[MITgcm-support] vertical momentum tendency

Tue May 24 12:39:44 EDT 2022

Hi Yu-Kun,

Regarding diagnostic TOTVTEND, it's filled up with the same variable "vVel"
two times in diagnostics_fill_state.F,
the first time at the begining of the time step, with a negative sign (tmpFac = -86400/detaTMom), 
and the second time at the end of the time step, with a positive sign (tmpFac = +86400/delaTMom).
This way we get the difference of vVel between the end of time-step and begining of time-step.
Note that the second time it's filled up we don't increment the counter (the 7th argument is
-1 instead of +1).

I have the impression that if you follow the same double filling for TOTWTEND it 
should work.

Cheers,
Jean-Michel

On Tue, May 24, 2022 at 05:40:48PM +0800, ?????? wrote:
> Hi Martin,
> 
> 
> Thank you for your suggestion.  I follow your method and integrate the divergence tendency
> to get W-tendency, with the output at dt frequency (so that the true tendency can be verified).
> This is indeed a way to get TOTWTEND but the tendency computed as (W[t+1]-W[t])/dt seems
> to have a dt/2 offset relative to the divergence way.  So the difference cannot be minimized
> up to machine accuracy.
> 
> Since I need to close the energy budget to machine accuracy, I may need the online TOTWTEND
> and decide to add a user-defined diagnostic for this.  It is somewhat confusing that the following
> three lines (see here):
>     CALL DIAGNOSTICS_SCALE_FILL( uVel, tmpFac, 1, 'TOTUTEND',0,Nr,0,1,1,myThid )
>    CALL DIAGNOSTICS_SCALE_FILL( vVel, tmpFac, 1, 'TOTVTEND',0,Nr,0,1,1,myThid )
>    CALL DIAGNOSTICS_SCALE_FILL( wVel, tmpFac, 1, 'TOTWTEND',0,Nr,0,1,1,myThid )
> do not give similar results.  The first two lines indeed fill TOTUTEND/TOTVTEND with tendency of
> 
> u/v, whereas the third line fill TOTWTEND with vertical velocity itself (magnified by 86400).
> 
> 
> Can somebody help me resolve this?
> 
> 
>   Best regards 
>  
> -----------------------------------------
> Yu-Kun Qian (??????)South China Sea Institute of Oceanology
> Sun Yat-sen University
> Xingang West Road, Haizhu District
> Guangzhou, P.R. China
> Email: qianyukun at scsio.ac.cn, qianyk at mail3.sysu.edu.cn
>    
>  
> 
>  
>  
>  
> ------------------ ???????? ------------------
> ??????: "Martin Losch"<Martin.Losch at awi.de>;
> ????????: 2022??5??23??(??????) ????10:33
> ??????: "MITgcm-support"<mitgcm-support at mitgcm.org>; 
> 
> ????: Re: [MITgcm-support] vertical momentum tendency
> 
>  
> 
> I am not sure, if this is a useful comment, but even in a non-hydrostatic simulation, the flow field is non-divergent and you coiuld diagnose wVel from the vertical integral of the horizontal divergence (in fact, the model does this in a non-hydrostatic simulation, too). In the same way, and since the operations are linear you coud diagnose dw/t from - \nabla_h du/dt, couldn??t you?
> 
> Martin
> 
> On 23. May 2022, at 15:36, ?????? <qianyk at mail3.sysu.edu.cn> wrote:
> 
> Hi,
> 
> 
> I might find a workaround to get instantaneous TOTWTEND (not time-mean one)
> by adding the following lines:
>   CALL DIAGNOSTICS_SCALE_FILL( wVel, tmpFac, 1, 'TOTWTEND',0,Nr,0,1,1,myThid )
> to diagnostics_fill_state.F file, following TOTUTEND and TOTVTEND  (see here).  And
> also add a call to 
>   CALL DIAGNOSTICS_ADDTOLIST()
> at diagnostics_main_init.F (see here).
> 
> 
> Then I re-compile the model and run it well.  However, the tendency of w TOTWTEND
> seems to be much larger than expected in my case:
> <7239677D at 602E0261.C58D8B62.png>
> 
> 
> I am not sure DIAGNOSTICS_SCALE_FILL really do the time-differencing.  Is this
> the right way to get TOTWTEND?  Why it looks so large in magnitude?
> 
> 
> 
>   Best regards 
>  
> -----------------------------------------
> Yu-Kun Qian (??????)South China Sea Institute of Oceanology
> Sun Yat-sen University
> Xingang West Road, Haizhu District
> Guangzhou, P.R. China
> Email: qianyukun at scsio.ac.cn, qianyk at mail3.sysu.edu.cn
>    
> 
> 
>  
> ------------------ ???????? ------------------
> ??????: "Matthew Mazloff"<mmazloff at ucsd.edu>;
> ????????: 2022??5??18??(??????) ????9:47
> ??????: "MITgcm-support"<mitgcm-support at mitgcm.org>; 
> 
> ????: Re: [MITgcm-support] vertical momentum tendency
> 
>  
> 
> Hi Haoron
> 
> Dump snapshots at the interval you need to get dW/dt.
> 
> 
> For example daily tendency would be derived from 
>    frequency(1) = -86400.0,
>    timePhase(1) = 0.0,
>    fields(1,1) = 'WVEL    ',
>    filename(1) = ??WvelSnap??,
> 
> 
> 
> 
> Matt
> 
> 
> On May 17, 2022, at 5:47 PM, ?????? <qianyk at mail3.sysu.edu.cn> wrote:
> 
> Hi Haoran,
> 
> 
> Thank you for your help.  But I don't really know how these two diagnostics
> could help in deriving the tendency of w (unit of acceleration).
> 
> 
> My understanding is that these two diagnostics are useful in calculating the
> eddy momentum flux when the output is time-average <> one.  For example,
> <w'u'> = <wu> - <w><u>
> If we output monthly mean wu, w, and u, we can get eddy flux <w'u'> for this
> month.
> 
> 
> 
>   Best regards 
>  
> -----------------------------------------
> Yu-Kun Qian (??????)South China Sea Institute of Oceanology
> Sun Yat-sen University
> Xingang West Road, Haizhu District
> Guangzhou, P.R. China
> Email: qianyukun at scsio.ac.cn, qianyk at mail3.sysu.edu.cn
>    
>  
> 
>  
>  
>  
> ------------------ ???????? ------------------
> ??????: "Haoran Xu"<xu1jian2wei3 at 163.com>;
> ????????: 2022??5??17??(??????) ????7:40
> ??????: "MITgcm-support"<mitgcm-support at mitgcm.org>; 
> 
> ????: Re: [MITgcm-support] vertical momentum tendency
> 
>  
> 
> Hi??
>  If I understand correctly,these two diagnostics could help.
> 
> 
> 
> 
> WU_VEL  |WU      LR|m.m/s^2         |Vertical Transport of Zonal Momentum WV_VEL  |WV      LR|m.m/s^2         |Vertical Transport of Meridional Momentum
> 
> 
>  Haoran Xu.
> 
> 
> 
> 
> At 2022-05-17 18:30:48, "??????" <qianyk at mail3.sysu.edu.cn> wrote:
> Hi all,
> 
> 
> Just a quick question.  Why there is no tendency of vertical momentum,
> like TOTWTEND, in the diagnostics even the non-hydrostatic option is
> turned on?
> 
> 
> To close the energy budget, I guess we need this diagnostic.  Is there any
> workaround to obtain it if there is no TOTWTEND?
> 
> 
> 
> 
>  Best regards.
>  
> ---------------------------
> Yu-Kun Qian (??????)
> South China Sea Institute of Oceanology
> 
> Sun Yat-sen University 
> Xingang West Road, Haizhu District 
> Guangzhou, P.R. China
> Email: qianyk at mail3.sysu.edu.cn      
> 
> 
>  
> 
> 
> 
> 
>  
> 
> 
> 
> 
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