[MITgcm-support] Abnormal high and low temperature in model

[Martin Losch]

Hi Yinghui He,

are the extreme temperatures associated with "holes" in the topography, i.e. grid points the have only one connection to the rest of the domain (i.e. upwards)? Or maybe the hFacC's are particularly small? You have a hFacMin of 0.05 (5%) or 10m, so you might get very thin layers. For the latter case try increasing hFacMin to 0.1 or even 0.3. For the former case: z-level models can handle "steep" and otherwise pathological topography, but it's always better to have a fairly smooth bottom.

In the end these extreme values are probably the consequence of overshoots in the advection scheme. You can reduce these by use more sophisticated schemes. I usually use the 3rd order DST with flux limiter
tempAdvection = 33,
saltAdvection = 33,
staggerTimeStep = .true. ! important for the so-called multidimensional schemes to which 33 belongs
With this scheme you can reduce the explicit horizontal diffusion (in theory to 0, because this scheme is "unconditionally" stable). I would use only gmredi for (explicit) horizontal mixing.

Hope that this helps,

Martin


On Jul 8, 2010, at 7:11 PM, 何映晖 wrote:

> Hi,
>  
> I’m running a global ocean model with variable grid-space. Yearly mean Trenberth wind stress is used to drive the ocean circulation. And surface temperature and salinity restoring boundary conditions are set.
> Though the model does not blow up after several years’ runs, some points with abnormal high or low temperature are found from the model, whereas there are no points of abnormal velocity near those abnormal temperature points. And I find those abnormal temperature points mainly emerge at the bottom layer. So I wonder why this problem occurred. Does the problem stem from bottom friction? Or because of the wrong value of mixing parameter set? How can I deal with these problems?
> The "data" file is in attachment. And some figures of these abnormal points at Japan Sea are also attached. Figure 1
> Fig. 1 illuminates temperatures at 22th layers, middle depth of 2840 meters. max temperature is up to 49.08℃, and minimum of -13.37℃. Fig. 2 shows the abnormal maximum salinity of 57.67 ppt corresponding to the abnormal point of max temperature. Fig. 3 shows the velocity at the same layer.
> Any suggestion to me will be deeply appreciated.
>  
> Best regards,
> Yinghui He
> 
> 
> -- 
> Yinghui He
> South China Sea Institute of Oceanology
> Chinese Academy of Sciences
> <data><Fig.1.jpg><Fig.2.jpg><Fig.3.jpg>_______________________________________________
> MITgcm-support mailing list
> MITgcm-support at mitgcm.org
> http://mitgcm.org/mailman/listinfo/mitgcm-support