Ocean Modeling Discussion

ROMS/TOMS

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 Post subject: Noisy SST
PostPosted: Tue May 28, 2019 11:52 am 
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Joined: Thu Jul 16, 2009 5:17 pm
Posts: 10
Location: Madeira University
Hello,
I am doing some ROMS modelling and although it goes quite smooth, i have some noise on the temperature field, mainly at the surface, as you can see on the figure attached.

I am using
#define UV_ADV
#define TS_U3ADV_SPLIT
advections schemes (but i have tried others without any success)

and i have been playing around with viscosity and difusivity.
/*Horizontal Mixing */
#define TS_DIF4
#define TS_DIF2
#define UV_VIS2
/*Vertical Mixing*/
#define MIX_GEO_TS
#define MIX_GEO_UV
#define LMD_MIXING
#define LMD_BKPP
#define LMD_CONVEC
#define LMD_RIMIX
#define LMD_SKPP
#undef LIMIT_VDIFF
#undef LIMIT_VVISC

The model is stable and all other field are (or at least seem) smooth.

Would you have any idea of what i should do to resolve this issu and get smooth temperature ?

I forgot to mentionne that my time step is 100s and horizontal resolution 2.5km. Although i think it already too small i tried to reduce it, but once again without ay success .

Thanks in advance
Xavier


Attachments:
Capture d’écran 2019-05-28 à 14.19.27.png
Capture d’écran 2019-05-28 à 14.19.27.png [ 34.09 KiB | Viewed 293 times ]
Capture d’écran 2019-05-28 à 13.42.31.png
Capture d’écran 2019-05-28 à 13.42.31.png [ 40.46 KiB | Viewed 297 times ]


Last edited by xavierC on Tue May 28, 2019 12:19 pm, edited 1 time in total.
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 Post subject: Re: Noisy SST
PostPosted: Tue May 28, 2019 12:19 pm 
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Joined: Thu Mar 08, 2018 2:47 am
Posts: 68
Location: German Research Centre for Geosciences
Hi Xavier,

I switched from MIX_GEO_TS to MIX_S_TS in order to solve a similar problem at the bottom. Maybe it also helps you. :)

//Cate


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 Post subject: Re: Noisy SST
PostPosted: Tue May 28, 2019 12:32 pm 
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Joined: Thu Jul 16, 2009 5:17 pm
Posts: 10
Location: Madeira University
c.drinkorn wrote:
Hi Xavier,

I switched from MIX_GEO_TS to MIX_S_TS in order to solve a similar problem at the bottom. Maybe it also helps you. :)

//Cate


Thanks a lot for your answer Cate. I just made a try, but no sucess once again...


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 Post subject: Re: Noisy SST
PostPosted: Tue May 28, 2019 1:39 pm 
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Joined: Thu Mar 08, 2018 2:47 am
Posts: 68
Location: German Research Centre for Geosciences
Then the only idea I have is to enable TS_MPDATA which will "force" the fields to be in 3d consistency...


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 Post subject: Re: Noisy SST
PostPosted: Tue May 28, 2019 2:52 pm 
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Joined: Wed Dec 31, 2003 6:16 pm
Posts: 786
Location: USGS, USA
do the atm forcing fields look smooth ?
you could try mixing from my25 or gls and then activate N2S2_HORAVG.

-j


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 Post subject: Re: Noisy SST
PostPosted: Tue May 28, 2019 4:07 pm 
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Joined: Wed Jul 02, 2003 5:29 pm
Posts: 3633
Location: IMS/UAF, USA
The equivalent horizontal smoothing for LMD is LMD_SHAPIRO, to horizontally filter the mixed layer depth. I've heard from some other colleagues that they too need to smooth the mixed layer depth to avoid that sort of noise.

As for MIX_S_TS, it's a really bad idea over a sloping bottom and can lead to unphysical cross-isopycnal mixing.


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 Post subject: Re: Noisy SST
PostPosted: Wed May 29, 2019 8:14 am 
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Joined: Thu Mar 08, 2018 2:47 am
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Location: German Research Centre for Geosciences
Code:
As for MIX_S_TS, it's a really bad idea over a sloping bottom and can lead to unphysical cross-isopycnal mixing.

I hear you! But there was no way to solve the issue of punctual alternating high/low temperatures at the slope when mixing along z-planes which would even cause the model to blow up. The model doesn't "know" the sigma levels are aligned to the slope. It just detects strong gradients between adjacent cells and calculates way too high advection velocities leading to a sort of snowball effect, I think. How can this be solved otherwise?


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 Post subject: Re: Noisy SST
PostPosted: Wed May 29, 2019 2:31 pm 
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Joined: Thu Jul 16, 2009 5:17 pm
Posts: 10
Location: Madeira University
Hello,
thanks for your answsers, still have to try GLS or MY2.5, but I managed to try the "easy one" suggested by kate and i got a strong improvments of my solution. With some presistent noise only very near coast.


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Capture d’écran 2019-05-29 à 09.24.40.png
Capture d’écran 2019-05-29 à 09.24.40.png [ 16.09 KiB | Viewed 219 times ]
Capture d’écran 2019-05-29 à 09.23.16.png
Capture d’écran 2019-05-29 à 09.23.16.png [ 14.52 KiB | Viewed 219 times ]
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 Post subject: Re: Noisy SST
PostPosted: Wed May 29, 2019 3:27 pm 
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Joined: Wed Jul 02, 2003 5:29 pm
Posts: 3633
Location: IMS/UAF, USA
c.drinkorn wrote:
Code:
As for MIX_S_TS, it's a really bad idea over a sloping bottom and can lead to unphysical cross-isopycnal mixing.

I hear you! But there was no way to solve the issue of punctual alternating high/low temperatures at the slope when mixing along z-planes which would even cause the model to blow up. The model doesn't "know" the sigma levels are aligned to the slope. It just detects strong gradients between adjacent cells and calculates way too high advection velocities leading to a sort of snowball effect, I think. How can this be solved otherwise?

Maybe it depends on your priorities - what are the time and space scales you'd like to do right? Can you get a smooth enough result with the third-order advection and no diffusivity? Do you need the split advection scheme which may or may not be working well enough in the ROMS you are using? Do you need a different ROMS or another model entirely? Or can you live with what your ROMS is giving you?


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