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Re: [ferret_users] potential temperature to in situ temperature conversion

Thanks James,
I've put this into the Users Guide, so that next time we publish that out to the web it'll be in there.


James Orr wrote:

- It is very simple to convert potential to in situ temperature.
- To do so, you only have to use the THETA_FO function
- For details, see the message below, sent to the list last year

Ansley, might you be able to document this feature in the next version of the Ferret users guide?

Many thanks,


---------- Forwarded message ----------
From: James Orr <James.Orr@xxxxxxxxxxxx>
To: Ferret UserGroup <oar.pmel.ferret_users@xxxxxxxx>
Date: Thu, 23 Apr 2009 09:11:18 +0200 (CEST)
Subject: Re: HOw to convert potential temperature to in-situ temperature?

To convert from potential temperature to in-situ temperature it is very easy. It can be done using the existing Ferret function that does the opposite.

As documented in the Ferret user manual, the function THETA_FO is designed to convert from in-situ temperature to potential temperature (only). The arguments are

  THETA_FO( salt, temp, P, P_reference)

What is undocumented in the manual is that to do the opposite (convert in-situ to potential temperature), we only need to inverse the 3rd and 4th arguments. For example

  let Tpot     = theta_fo(35,20,5000,0)
  let Tinsitu  = theta_fo(35,19,0,5000)
  list Tpot, Tinsitu
! Results should be Tpot=19 and Tinsitu=20

This might be useful for some, e.g., ocean modelers who typically store out potential temperature fields but sometimes need in-situ temperature in post-treatments. It would be nice if this currently undocumented feature of THETA_FO would be added to the user's manual.



Old unanswered Question from Ferret archive:
    * To: ferret_users <ferret_users@xxxxxxxxxxxxxxxxxxx>
* Subject: HOw to convert potential temperature to in-situ temperature?
    * From: Yang Kun <yangk@xxxxxxxxxxxxxx>
    * Date: Fri, 25 Feb 2000 15:13:43 -0600 (CST)
    * Sender: owner-ferret_users@xxxxxxxxxxxxxxxxxxx

HI, all

I know theta_fo can calculate potential temperature.
Is there also a fuction to do the contrary thing in ferret?
Or, I have to write Fortran to do this?


On Thu, 11 Feb 2010, David Wang wrote:

Hi Ferreters,

Is there a simple way to convert potential temperature (usually from ocean model output) to in situ temperature, sort of like the inversion of the function THETA_FO?


Daiwei Wang
Department of Earth and Environmental Sciences and
Lamont-Doherty Earth Observatory
Columbia University

   James Orr
   LSCE/IPSL, Laboratoire des Sciences du Climat et de l'Environnement

   LSCE/IPSL, CEA Saclay           http://www.ipsl.jussieu.fr/~jomce
   Bat. 712 - Orme                 mailto:  James.Orr@xxxxxxxxxxxx
   Point courrier 132
   F-91191 Gif-sur-Yvette Cedex    Phone:   (33) (0)1 69 08 39 73
   FRANCE                          Fax:     (33) (0)1 69 08 30 73

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