[MITgcm-support] linear EOS and Tref

[Alistair Adcroft]

Jean-Michel,

What did I say to you yesterday about Martin?

:-)

A.
--
Dr Alistair Adcroft            http://www.mit.edu/~adcroft
MIT Climate Modeling Initiative        tel: (617) 253-5938
EAPS 54-1624,  77 Massachusetts Ave,  Cambridge,  MA,  USA

-----Original Message-----
From: mitgcm-support-bounces at mitgcm.org
[mailto:mitgcm-support-bounces at mitgcm.org] On Behalf Of Martin Losch
Sent: Thursday, August 26, 2004 8:43 AM
To: Jean-Michel Campin
Cc: MITgcm Support
Subject: Re: [MITgcm-support] linear EOS and Tref


Jean-Michel, Alistair,
I am soo stupid. I am sorry I bothered you with this. Because I am only 
interested in my statistical higher order moments, I never really 
looked at the actual fields T and W. Now it turns out that they are 
almost exactly the same between different experiments (due to finite 
round off), as they should. I should have checked that much earlier. What
was the problem: I want second, third, and fourth order moments so I save
things such as 
timeaverages of theta, theta^2, theta^3, etc. To compute the moments I 
have to do this:
2nd moment = <theta^2> - <theta>^2
3rd moment = <theta^3> - <theta>^3 - 3<theta><theta^2>
etc. Well, and what happens when you don't save your variables in 
double precision and then substract large numbers from each other? Yes, 
you are left with numerical noise. I have had this before with the 
variance of bottom pressure for the Boussinesq work, do you remember? 
Anyway, thanks for having a look, and ALWAY SAVE YOUR VARIABLES IN 
DOUBLE PRECISION!!!

Puzzle solved,
Martin

On Aug 26, 2004, at 5:27 AM, Jean-Michel Campin wrote:

> Hi Martin,
>
> As you mentioned, you should get the same results (not identical
> results, because I don't expect to have the same truncation error in 
> both cases) in the ~.1oC  and ~3.oC initial temp. runs. So, there is 
> something strange.
>
> Now, to rule out some hypothesis (e.g., advection scheme ???), what
> happens if you change Tref so that you have the same T-Tref as in the 
> 1rst run (meaning, setting Tref= 3+1-.1 =3.9 ?) ? I guess you will 
> reproduce the initial solution, but I think it's worth to check.
>
> Cheers,
>
> Jean-Michel

_______________________________________________
MITgcm-support mailing list
MITgcm-support at mitgcm.org
http://dev.mitgcm.org/mailman/listinfo/mitgcm-support