[Mitgcm-support] Re: Variable Az in MITgcm

[mitgcm-support at dev.mitgcm.org]

Petter,

You are right in all aspects of your message; calc_viscosity.F was
created for this exact purpose. Be careful about lateral staggering
of variables when calculating the sqrt(uzz+vzz) term; there is
some four point averaging needed.

Rgds,

Alistair.

> Petter Stenström wrote:
> 
> Alistair,
> 
> I need to use a variable vertical viscosity coefficient calculated from local
> shear and stratification according to:
> 
> Az=const.*sqrt( (du/dz)^2 + (dv/dz)^2 - g/rho0*drho/dz )
> 
> Browsing the code, I concluded that it should be fairly easy to do, which
> makes me suspicious... Can I just check with you that I haven't missed
> anything important?
> 
> It seems that I could just set viscAr to a small background value and then add
> a variable part in the sbrt calc_viscosity, based on local values of du/dz,
> dv/dz and drho/dz (based on the model variables uVel, vVel, rholoc and
> recip_drF).
> 
> It further seems that even though vertical dissipation is given in the
> documentation as:
> 
> Az*(d2u/dz2)
> 
> it is actually calculated in the model as:
> 
> d/dz(Az*du/dz)
> 
> i.e. Av doesn't necessarily have to be a constant. Is that correct?
> 
> Regards,
> 
> Petter Stenström
> Dept of Land and Water Res Eng
> Royal Institute of Technology
> SE-100 44 Stockholm
> Phone: +46 8 7908657
> Email: petters at kth.se