[MITgcm-support] Lateral heat flux due to temperature restoring

[Josephine Anselin - BAS]

Hi Jean-Michel,

Thank you very much for your reply.

Regarding your point 1):
- I am not using z* (select_rStar = 0 in the model configurations)
- I am not using implicitDiffusion (implicitDiffusion = FALSE in the model configuration)
--> Do these settings change the way I should be computing the tendency due to diffusion term? (as opposed to following the approach described in the document I referenced in my original email?)

Regarding your point 2):
The temperature is restored using pkg/rbcs. 
Thank you for pointing out the 'forcing tendency' diagnostics, I had not yet looked at what these look like.

Also, I just noticed that I had made a typo in my script used to calculate the tendency due to advection term. With the correction, the residual (Residual = TOTTTEND/86400 - Adv_tend - Dif_tend) is now much smaller. But I am not sure if the use of TOTTTEND is appropriate here.
--> Given that the model configuration uses a non-linear free surface (nonlinFreeSurf=4), is it appropriate to use TOTTEND to estimate the total temperature tendency, or would it be more appropriate to evaluate this using ETAN?

Thank you,
Josephine



-----Original Message-----
From: MITgcm-support <mitgcm-support-bounces at mitgcm.org> On Behalf Of Jean-Michel Campin
Sent: 17 September 2024 19:36
To: mitgcm-support at mitgcm.org
Subject: Re: [MITgcm-support] Lateral heat flux due to temperature restoring

Hi Josephine,

I would like to know few other details about your set-up and configuration:
 1) are you using z* (i.e., select_rStar=1 or 2), and are you using implicitDiffusion=T ?
 2) and regarding this: 
> Temperature and salinity are restored at the open lateral boundaries.
   are you using pkg/rbcs or is it applied as part of the pkg/obcs "sponge" option ?
  In the first case (with pkg/rbcs), the tendency from the relaxation would be included
  inside the general (3-D) "forcing" tendency" diagnostics "gT_Forc ' and "gS_Forc ",
  but not if using pkg/obcs "sponge" option..

Cheers,
Jean-Michel

On Tue, Sep 17, 2024 at 04:14:38PM +0000, Josephine Anselin - BAS wrote:
> Hi everyone,
> 
> I am evaluating the heat budget in a 3D domain with nx=640 grid points in the x-direction; ny=1200 grid points in the y-direction and nz=150 grid points in the z direction. The domain includes open ocean, ice shelf and grounded ice cells. Temperature and salinity are restored at the open lateral boundaries.
> 
> The following parameter settings are used:
> implicitFreeSurface=.TRUE.
> nonlinFreeSurf=4.
> useRealFreshWaterFlux=.FALSE.
> 
> To begin with, I am trying to close the budget for the cells away from the ice shelf-ocean interface and away from the ocean surface. I was assuming that for these cells, the heat budget should be:
> TOTTEND/86400 = Adv_tend + Dif_tend,
> with Adv_tend and Dif_tend calculated as per page 3 in this document: 
> https://mitgcm.org/download/daily_snapshot/MITgcm/doc/Heat_Salt_Budget
> _MITgcm.pdf (KPPg_TH and oceQsw are zero in the model configuration).
> 
> However, the heat budget does not close using this calculation.
> I would like to investigate the potential impact of the lateral heat flux due to temperature restoring to check if this might be causing the large residual.
> Is there a diagnostics analogous to TRELAX but for lateral heat flux instead of surface heat flux?
> If not, does anyone have any suggestions on how this could be calculated using built-in diagnostics?
> 
> Thank you
> Josephine
> 
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