[Fwd: RE: [MITgcm-support] grid-scale noise in 1/4-deg model]
Alistair Adcroft
adcroft at MIT.EDU
Wed Dec 3 10:45:25 EST 2003
Ichiro,
The quoted numbers must be for vertical viscosity? 1e-3 is way too small for
horizontal bi-harmonic viscosity. Send me the data file for the bi-harmonic
run -less ambiguous that way.
You can subscribe to the list by following the link on the home page:
http://mitgcm.org/ but you don't have to subscribe to use it.
A.
--
Dr Alistair Adcroft http://www.mit.edu/~adcroft
MIT Climate Modeling Initiative tel: (617) 253-5938
EAPS 54-1523, 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 Ichiro Fukumori
Sent: Tuesday, December 02, 2003 6:48 PM
To: Alistair Adcroft
Cc: tlee at pacific.jpl.nasa.gov; mitgcm-support at mitgcm.org
Subject: Re: [Fwd: RE: [MITgcm-support] grid-scale noise in 1/4-deg model]
Alistair,
The biharmonic friction is set at 1.e-3. The model blew up when we tried
2.e-3 or 5.e-3. Should we make it smaller?
From the behavior of changing biharmonic friction and to kill the noise, I
thought of trying a large Laplacian friction which I thought would have a
wider ranger of stable frictional values. We've ran the model with
Laplacian viscosity of 100 and 200 (m^2/s) with cosPower=2 without
biharmonic friction. Case with 200 is clearly much more diffusive than
biharmonic with 1.e-3, but the grid-scale noise is still present.
KPP parameters displayed similar grid-scale noise. So we turned horizontal
smoothing of KPP parameters on, but the noise is still present. KPP noise
must be a consequence of the grid-scale noise and not the cause.
We do have bottom friction on;
no_slip_sides=.TRUE.,
no_slip_bottom=.TRUE.,
bottomDragQuadratic = 0.002,
in the data file. Could we have a problem in particular advection
scheme we are using? We've got;
tempAdvScheme=4
saltAdvScheme=4
multiDimAdvection=.FALSE.,
staggerTimeStep=.TRUE.,
How about CD scheme? We don't have it on, but we tried turning it on cold
turkey, setting D-grid velocity to zero, but the grid-scale noise was still
present after 30-days of integration.
Any suggestions?
-- Ichiro
PS. I am not on the mitgcm-support mailing list. Can I be included? Would I
want to be included?
At 03:24 PM 12/2/2003 -0800, Dimitris Menemenlis wrote:
>-----Forwarded Message-----
>From: Alistair Adcroft <adcroft at MIT.EDU>
>To: mitgcm-support at mitgcm.org
>Subject: RE: [MITgcm-support] grid-scale noise in 1/4-deg model
>Date: Tue, 02 Dec 2003 17:10:56 -0500
>
>Ichiro,
>
>For the left column runs (bi-harmonic) were you using the maximum
>allowed viscosity? It's worth finding the upper limit on numerical
>viscosity before the model is unstable. My preferred recipe is to use
>0.1 of this value - this damps the grid scale noise one e-folding scale
>every 10 steps and damps the 2-dx wave only every 160 steps. I think
>the relevent expression is something
>like:
> A_4 * dt * cos(phi_max)^m * pi^4 [ 1 / dx(phi_max)^2 +
>1/dy(phi_max)^2 ]^2 < 1 assuming the expression is maximized at the
>northern edge of the domain. The choice of "m" can change that.
>
>Do you have bottom friction turned on?
>
>A.
>--
>Dr Alistair Adcroft http://www.mit.edu/~adcroft
>MIT Climate Modeling Initiative tel: (617) 253-5938
>EAPS 54-1523, 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 Ichiro Fukumori
>Sent: Monday, November 24, 2003 9:41 PM
>To: cnh at mit.edu; adcroft at ocean.mit.edu; support at mitgcm.org; Armin
>Koehl; Detlef Stammer
>Cc: tlee at pacific.jpl.nasa.gov; bnc at pacific.jpl.nasa.gov
>Subject: [MITgcm-support] grid-scale noise in 1/4-deg model
>
>
>Dear Colleagues,
>
>We are experiencing grid-scale noise in our global 1/4-deg model
>simulation. It does not appear to be a lack of horizontal friction.
>Would you have any idea what may be the problem? My suspicion is that
>this may have something to do with some vertical process. Places with
>prominent noise are adjacent to coastal boundaries (where there's
>upwelling) and places with deep mixed layers.
>
>Attached are 2 plots comparing model output of two runs at two
>different locations. Each page shows a 101x101 grid point area. Plot
>n03d_1.ps is surface layer along the west coast of Africa (centered
>13.8E, 19.4S) and the other (n03d_2.ps) is Kuroshio extension area
>(centered 170.1E, 28.9N) at 350m depth. The three rows are, from the
>top, zonal velocity (u, m/s), meridional velocity (v, m/s), and
>temperature (T, degC). The left column is a run that employs
>biharmonic friction (1.e10 m^4/s) and is at day 123 of 1992. The right
>column used Laplacian friction (200 m^2/s) and is at day 69 of 1992.
>
>In n03d_1.ps, the noise appears along the coast (land is shown in
>gray), especially in u & v of the right column (Laplacian friction
>run).
>
>In n03d_2.ps, the noise is severe in u & v in the left column in the
>northern half, just south of the Kuroshio.
>
>All results are 3-day averages.
>Could these noise be due to an absence of the CD scheme? What else
>could cause such noise? We would appreciate any suggestions you may
>have.
>
>Thanks, Ichiro
>
>
>===============================================================
>Ichiro Fukumori | Jet Propulsion Laboratory
>e-mail: fukumori at jpl.nasa.gov | Mail Stop 300-323
>phone: +1 (818) 354-6965 | 4800 Oak Grove Drive
>fax: +1 (818) 393-6720 | Pasadena, California 91109, U.S.A.
>===============================================================
>
>
>_______________________________________________
>MITgcm-support mailing list
>MITgcm-support at mitgcm.org
>http://dev.mitgcm.org/mailman/listinfo/mitgcm-support
>--
>Dimitris Menemenlis <menemenlis at jpl.nasa.gov>
>Jet Propulsion Lab, California Insitute of Technology
>MS 300-323, 4800 Oak Grove Dr, Pasadena CA 91109-8099
>tel: 818-354-1656; fax: 818-393-6720
===============================================================
Ichiro Fukumori | Jet Propulsion Laboratory
e-mail: fukumori at jpl.nasa.gov | Mail Stop 300-323
phone: +1 (818) 354-6965 | 4800 Oak Grove Drive
fax: +1 (818) 393-6720 | Pasadena, California 91109, U.S.A.
===============================================================
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