**To**:**"William S. Kessler" <william.s.kessler@xxxxxxxx>****Subject**:**Re: [ferret_users] potential vorticity from OGCM****From**:**prescilla kurien <prescy@xxxxxxxxxxxxxxxxx>**- Date: Fri, 31 Jul 2009 07:57:44 +0900
- Cc: Ryo Furue <furue@xxxxxxxxxx>, Ferret users <oar.pmel.ferret_users@xxxxxxxx>
- In-reply-to: <0C6547F7-1D5B-4087-8546-0626E5681748@xxxxxxxx>
- References: <71cc5ca20907222324h695f064ah5fbf3ac7129b449f@xxxxxxxxxxxxxx> <4A69F574.8060302@xxxxxxxx> <1248783380.25921.24.camel@xxxxxxxxxxxxxxxxxxxxxxxx> <20090728.220432.190528678.furue@xxxxxxxxxx> <0C6547F7-1D5B-4087-8546-0626E5681748@xxxxxxxx>
- Sender: owner-ferret_users@xxxxxxxx

Hi William and Ryo, I forgot to keep MKS units. My program works fine now. Thank you very much your comments. Prescilla On Wed, 2009-07-29 at 06:57 -0700, William S. Kessler wrote: > What Ryo said, exactly. > > But if you still think you're not getting the right answer, look at > the pieces before assembling them: > Is the relative vorticity reasonable? (shade it and overlay velocity > vectors to check) > > One thing that worries me a little is the use of SET REGION, > including for K. Is that causing a problem when you are taking a > vertical derivative? Are the vertical grids the same for all quantities? > If the other pieces look right, then try removing SET REGION/K=10, > defining the vertical derivative manually ((density[k=9]-density > [k=11])/2*<your interval>), and specifying zeta[k=10]. > > And you omitted the most important thing when using SET REGION in a > script: > > The final line: CAN REG/ALL > > It is far too easy to get an incorrect result when leftover REGIONS > are defined and you have forgotten that they remain. For example, if > K=10 remained specfied and you later did a vertical integral of > something else, you would get the wrong answer and not know it. I > never use SET REGION! It is straightforward to make the specification > within the calculation, or within the definition of variables. A > further reason to do this is that the JNL files are easier to > understand later if the region specifications are done in the > calculation, rather than somewhere far above it the listing. > > One man's opinion. > > Billy K > > > On 29 Jul 09, at 1:04 AM, Ryo Furue wrote: > > > Hi Prescilla, > > > > | The code I prepared is as below > > | > > | use 2014_hori_U_AM500_AH250.nc > > | use 2014_hori_V_AM500_AH250.nc > > | set region/X=78E:94E/Y=6N:23N/L=8/K=10 > > | use density.nc > > | LET zeta=(VVEL[d=2,x=@ddc])-(UVEL[d=1,y=@ddc]) ! relative vorticity > > | let deg2rad=(2*3.14)/360 > > | let omega = 7.292e-5 > > | let f=2*omega*sin(deg2rad*Y[g=UVEL[d=1]]) !planetary V > > | let rho_zero=1026 ! referece density > > | let grad=DENSITY[z=@ddc] ! density gradient > > | fill (grad*(zeta+f))/rho_zero > > > > Looks good to me, if DENSITY, VVEL, and UVEL are in MKS units. > > A potential (minor) problem is that if DENSITY, VVEL, and UVEL > > are defined on different grids, then it's better to map them on > > to a common grid before the final multiplication; for example > > > > let pv = grad[g=zeta] * (zeta + f) / rho_zero > > > > Density should be a potential density but I don't think > > that matters much for the upper ocean. > > > > By the way, I have a very minor piece of advice, which isn't > > related to the cause of your problem. I think it's better > > not to throw away precision gratuitously: I would write > > something along the lines of > > > > let pi = 4*atan(1.0) !! or acos(-1.0) > > let deg2rad = pi/180 > > let omega = 2*pi/(24*60*60) > > > > Regards, > > Ryo >

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**Re: [ferret_users] how to calculate growth rate of a variable***From:*Ansley Manke

**[ferret_users] potential vorticity from OGCM***From:*prescilla kurien

**Re: [ferret_users] potential vorticity from OGCM***From:*Ryo Furue

**Re: [ferret_users] potential vorticity from OGCM***From:*William S. Kessler

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