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19990713: PVOR potential vorticity for THETA and PRES

>From: John Knox <address@hidden>
>Organization: .
>Keywords: 199907131559.JAA22150

>Dear Support,
>
>We've got another relatively simple question.  We need to 
>be precise in our calculation of potential vorticity.  
>While there are several options for calc'g PV, we need to 
>know exactly how PVOR is doing its calculations.  Where do 
>we look in the code for these details?
>
>Thanks for your earlier help; we were able to clear up a 
>long-standing problem with the calculation of divergence 
>tendency.
>
>Sincerely,
>
>John Knox
>address@hidden
>
>

John,

The grid diagnostic function calculations are shown in Appendix B of the
User Guide, and the code for calculating PVOR is found in:
$GEMPAKHOME/source/gemlib/dv/dvpvor.f


Here is the function header:
        SUBROUTINE DV_PVOR ( iret )
C************************************************************************
C* DV_PVOR                                                              *
C*                                                                      *
C* This subroutine computes the potential vorticity in a layer from     *
C* scalar (thermal and pressure) and vector (wind) fields:              *
C*                                                                      *
C*     PVOR ( s, V ) = - GRAVTY * AVOR ( VLAV (V) ) * LDF ( CTA ) /     *
C*                  ( 100 * LDF ( PRES ) )                              *
C*                                                                      *
C*                  Where: 100 converts millibars to Pascals            *
C*                         CTA can be THTA, THTE, or THES               *
C*                                                                      *
C* PVOR works on a layer in THTA or PRES coordinates.  In the case of   *
C* PRES, the vorticity of the layer averaged wind is corrected by       *
C* the addition of ( k cross partial V w.r.t. CTA ) dot grad (CTA).     *
C* PVOR generates a scalar grid.                                        *


Steve Chiswell