[MITgcm-support] grid-scale noise in 1/4-deg model

[Ichiro Fukumori]

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.
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