[MITgcm-support] Re: problem higher order advections schemes

[Martin Losch]

Jean-Michel,

thanks, I guess that explains some of my problems. So appearently my 
intial temperature and velocity are not in geostrophic balance, 
although I tried to get this approximately right. But the intial 
adjustment is so strong that it there feed backs occur. The next thing 
I'll try is a horizontally homogeneous stratification. According to 
your tests, there shouldn't be any problems with configuration and 
advection scheme 33, 77, etc, should it?

Anyway, I'll keep you posted.

Martin

On Tuesday, September 23, 2003, at 04:09 PM, Jean-Michel Campin wrote:

> Hi Martin,
>
> After further investigation, I have the impression that
> this set-up is very sensitive to any local perturbation in the
> vertical diffusion.
> To summarize: with advection scheme 2 or 4, every thing
> remains stable (after the initial adjustment (~ 1 month) CFL_v,w < 
> 2.e-4)
> and the initial stratification is preserved.
> with advection scheme 30, 33, 77 Super-Bee (and multiDim as default),
> I get strong mixing due to high vertical velocity (max_CFL_v > 0.02
> & max_CFL_w > 0.1 ).
> This is very sensitive because when I use the advection scheme 77
> but changed to Lax-Wendroff, the max Temp start to decrease
> almost immediately (with strong W) if I use multiDim but much later
> (after > 2 month) if I use multiDim=.FALSE.
>
> Could this high sensitivity be related to
> Coriolis on C grid with not enough horizontal viscosity ?
> (note that all remain perfectly zonally symetric, included W).
>
> It is clear that it's related to dynamical feedback, so I decided to
> use the stagger time-stepping option and, guess what, it works nicely
> and the initial stratification  is preserved
> with 77 Lax Wendroff & SuperBee, 30 and also 33 !
>
> Hope this will help.
>
> Cheers,
>
> Jean-Michel
>
> PS: 2 little things:
> a) the minimum temperature is slightly below the initial minimum
> and is still decreasing after 1 year, but tends to be lower when I use 
> KPP
> compared to the simple case with convective adjustment 
> (ivdc_kappa=100).
> b) I tried z* and get perfect global conservation of total heat 
> content.