[MITgcm-support] vertical momentum tendency

Tue May 24 05:40:48 EDT 2022

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 (钱钰坤)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

------------------ 原始邮件 ------------------
发件人: "Martin Losch"<Martin.Losch at awi.de>;
发送时间: 2022年5月23日(星期一) 晚上10:33
收件人: "MITgcm-support"<mitgcm-support at mitgcm.org>; 

主题: 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, 钱钰坤 <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 (钱钰坤)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

------------------ 原始邮件 ------------------
发件人: "Matthew Mazloff"<mmazloff at ucsd.edu>;
发送时间: 2022年5月18日(星期三) 上午9:47
收件人: "MITgcm-support"<mitgcm-support at mitgcm.org>; 

主题: 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, 钱钰坤 <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 (钱钰坤)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

------------------ 原始邮件 ------------------
发件人: "Haoran Xu"<xu1jian2wei3 at 163.com>;
发送时间: 2022年5月17日(星期二) 晚上7:40
收件人: "MITgcm-support"<mitgcm-support at mitgcm.org>; 

主题: 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, "钱钰坤" <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 (钱钰坤)
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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