[MITgcm-support] RBCS relaxation time scale limits

[Dhruv Balwada]

Thanks Martin. Yes, it makes sense when you put it that way.

Dhruv

On Sun, Mar 11, 2018 at 2:32 PM, Martin Losch <Martin.Losch at awi.de> wrote:

> Hi Dhruv,
>
> if you ignore other sources for your tracer, you’ll have from discretizing
> d Tracer/ dt  = 1/tauRelax * ( Tracer_r - Tracer ) in time (it’s more
> complicated, but just conceptually):
> Tracer(n+1) = Tracer(n) + dt/tauRelax * ( Tracer_r - Tracer(n) )
> for tauRelax = deltaT, this means Tracer(n+1) = Tracer_r, ie you replace
> your tracer with the restoring value. A shorter restoring time scale
> doesn’t make too much sense to me. And if you use the above logic for
> tauRelax << deltaT then (deltaT/tauRelax>>1) and I am not quite sure what
> you would be getting. Maybe your advection scheme limits the effect of the
> restoring after you get funny values from deltaT/tauRelax >> 1
>
> I suggest that you don’t use tauRelax<deltaT.
>
> Martin
>
> > On 10. Mar 2018, at 21:27, Dhruv Balwada <db194 at nyu.edu> wrote:
> >
> > Hello,
> >
> > I am trying to do some surface tracer restoration experiments with
> relaxation time scales that are very fast (1s), extreme limit. This number
> is smaller than the time step in my experiment. I use the RBCS package for
> this. I am noticing that if the restoration time scale is smaller than the
> time step, then no tracer enters the domain. However, things work fine/as
> expected if the restoration time scale is larger than or equal to the time
> step. Is there some reason why this is the case? The restoration time scale
> seems to enter as a constant, not sure why it is tied to the numerics.
> >
> > Thanks,
> > Dhruv
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