[MITgcm-support] advection scheme for T/S

[Martin Losch]

Hi Jean-Michel, Samar,

as far as I remember: after your email, I put this problem aside and in 
fact, I don't remember that I have seen this channel directory, nor the 
results. What I described yesterday, was the same problem that 
Jean-Michel's 1-y-old email replies to. So Samar, I take everything 
back. If you do things without thinking, as I did, you get the problems 
I described yesterday. But if you follow Jean-Michel's and Alistair's 
advice, you should not get the efficient vertical mixing. Sorry for the 
confusion.

Martin

On Sep 20, 2004, at 10:38 PM, Jean-Michel Campin wrote:

> Hello Martin,
>
>> Samar,
>>
>> my experience with DST3 and the flux limited 2nd order scheme (77) is
>> similar. Starting from a stable stratification with some noise to 
>> start
>> an eddy field in zonal channel with zonal wind forcing and meridional
>> buoyancy flux gradient, I get a solution, in which the isopycnal 
>> slowly
>> rise and out-crop according to wind and buoyancy forcing, when I use
>> the default 2n order scheme (2). With DST3 with flux limiting (33) and
>> 2n order with flux limiting (77), the first thing that happens is that
>> the channel gets homogenized vertically and then the expected solution
>> starts to develop. But of course, because of the initial mixing, the
>> steady state is very different from the case with the default 
>> advection
>> scheme. I have refrained from using 33 or 77 for temperature and
>> salinity since. (o:
>>
>> Martin
>
> I though this ploblem has been fixed : a uniform stratification + noise
> that gets rapidly homogenized vertically when using advec.scheme=33 or 
> 77
> I look to the MITgcm-support archive, and find this e-mail that I sent
> a year ago, but didn't find anything later (may-be
> the discussion switch to the devel list ?):
>
>> [MITgcm-support] Re: problem higher order advections schemes
>> Wed Sep 24 17:21:04 EDT 2003
>> Hi Martin,
>>
>> Didn't do any other test, but thinking to what causes
>> this strange and very different behavior of
>> those advection schemes (77 30 & 33), it could simply due to the
>> fact that they are not using the Adams-Bashforth
>> making the internal wave mode completely explicit (and
>> therefore unstable), unless you turn on the stagger timestep option.
>> Might be as simple as that.
>>
>> So, Alistair and me strongly recommand to use the stagger timestep
>> option with any of those advection scheme.
>>
>> See you,
>>
>> Jean-Michel
>
> And then I find a directory called "channel", about 1 yers old,
> and run again a set-up with advection scheme 77 for T & S,
> T=active, S=passive:
> initial fields for S = T_noise = a stratified Temperature field, with
> a front in the Y direction (quasi zonal), with very small noise added.
> a) run without staggerTimeStep, T_initial = zonal average of T_noise
> b) same as (a) with staggerTimeStep,
> c) same as (b) but T_initial = T_noise
>
> results of 1.y integration:
> a) produces the expected instability that mixes quiet efficiently
> the channel, and strongly affects the stratification.
> b) and c) work nicely and preserve the statification.
>
> Could you clarify the things (what is still a problem and what
> In summary, Can you clarify the problem you find and mention to Samar,
> and is it something new or that has already been explained before
> (I don't remember very well).
>
> Thanks,
>
> Jean-Michel