morteza Miri morteza.miri at ymail.com
Sat Dec 8 14:19:33 EST 2012

```hi
I am a
student Climatology.
Wanted to
grads script calculate potential vorticity. With an example for 20 jun 1962,level
500hp. I need to have the
potential vorticity data.Where can I get?
I need potential vorticity datafor pressure level .

but Site (ncep/ncar)
data are sigma levels.
How I can convert variables in sigma to
pressure
for nc data?
6e +06 or-5e
+06 What Analysis is the the potential vorticity maps?

**Let me to consider an exact level for computing PV
**The script looks like This:
****** Open the zonal
and meridional wind, temperature and it calculates Potential Vorticity
(PV)
'reinit'
'sdfopen uwind1962jun10.nc'
'set
defile 1'
'define
u = uwnd'
'sdfopen vwind1962jun10.nc'
'set
defile 2'
'define
v = vwnd'
'sdfopen air1962jun10.nc'
'set
defile 3'
'define temp = air'
'set time 10jun1962'
'set
lat 0 88'
'set lon -19 120'
'set lev 500'
* ##########
Coriolis calculation
'define coriol=2*7.29e-5*sin(lat*3.1415/180)'
*
########## Relative Vorticity calculation
'define vort =
hcurl(u,v)'
* ########## Potential Temperature (theta)calculation

'define
dt=temp(z-1)*pow(1000/lev(z-1),0.286)-temp(z+1)*pow(1000/lev(z+1),0.286)'

'define
dp=100*(lev(z-1)-lev(z+1))'
* ########## differential of
theta/pressure
'define dtdp=dt/dp'
* ########### PV calculation
on pressure surface
'define pv = -9.8*(coriol+vort)*dtdp'
'set
gxout contour'
'd pv'
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