[MITgcm-devel] Hack to increase mixing near bottom/surface

[Martin Losch]

Hi Jean-Michel,

I am not sure if I can contribute  to this, but I can speculate about your question:

> I wonder if this large sensitivity of melt-rate when using SHELFICEuseGammaFrict=T
> is common ? or is it due to no-rotation ? or maybe there is something wrong in
> my wet-point averaging code (now cheked-in) ?

when using SHELFICEuseGammaFrict the melt rates become much more sensitive to the details of the flow regime. With constant exchange coefficients (SHELFICEuseGammaFrict=F), the heat flux/melt rate is determined by the temperature difference to the freezing point, i.e. the deeper, the more melting with the same potential temperature, and the warmer the temperature the more freezing, and it’s just a matter of where the warm water is brought into contact with the ice shelf bottom. With SHELFICEuseGammaFrict=T, the highest melt rates are found where the under-ice currents are larges (and uStar is largest). I assume that changing the vertical mixing with your “hack” is enough to substantially change the circulation and hence the strength of the boundary currents under the ice; or modifying uStar by averaging changes the actual strength of the exchange and hence the melting.

Am I stating the obvious?

M