[MITgcm-support] definition of UVEL

[Martin Losch]

Zhaomin,

although I like Ryan's comment about IPCC models, it is fair to say, that the ACC transport depends  mostly on bathymetry, stratification and wind (the latter setting the stratification in the long run). If you want to debug your configuration (assuming a "simple" lat-lon grid and that your bathymetry is not completely strange), you can 

1. run the model for some time (1year) without wind forcing: the stratification should lead to a reasonable transport through Drake Passage. In longer integrations the stratification will erode, if not maintained by wind or buoyancy forcing. and the ACC will weaken with time.
2. turn on (periodic?) wind forcing. Now the ACC should quasi-equilbrate quickly (wiithin a year) and then it will probably drift a little, depending on the details of your forcing. Again, the wind and buoyancy forcing maintain the stratification, but because things are not perfect, your specific forcing may lead to a slightly different stratification, hence a different ACC transport.
3. start the model from flat hydrography (\nabla_h \rho = 0) have the wind spin-up the stratification. This will take a little longer to get a reasonable ACC (10-100 years)

If 1 does not work, but 3 does, then the initial conditions are unrealistic.
If 1 works, but 2 doesn't, then the wind forcing is most likely wrong. 

Martin


On Apr 2, 2011, at 1:20 AM, Ryan Abernathey wrote:

> Zhaomin,
> 
> The problem is not so serious. Several IPCC models are known to have UVEL negative in the ACC region as well.
> 
> Best,
> Ryan
> 
> On Apr 1, 2011, at 12:31 PM, Wang, Zhaomin wrote:
> 
>> Can somebody let me know if UVEL is defined as total zonal velocity or something else? We found that UVEL is too small or even negative in the ACC regions in our output. If UVEL is total zonal velocity, we need to check if we made a mistake in our run.
>> 
>> Zhaomin
>> 
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