20000421: gempak algorithms

Bob,

In general, we only support the current 5.4 release of Gempak, but the
usage of AGR() should not have changed. Perhaps Peter Neilley has
already printed the documentation for the current release.

At any rate, if you are refering to a gridded data set, you will find the
AGE(S) function described in the GPARM vector section of chapter 3 on the
online help pages:
http://www.unidata.ucar.edu/packages/gempak/tutorial/manual/chapter3/chap3X5Fupc-37.html#HEADING37-0

In general, AGE is a parameter that can be automatically computed if the HGHT
field and U and V components of the wind exist in your gridded data set.

WND = GEO + AGE

where WND is the vector obtained from U and V components, such as UREL and VREL.
The HGHT field is necessary to compute GEO, so AGE = WND - GEO. AGE is a vector
quantity, so you can display it with a program such as gdwind or gdstream as
barbs, arrow, or streamlines- or you can contour it by creating a scalar output
quantity such as MAG(AGE) in gdcntr.

AGE is typically computed as AGE(HGHT), however, you could useother fields
such as the thickness, montgomery stream function, or some other scalar
quantity.

You should be able to view the AGE function within the gempak code 
in the file:
...../gempak/source/gemlib/dv/dvage.f

which in the current version shows:
        SUBROUTINE DV_AGE  ( iret )
C************************************************************************
C* DV_AGE                                                               *
C*                                                                      *
C* This subroutine computes the ageostrophic wind:                      *
C*                                                                      *
C*     AGE ( S ) = [ u (OBS) - u (GEO(S)), v (OBS) - v (GEO(S)) ]       *


Note...OBS is another name for WND, and S is the scalar field (HGHT)
used to compute the geostropic component, so it is assumed that
you have the 3 (UREL, VREL and HGHT) grids on the desired coordinate level
for the computation.

If you still have trouble deciphering the script, let me know.

Steve Chiswell



>From: Bob Sharman <address@hidden>
>Organization: UCAR/Unidata
>Keywords: 200004242321.e3ONLYG03513

>Your reply sounds like you've assummed I've downloaded the gempak software, wh
> ich
>I have not.  I am trying to understand a gempak script someone else has writte
> n,
>but to do that I need to know some definitions of functions.  I have an old
>version 5.1 appendix B, which does have some, but is missing the newer ones.  
> Is
>there any way I can get a copy of the relevant appendices of the user's guide
>without having to download the entire gempak package?
>Thanks
>Bob
>
>Unidata Support wrote:
>
>> >From: Bob Sharman <address@hidden>
>> >Organization: UCAR/Unidata
>> >Keywords: 200004241818.e3OIICG24445
>>
>> >OK, thanks, but how can I get a copy of these Appendices to the users
>> >guide?  I don't find them on the web site.
>> >Bob
>> >
>>
>> The users guide is provided in postscript form in the $NAWIPS/doc
>> directory of the distribution.
>>
>> Steve Chiswell
>> ****************************************************************************
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>
>