RE: [ferret_users] calculating pressure from a reference depth

[Jaclyn Brown <jaclyn.brown@xxxxxxxx>]

Aha, it wasn't the pressure calculation I was doing wrong after all!

I was calculating pressure from density, then taking the x-derivative, and
then depth integrating. All these different constraints on z were too much
for ferret to handle at once, so I saved intermediate steps along the way. 

Thanks,
Jaci

-----Original Message-----
From: owner-ferret_users@xxxxxxxx [mailto:owner-ferret_users@xxxxxxxx] On
Behalf Of william s. kessler
Sent: Wednesday, August 01, 2007 6:53 PM
To: Jaclyn Brown
Cc: Ferret Usergroup
Subject: Re: [ferret_users] calculating pressure from a reference depth

Hi Jaci -

The right way to do this is to test (part of) the result after doing  
the calculation! One good test, as you suggest, is that dp/dx is zero  
at the reference level. Another is to list the results of a @iin and  
the down-index operation on single profile and check it directly to  
be sure that it is doing what you expect.

I think the resolution of the discussion you link to is that @iin is  
correct in reverse but @rsum may not be as expected. Steve and Ryo  
hashed this around in that thread. Also see my comment about how to  
make @rsum more consistent at the end of the thread, in:

http://www.pmel.noaa.gov/maillists/tmap/ferret_users/fu_2006/ 
msg00482.html

Of course, if you just need the pressures at a particular level, you  
don't need to do the down-index integration, just @din within  
whatever limits.

Billy K

On 1Aug 2007, at 2:46 PM, Jaclyn Brown wrote:

> Hi,
>
> I need to calculate some horizontal pressure gradients. To do this  
> I've been calculating pressure by integrating density from a  
> particular reference depth. I'm not sure I'm doing it correctly  
> because of the problems with doing @iin in reverse - seehttp:// 
> www.pmel.noaa.gov/maillists/tmap/ferret_users/fu_2006/msg00478.html  .
>
> Has anyone figured out the right way to do this so that dp/dx is 0  
> at the reference depth?
>
>
>
> Thanks for your help,
>
> Jaci
>
>
>
> Dr Jaclyn Brown
>
> Postdoctoral Associate
>
> Dept Geology and Geophysics
>
> Yale University
>
>
>
> Ph. 203 432 1959
>
>
>
> PO Box 208109
>
> New Haven CT 06520
>
> USA
>
>
>
>