[MITgcm-support] The criteria of cg3dMaxIters

Tue Aug 15 13:41:29 EDT 2017

Saeid, I think that these were rhetorical questions.
Oceanic eddies are not 12 degrees across and geostrophic eddies do
not generate dw/dt sufficiently large to warrant the "nonHydrostatic=.True.” flag.
If you want geostrophic eddies in your simulation, you need to configure
your simulation with 1/4-degree horizontal spacing or better (1/4-deg is marginal).
If you want to explore non-hydrostatic physics, your horizontal and
vertical grid spacing need to be of comparable order of magnitude, e.g., <~100 m.

Dimitris

> On Aug 15, 2017, at 10:16 AM, Saeid Esmaeilpour <saeidesmaeilpour at gmail.com> wrote:
> 
> Yes they have.
> 
> Saeid
> 
> On Tue, Aug 15, 2017 at 1:14 PM, Jody Klymak <jklymak at uvic.ca <mailto:jklymak at uvic.ca>> wrote:
> 
> 
> On 15 Aug 2017, at 9:58, Saeid Esmaeilpour wrote:
> 
> Thanks again Jody,
> It was really helpful, for the last question about this issue, Do I need
> nonHydrostatic=.True. for the simulation of Eddies? Isn't that a fine-scale
> phenomena? will MIT show up  Eddies at 2-degree resolution?
> 
> Do your eddies have large dw/dt?
> 
> Are they about 12-degrees across?
> 
> Cheers,  Jody
> 
> 
> 
> Thanks,
>    Saeid
> 
> On Tue, Aug 15, 2017 at 12:42 PM, Jody Klymak <jklymak at uvic.ca <mailto:jklymak at uvic.ca>> wrote:
> 
> On 15 Aug 2017, at 9:29, Saeid Esmaeilpour wrote:
> 
> Jody,
> my model is about The simulation of currents Circulation from surface to
> depth in indian Ocean, and I selected nonHydrostatic=.TRUE., cause I
> think the model resolve the Nonlinear terms with nonHydrastatic=True (am I
> wrong ?). If I select nonHydrastatic=True, in this case how much should I
> set for cg3MaxIters? and If select nonHydrastatic=False, how much for that?
> basically for the simulation of currents Circulation and at 2-degree I have
> to take non Hydraustatic=false?
> 
> nonHydrostatic=.True. solves the non-hydrostatic equation for dw/dt,
> which essentially means the pressure needs to be determined globally from a
> Poisson equation, and hence the 3-D solver. .False. means that pressure
> is solved using the hydrostatic approximation (if you don’t know what this
> is, Google plus a basic GFD course would help).
> 
> This really has nothing to do with non-linearity until you start resolving
> scales where the hydrostatic approximation breaks down (basically dw/dt is
> no longer << rho’g / rho_0).
> 
> You really only need non-hydrostatic approximation for fine-scale runs
> looking at internal waves, dense overflows, convection, or other turbulent
> phenomena. None of which will show up at 2-degree resolution.
> 
> Cheers, Jody
> 
> Thanks again,
> Saeid
> 
> On Tue, Aug 15, 2017 at 11:59 AM, Jody Klymak <jklymak at uvic.ca <mailto:jklymak at uvic.ca>> wrote:
> 
> Hi Saied,
> 
> cg3dMaxIters is only used if nonHydrostatic=.True.. You aren’t resolving
> any non-hydrostatic physics at 2-degree resolution, so I would suggest
> setting nonHydrostatic=.False. Your model runs will be *much* faster.
> 
> 
> Cheers, Jody
> 
> On 15 Aug 2017, at 8:43, Saeid Esmaeilpour wrote:
> 
> Hi Dear users,
> could someone please explain to me what are the following PARM02?
> when I increase cg3dMaxIters from 50 to 400 (e.g,. cg3dMaxIters=400) the
> run speed becomes very slowly. how can I select this value? what's the
> criteria for selecting this number? My domain is 510*210 with 20layer and
> also my resolution is 2 degree (3704m).
> 
> # Elliptic solver parameters
> &PARM02
> cg2dMaxIters=1000,
> cg2dTargetResidual=1.E-13,
> cg3dMaxIters=400,
> cg3dTargetResidual=1.E-13,
> 
> Thanks for any help,
> Saeid
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