[MITgcm-support] initial W caused by bathymetry?

David Hebert david.hebert.ctr at nrlssc.navy.mil
Tue Jan 6 21:12:54 EST 2009

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 

Thanks for your help,


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