[MITgcm-support] Nonhydrostatic mode and Kinetic energy

[Jean-Michel Campin]

Hi Sergey,

Thanks for pointing to this problem. I don't think there is
a problem in the code, but the documentation would need to be fixed.
Note that the expression of KE diagnosed in the monitor:
 pkg/monitor/mon_ke.F
contains the W contribution.

The KE as computed in pkg/mom_common/mom_calc_ke.F is used
a) for the quadratic bottom drags: without the W contribution, KE scale
  like the vertical shear, so not sure W should be added.
b) in some Reynolds scaling for horizontal viscosity (pkg/mom_common/mom_calc_visc.F):
  all these viscosity calculations are using only the horizontal velocity,
  so it seems more consistent to keep using KE without W contribution.
c) in the vector-invariant momentum formulation:
  here it's clear that KE should not include the W contribution
  since the the vorticity part only deal with horizontal components of the velocity.

Cheers,
Jean-Michel

On Mon, Nov 10, 2014 at 11:16:39AM +0400, Fancer Lancer wrote:
> Hello MITgcm developers and users.
> 
> I've discovered an inconsistency between the User's manual and the code.
> There is a routine, which calculates KE at any k-level MOM_CALC_KE() it
> resides the pkg/mom_common/mom_calc_ke.F . The manual states, that in the
> nonhydrostatic mode it is supposed to be calculated as:
> KE = 0.5*(u^2 + v^2 + e_{nh} w^2),
> but there is no vertical velocity in the  MOM_CALC_KE() routine at all. On
> the first glance (I'm not completely sure) this mistake should not affect
> the bottom drag forces, since there is the impermeable condition on the
> bottom. But there may be some other modules where KE is used and where w is
> not zero.
> Could someone clarify whether I'm right or wrong?
> 
> Sincerely,
> -Sergey
> 
> -------------------------------------
> Sergey V. Semin
> Post graduate course student
> - Applied Mathematics and Informatics, Institute of Radio-electronics and
> IT,
> NNSTU n.a. R.E.Alekseev, Russia

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