**To**:**prescy@xxxxxxxxxxxxxxxxx****Subject**:**Re: [ferret_users] potential vorticity from OGCM****From**:**Ryo Furue <furue@xxxxxxxxxx>**- Date: Tue, 28 Jul 2009 22:04:32 -1000 (HST)
- Cc: ferret_users@xxxxxxxx
- In-reply-to: <1248783380.25921.24.camel@xxxxxxxxxxxxxxxxxxxxxxxx>
- References: <71cc5ca20907222324h695f064ah5fbf3ac7129b449f@xxxxxxxxxxxxxx> <4A69F574.8060302@xxxxxxxx> <1248783380.25921.24.camel@xxxxxxxxxxxxxxxxxxxxxxxx>
- Sender: owner-ferret_users@xxxxxxxx

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

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