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19990713: PVOR potential vorticity for THETA and PRES
- Subject: 19990713: PVOR potential vorticity for THETA and PRES
- Date: Tue, 13 Jul 1999 10:58:27 -0600
>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