmeister
>built as the data flowed in during the ACE-Asia project. He had run a
>script to create Gempak files
>from these fields, but they didn't have all I wanted, so despite the
>lateness of the hour and the effort which
>this is going to take, I'm going to keep my programmer busy going
>through the data and cranking out an
>entirely new set of .gem files, keeping only "analysis" and "0600"
>forecasts, to give a complete time line.
>   Anyway, there are a couple of variables I am not used to working
>with, but I would like to understand.
>There are CLD, CLDL and CLDH. I can figure these out: total clouds, low
>and high clouds. I'm not sure
>how to use them in Gempak, but I'll try contouring them as percentages.
>More intriguing is CXXM, and
>I wonder if that's what the GRIB file referred to as the Convective Mass
>Fraction. How can I find
>out more about this, and just as importantly, utilize it in Gempak? I
>believe it to be a column integrated
>fractional mass flux by convection - and while I know that such model
>products don't typically "verify
>well," I'd like to have a look at what the model thinks is happening in
>this regard. Perhaps all I need to
>do is look at this with gdlist, and then try contouring it. If you have
>any prior knowledge I'd appreciate
>your insights. Thanks for any help you can provide.          John
>
>--
>
>John Merrill                                     Telephone:  401-874-6715
>Graduate School of Oceanography, URI             Fax:        401-874-6898
>
>
>
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>Hello, Steve:
><br>&nbsp;&nbsp; I've gone back to the archive of GRIB files for the nogaps
>model fields which Greg Stossmeister
><br>built as the data flowed in during the ACE-Asia project. He had run
>a script to create Gempak files
><br>from these fields, but they didn't have all I wanted, so despite the
>lateness of the hour and the effort which
><br>this is going to take, I'm going to keep my programmer busy going through
>the data and cranking out an
><br>entirely new set of .gem files, keeping only "analysis" and "0600"
>forecasts, to give a complete time line.
><br>&nbsp;&nbsp; Anyway, there are a couple of variables I am not used
>to working with, but I would like to understand.
><br>There are CLD, CLDL and CLDH. I can figure these out: total clouds,
>low and high clouds. I'm not sure
><br>how to use them in Gempak, but I'll try contouring them as percentages.
>More intriguing is CXXM, and
><br>I wonder if that's what the GRIB file referred to as the Convective
>Mass Fraction. How can I find
><br>out more about this, and just as importantly, utilize it in Gempak?
>I believe it to be a column integrated
><br>fractional mass flux by convection - and while I know that such model
>products don't typically "verify
><br>well," I'd like to have a look at what the model thinks is happening
>in this regard. Perhaps all I need to
><br>do is look at this with gdlist, and then try contouring it. If you
>have any prior knowledge I'd appreciate
><br>your insights. Thanks for any help you can provide.&nbsp;&nbsp;&nbsp;&nbsp
> ;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
>John
><pre>--&nbsp;
>
>John Merrill&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
> &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp
> ;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Tel
> ephone:&nbsp; 401-874-6715
>Graduate School of Oceanography, URI&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
> &nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Fax:&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
>  401-874-6898</pre>
>&nbsp;</html>
>
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