[MITgcm-support] non-hydrostatic momentum budget

[Andrea Cimatoribus]

One step ahead:

as hinted in http://mitgcm.org/sealion/online_documents/node38.html
I tried summing the nonhydrostatic pressure term:

Um_NHP = -(PHI_NH(i) - PHI_NH(i-1)) / DXC

The results definitely improve near the boundary, but I am still missing
something.

Best,
Andrea

Andrea Cimatoribus
postdoctoral researcher
EPFL ENAC IIE ECOL
https://people.epfl.ch/andrea.cimatoribus

On 06/07/17 17:30, Andrea Cimatoribus wrote:
> Dear all,
> I am trying to compute the budget of momentum in my non-hydrostatic 
> configuration. First of all, thanks to all those who contributed in the 
> past on this topic, it certainly saved me huge amounts of time and 
> head-scratching.
> 
> I put here the recipe from JMC for reference:
> [du/dt] = - gravity * ( ETAN(i) - ETAN(i-1) ) / DXC
>          + Um_dPHdx
>          + Um_Advec   (+ Um_Cori : but only if using CD-Scheme )
>          + Um_Diss    (+ Implicit vertical viscosity tendency)
>          + Um_Ext
>          + AB_gU
> 
> The problem:
> the recipe above works beautifully (relative error <<1e-3) in the 
> hydrostatic case, with only some issues near the boundary, I guess 
> because of my cheap ETA derivatives. However, in the nonhydrostatic 
> case, the above budget gives relative errors around 10% in many places 
> (10% of the "truth" diagnosed via TOTUTEND/TOTVTEND).
> 
> What term am I missing? Could it be that TOTUTEND does not have all the 
> terms in the NH case? I tried looking into mom_vecinv.F, but I could not 
> reach any conclusion. I also tried playing with ADVrE_Um/ADVrE_Vm fluxes 
> (treating it as the implicit vertical viscosity term), but that didn't 
> help either (I thought the vertical advection was missing).
> 
> Thank you for your insights,
> Andrea
> 
> 
> PS: I attach the data file and a figure for the curious ones, it shows 
> the relative error of the diagnosed acceleration (magnitude of vector) 
> with respect to the one directly produced via TOTUTEND/TOTVTEND. There 
> seems to be some correlation (not perfect, though) between the relative 
> error and the advective term.
> 
> 
> 
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