[MITgcm-support] Zonal velocity bands

[Neil Swart]

Hi Jason,

If I check  advcfl_wvel_max, it remains low. I have also tried to  
rectify the problem by tapering the windstress near the boundaries,  
or setting it to zero. A strong tapering does help, but in general  
does not solve the problem. I will try and pursue this more.

(PID.TID 0011.0001) %MON advcfl_wvel_max              =    
9.5183183632057E-05

thanks,
Neil

-----------------------------------
Neil Swart
Climate Modelling Group
University of Victoria
Victoria, BC, Canada

http://climate.uvic.ca/

On 26-Mar-10, at 11:20 AM, Jason Goodman wrote:

> On Mar 26, 2010, at 1:57 PM, Neil Swart wrote:
>
>> I'm not sure I understand your comment on periodicity for the  
>> forcing.
>
>> tauMax=0.1;
>> x=((1:nx)-0.5)/(nx-1); % nx-1 accounts for a solid wall
>> y=((1:ny)-0.5)/(ny-1); % ny-1 accounts for a solid wall
>> [X,Y]=ndgrid(x,y);
>>
>> tau=tauMax*sin(1.2*pi*Y);
>
> With a nonzero zonal velocity at the southern boundary, you'll get  
> a northward Ekman flow at the south wall: by continuity, this can  
> only be balanced by a ferocious vertical upwelling.  I'm guessing  
> you're getting some sort of numerical instability as a result.
>
> Try checking the vertical advective CFL number in the monitor  
> output (advcfl_wvel_max).  If it's a large fraction of 1, you're in  
> trouble.
>
>
>
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