[MITgcm-support] Extracting the non-Ekman component of vertical velocity

[Martin Losch]

Hi Takaya,

the vertical velocity in the C-grid model is at the top of the k-th grid cell (see model documentation and header of GRID.h for details). The vertical velocity at the bottom of a water colum is alway zero (no flow througth the bottom). Therefore for a flat-bottom domain with no topography the vertical velocity at Nr+1 is always assumed to be zero. In fact, this layer Nr+1 does not exist, that why it cannot be included in output. I am not sure if I understand your question about Ekman and non-Ekman components. The model does not differentiate between different dynamical regime components.

Hope that helps,
Martin

> On 31. Jul 2018, at 04:27, Uchida Takaya <tu2140 at columbia.edu> wrote:
> 
> Dear MITgcm support.
> 
> I currently have the outputs for a flat-bottom zonally re-entrant channel model. Since it's a flat bottom, the vertical velocity at the bottom should be zero. 
> The issue I’m facing is that MITgcm only outputs the vertical velocity down until to the grid point right above the very bottom, which has relatively large root-mean square values (figure attached below for a snapshot of the vertical velocity).
> My current guess is that the vertical velocity goes to zero at the bottom in the calculation from Ekman contributions. Is there a simple and numerically consistent way to parse out the non-Ekman component of vertical velocity?
> 
> Thank you very much for your support in advance.
> 
> Best,
> Takaya
> ———————
> PhD Candidate
> Physical Oceanography
> Columbia University in the City of New York
> https://roxyboy.github.io/
> 
> <Screen Shot 2018-07-30 at 10.17.45 PM.png>
> 
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