[MITgcm-support] advection of passive tracers, a never-ending story

[Martin Losch]

Hi there,

I am making a strange observation regarding the ptracers-pkg.
In my experiments I use a linear equation of state with sBeta=0, so 
that salinity is a passive tracer. In addition to that I use ptracers 
and kpp (and gchem with my private bgc-model). No surface forcing for 
ptracers or salinity.
I observe that, only when my vertical resolution is hight (25kmx25kmx6m 
near the surface) the passive tracer fields become very noisy, while 
the "passive tracer" salinity remains smooth. I use the same advection 
scheme for all quantities (2nd order centered, although I have used 
dst3fl, 33, for ptracers, but that's not better). With KPP the 
KappaPtr=KappaS, as far as I can see, so that the only difference 
should be the right hand side. I know, that my rhs for ptracers is well 
behaved, but I haven't tried turning it off, yet.

Is there any reason why ptracers should be advected, mixed differently, 
as salinity with sBeta=0?

Martin

Martin Losch // mailto:mlosch at awi-bremerhaven.de
Alfred-Wegener-Institut für Polar- und Meeresforschung
Postfach 120161, 27515 Bremerhaven, Germany
Tel./Fax: ++49(471)4831-1872
http://www.awi-bremerhaven.de/People/show?mlosch