[MITgcm-support] Temperature Advection Scheme : Internal Gravity Wave Simulation

[Dimitris Menemenlis]

Maybe try using Crank Nickelson time stepping with >=5 min time step.
Here is copy of old email from Ayan Chaudhuri on topic:

When we ran our tidal forcing experiments with the default timestepping scheme, we noticed weaker amplitudes mostly because the fast gravity waves were getting  damped (even with timesteps of 2 min). Crank-Nickelson overcomes that short period damping which affect the tidal solution . The 5 min recommendation is time-stepping scheme dependent (not model resolution dependent) as Crank-Nickelson does not work for large time steps. This time step limitation makes it more expensive to run and hence is not default. I don't think there are any other considerable side effects.

And probably best to use rStar if your configuration allows it.
Here is some old notes from Jean-Michel on the topic:

Regarding Crank-Nickolson (as in verification/adjustment.cs-32x32x1/input/data:
implicSurfPress=0.5,
implicDiv2DFlow=0.5,
these 2 parameters are just 1/2. You can try with 0.6 instead, but it's
no longer 2nd order (and will add some dissipation).
And there is typo in your data file since implicSurfPress is repeated 2 times
but implicDiv2DFlow is missing.

Regarding Non-Lin Free-Surf: What is the minimum depth in this domain ?
If it's not too small (e.g., at least 20.m I would say), I would advise
to start with rStar (this is sometime more stable than pure z-coord),
especially if you add tides, rStar will reduce vertical velocity
(and related spurious vertical mixing) which is associated to d.Eta/dt.
select_rStar=2,
nonlinFreeSurf=4,

> On Jun 26, 2017, at 10:00 AM, Hanut Vemulapalli <hanut2 at gmail.com> wrote:
> 
> Hi all,
> 
> I am trying to simulate gravity waves produced by an isolated gaussian topography in a uniformly stratified ocean. I have a 2D simulation with unit depth in the y-coordinate. I am applying the tidal forcing by prescribing the U-velocity at the boundaries (@Jody: Thank you for your suggestions) . I am able to simulate gravity waves, but could anyone please advice as to which temperature advection scheme would be best suited for my case and to what extent the scheme used can effect the wave field produced.
> I have tried using schemes 2,3,33 and 77 but there seems to be no difference in the wave field produced and the gravity wave beam is not sharp/poorly resolved.
> Thanks in advance. 
> 
> Best regards, 
> Hanut V


-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mitgcm.org/pipermail/mitgcm-support/attachments/20170626/ed07147a/attachment.htm>