[MITgcm-support] Temperature drift in tutorial ( tutorial_global_oce_latlon: Global Ocean Simulation at 4◦ Resolution).

[Martin Losch]

Hi Krishnakumar,

This behavior is expected: The tutorial_global_oce_latlon is forced by a hea flux that is globally balanced (should lead to no net temperature drift), AND a restoring term. This restoring term ( -(lev_sst.bin - theta)/tauThetaClimRelax ) causes the drift until the model has reached an equilibrium with this forcing (the same is true for salinity: fresh water flux plus restoring to sss). This can take very long, see e.g.
Gokhan Danabasoglu , Ocean Modelling 7 (2004) 323–341, A comparison of global ocean general circulation model solutions obtained with synchronous and accelerated integration methods
where the spin up takes up to 10,000 years. That's just the way it is.

If you want to get rid of the mean temperature trend then you have get rid of the restoring terms, but that will most likely give you a strange circulation.

Martin


On Mar 14, 2011, at 8:01 PM, Krishnakumar Rajagopalan wrote:

> Hi All,
> 
> 
> 
> We ran the tutorial (tutorial_global_oce_latlon) for a thousand years and find that there is a drift in the temperature.  See the attached figure which shows, for example,  the temperature at longitude=158deg and latitude= 2deg, for some depths;  the temperature at 3010m fails to reach a steady state even after 1000yrs. Although the annual integral of Qnet equals zero, the annual integral of heat flux flowing into the computational domain due the relaxation term is not. Could this be a reason for the drift in temperature? Is there any setting/method to reduce this (drift in temperature).  Our study also shows that the temperature drift persists even on a higher resolution grid.
> 
> 
> 
> Thanks in advance
> 
> 
> 
> Krishnakumar
> 
> 
> 
> (University of Hawaii at Manoa)
> 
> 
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