From: Dennis Shea <shea_at_nyahnyahspammersnyahnyah>

Date: Mon Nov 09 2009 - 14:03:24 MST

Date: Mon Nov 09 2009 - 14:03:24 MST

Please note: tThe 1st rule of data processing is to *look at your data*.

[1]

The calculation of potential vorticity requires a vertical derivative.

You have:

a = addfile("uwnd.2005.nc","r")

u = short2flt(a->uwnd(152,{200},:,:))

which means you are reading in the 153rd time step and the 200hPa level

only.

In fact, you have only a two-dimensional array: u(lat,lon). The same holds

for temperature and v. So, you do not have multiple vertical levels.

Hence,

a vertical derivative in not possible!!

Use

printVarSummary( u )

to verify.

The actual data variables are: (time, lev,lat,lon)

[2]

There were many syntax errors which you did not even try to correct.

Please do not send us code with multiple syntax errors.

We like to help but *** our time is valuable too!!!! ***

[3]

Please read the Mini-Language manual at:

http://www.ncl.ucar.edu/Document/Manuals/

[4]

The approximation you were using is good only on isentropic surfaces.

The formulation

for pressure levels is significantly different.

I have a PV code which I will send you offline.

*NOTE* the is unsupported. I will not answer any questions.

kalim ullah wrote:

*> Dear Wei,
*

*> I am feeling difficulty to calculate the potential vorticity as you
*

*> suggested me. Now I am sending you my script file I hope you will
*

*> check it and suggested me like before.
*

*> thanks in advance
*

*> kalim
*

*>
*

*> --- On *Mon, 10/19/09, Wei Huang /<huangwei@ucar.edu>/* wrote:
*

*>
*

*>
*

*> From: Wei Huang <huangwei@ucar.edu>
*

*> Subject: Re: how to calculate potential vorticity
*

*> To: "kalim ullah" <kalimrid@yahoo.com>
*

*> Date: Monday, October 19, 2009, 7:09 AM
*

*>
*

*> Kalim,
*

*>
*

*> Where "phi = latitude * PI/180".
*

*> Do not scale your vrt before pv, but after you get pv.
*

*>
*

*> Assume your have KZ levels,
*

*>
*

*> where theat = T * (100000/p) **(R/cp).
*

*>
*

*> then:
*

*> at level 1: d(theta)/dp = (theta(2) - theta(1))/(P(2) - P(1))
*

*> at level KZ: d(theta)/dp = (theta(KZ) - theta(KZ -1))/(P(KZ) -
*

*> P(KZ -1))
*

*> and other levels: d(theta)/dp = 0.5 * ( (theta(K+1) -
*

*> theta(K))/(P(K+1) - P(K))
*

*>
*

*> + (theta(K) - theta(K-1))/(P(K) - P(K-1)))
*

*>
*

*> Where P is in Pa.
*

*>
*

*> Hope this help.
*

*>
*

*> Wei Huang
*

*> huangwei@ucar.edu
*

*> <http://us.mc537.mail.yahoo.com/mc/compose?to=huangwei@ucar.edu>
*

*> VETS/CISL
*

*> National Center for Atmospheric Research
*

*> P.O. Box 3000 (1850 Table Mesa Dr.)
*

*> Boulder, CO 80307-3000 USA
*

*> (303) 497-8924
*

*>
*

*>
*

*>
*

*>
*

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Received on Mon Nov 9 14:03:04 2009

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