[MITgcm-support] initial W caused by bathymetry?

[Martin Losch]

David,

what is the scale of the w-values? The only thing I can think of is  
that this is the round-off error showing up. This would not be  
visible with a non-uniform u-field, because other ("real") effects  
would dominate.

Martin
On 7 Jan 2009, at 03:12, David Hebert wrote:

> Hi Everyone,
>
> I would like to conduct a 3D, nonhydrostatic simulation with a  
> barotropic flow over a seamount. In the past I have typically  
> started these simulation with a U velocity throughout the domian.  
> In this case, U=10cm/s. Since U=10cm/s everywhere (and V=0) at t=0,  
> I would expect continuity to be satisified and W=0. However, I get  
> several vertical "stripes" for W at t=0 (see attached vertical  
> cross-sections for U,W at t=0).  These "stripes" seem to be caused  
> because the model is using areas where there is bathymetry to  
> compute continuity. i.e., where there is land, U=0, and the  
> adjacent point U=10cm/s, resulting in a nonzero value of du/dx.  
> Furthermore, since du/dx is zero above the bathymetry, the induced  
> W is manifested vertically.
>
> My question is has anyone come across this issue where bathymetry  
> seems to cause velocity gradients? How do I get around it? I should  
> note I see similar stripes in W when I initialize U and V from a  
> larger domain simulation.
>
> Thanks for your help,
>
> David
>
> <Ut0.png>
> <Wt0.png>
> <Ut0.png><Wt0.png>
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