[MITgcm-support] funky ice dynamics in doubly periodic domain

[Dimitris Menemenlis]

Martin, the domain is doubly periodic.  There are no lateral boundaries.

Initially I thought it was the mass of the ice itself that was doing the
integration/smoothing/low-pass filtering of the wind forcing function.
But back of the envelope calculation for 3-m ice, .1 N/m^2 surface
stress gives acceleration of 3 m/s/day!  So it has to be the bottom
ice stress that’s keeping the ice from moving much in the winter.

I would love to see a time series of velocity at different depths
below the ice.  Or even better a computation of stress (momentum transfer)
from ice to ocean — do we have a canned diagnostic for that?  I forget.

Dimitris Menemenlis

> On Feb 23, 2016, at 2:15 AM, Martin Losch <Martin.Losch at awi.de> wrote:
> 
> if you use a spatially homogeneous forcing fields (the same value for all grid points) that just varies in time, I am not surprised, especially if the wind blows only along the channel (is that the case?). In summer the ice is mobile because AREA<1. Already at AREA<.90 there is hardly any resistence in the ice with default paramerers because of the  exp-function term in the strength parameterisation. As AREA->1 ice strength increases and it will be very hard to deform ice by convergent motion. With a solid ice cover and no divergence in the wind field I don’t see any reason, why the ice should move at all, unless you use free slip boundary conditions and there is some mean drift effect (btw, 10cm/s or even 5cm/s is not very small in that case). 
> If you want to see something “interesting” in winter you need to introduce some sort of divergence into the ice motion, e.g. by introducing divergent wind forcing, or add some obstacle in the channel (see verification/offline_exf_seaice for an example). But still, with 100% ice cover and fairly thick ice there is going to be very little ice motion. That’s the whole point of the set of parameterisations, that we call a sea ice model.