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

```Yes.

- 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,

Jim

---------- 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.
```
Thanks,

Jim

-----------------------------------------------------------
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?
Thanks.

yours,
Kun

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?
```
Thanks,
David

--
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
CEA-CNRS-UVSQ

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Point courrier 132
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======================================================================

```

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