[MITgcm-support] cosPower with GMRedi and Leith viscosity

[Naughten, Kaitlin A.]

To whom it may concern,

My name is Kaitlin Naughten and I have just started a postdoc at the British Antarctic Survey. I am setting up a Weddell Sea configuration of MITgcm, using an older configuration from a colleague as a starting point. The old configuration used version c62r which I have now updated to c67, so I expect many options and "best practices" have changed between these versions.

Right now I'm trying to make sure I'm doing something sensible with mixing. GMRedi and KPP are switched on, and the relevant namelist parameters are as follows:

viscAr=1.E-4
viscC2leith=3.0
viscC2leithD=3.0
diffKrT=1.E-4
diffKrS=1.E-4
cosPower=2.

>From old messages here, it looks like my choices of mixing schemes are reasonable. But I am confused about whether cosPower is needed. ISOTROPIC_COS_SCALING is defined in GAD_OPTIONS.h, but not in CPP_OPTIONS.h, so I understand cosPower only affects the tracers. But since GMRedi is on, is cosPower actually necessary and does it do anything? Furthermore, should I have cosPower scaling the momentum terms, or does the Leith parameterisation already scale by grid size? I've looked at some old messages and at the code but I can't quite figure it out.

If it matters, the grid is polar spherical, quarter-degree scaled by cos of latitude, and I can see some eddy activity resolved. Later we plan to increase resolution.

Many thanks,
Kaitlin Naughten
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