Re: [ferret_users]:potential density and temperature

["William S. Kessler" <William.S.Kessler@xxxxxxxx>]

Potential density is always relative to some depth, usually 0. It is  
the density a parcel of water would have if raised or lowered  
adiabatically to the reference depth. Therefore, it is computed "as  
if" it was at the reference depth, not the full z axis.

The problem is in the last line. Replace Z[G=poTEMP] with 0 and this  
will be correct. You have correctly found the potential temperature  
at the surface, now you must be consistent and find the potential  
density in the same way.

Even so, the difference between potential and insitu density is not  
large at depths of 500m or less.

Billy K

On Sep 28, 2006, at 3:54 PM, Xavier Couvelard wrote:

> Hi all,
>
> I've got some Temperature and salinity data (from CARS2006).
>
> Id'like to compute potential density, so i just have to compute rho
> using rho_un with the potential temperature. is it ok?
>
> so i compute potential temperature with THETA_FO, but when i  
> compare rho
> and rho_pot i don't find much différence.
>
> my script is:
>
> use temperature_cars2006a.nc
> use salinity_cars2006a.nc
> let salt=mean[d=2]
> let temp=mean[d=1]
> let rho=rho_un(salt,temp,Z[G=poTEMP])
> let potemp=THETA_FO(SALT,TEMP,Z[G=TEMP],0)
> let rhop=rho_un(salt,potemp,Z[G=poTEMP])
>
>
>  what do you think of it?
> whats wrong with my script? may by reference level?
>
> thanks
>
> Xavier