[MITgcm-support] balancing the heat equation

Nicolas Wienders wienders at ocean.fsu.edu
Thu Sep 6 14:06:22 EDT 2007


First my apologies for posting yesterday on the list a message
that obviously should not have.

> Hi Allison,
> without checking details in the code I would suggest that you use  
> the diagnostics package for diagnosing the different contributions.  
> As far as I can see, the diagnostics are all available:
> dT/dt:
>       diagName  = 'TOTTTEND'
>       diagTitle = 'Tendency of Potential Temperature'
> uTx/vTy/wTz: 'ADVx/y/r_TH '
> KTxx/yy/zz: 'DFx/y/rE_TH ' (and 'DFrI_TH ' for the implicit part  
> which is relevant for KPP)
> Then there is the non-local term in KPP, which can be diagnosed  
> with 'KPPghat '; however that is not the contribution to diffusive  
> flux, and you'll have to alter the code a little to get that  
> contribution with the diagnostics package. Here's a hack that  
> abuses DFrE_TH for this purpose: In gad_calc_rhs.F find the calls  
> to KPP_TRANSPORT_T etc. They are within a #ifdef ALLOW_KPP/#endif  
> block. just before this there is a diagnostics call (#ifdef  
> ALLOW_DIAGNOSTICS/#endif). Just exchange the order of these two  
> blocks and DFrE_TH will give you the flux-contribution of the non- 
> local term (but the explicit diffusive flux will be overwritten and  
> not diagnosed, which is only OK, if you are using KPP without  
> A better solution is to add  a new diagnostic and insert it after  
> the calls to KPP_TRANSPORT_T etc).

Second, and following Allison's question, how should one write the  
heat equation
(using KPP and not gmredi) in order to reach a machine precision  
balance. We have
been trying for a while without any success.  We are mostly concerned  
by the non-local
term but might already be wrong upstream. So far we only have the  
volume balance

Thanks a lot.


Nicolas Wienders                            (850) 644-1987 (office)
Florida State University                              294-3542 (cell)
Oceanography - OSB415                          644-2581 (fax)
P.O. Box 3064320                      117 N. Woodward Avenue
Tallahassee, FL 32306-4320    wienders at ocean.fsu.edu

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