[MITgcm-support] Bulk forcing and partial cells

[Martin Losch]

Hi Oceane,

this typically happens when (surface) ocean points are nearly isolated, i.e. only have only one grid cell face in common with the rest of the domain. Then there is no advection possible and only diffusion can remove anomalous values (and with stable, diffusive advection schemes, there’s often no explicit diffusion turned on). The surface forcing keeps adding/removing freshwater, and with a linear free surface, this is done by some sort of virtual salt flux, so that you keep increasing/decreaing the salinity without balancing this input by lateral fluxes of salinity. The partial cells don’t really make a difference, except that the cell volume may be even smaller so that you can fill up your smaller cell with salt even faster.

To solve this, I’d try the non-linear free surface (because the added freshwater will change not change the salt content, but the surface height which is quickly compensated by fast waves), or remove these individual points from the bathymetry, or add additional points to allow flow.

Martin

> On 15. Nov 2019, at 06:39, Richet, Oceane (O&A, Hobart) <Oceane.Richet at csiro.au> wrote:
> 
> Hello everyone,
> 
> I am using the bulk formula package to force my regional model. My simulation runs but I have few crazy values for the salinity (from -200 to 90 psu). All these points are coastal points and correspond to partial cells. Do you know if partial cells are taken into account in the calculation of the freshwater flux from the bulk formula? It does not look to be the case but I can be wrong. And do you have an idea how to fix this problem?
> 
> Thank you
> 
> Océane Richet
> CSHOR Postdoctoral Fellow 
> CSIRO, Hobart, Australia
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