Noisy SST

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xavierC
Posts: 10
Joined: Thu Jul 16, 2009 5:17 pm
Location: Madeira University

Noisy SST

#1 Post by xavierC » Tue May 28, 2019 11:52 am

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
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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 390 times
Last edited by xavierC on Tue May 28, 2019 12:19 pm, edited 1 time in total.

c.drinkorn
Posts: 68
Joined: Thu Mar 08, 2018 2:47 am
Location: German Research Centre for Geosciences

Re: Noisy SST

#2 Post by c.drinkorn » Tue May 28, 2019 12:19 pm

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

xavierC
Posts: 10
Joined: Thu Jul 16, 2009 5:17 pm
Location: Madeira University

Re: Noisy SST

#3 Post by xavierC » Tue May 28, 2019 12:32 pm

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...

c.drinkorn
Posts: 68
Joined: Thu Mar 08, 2018 2:47 am
Location: German Research Centre for Geosciences

Re: Noisy SST

#4 Post by c.drinkorn » Tue May 28, 2019 1:39 pm

Then the only idea I have is to enable TS_MPDATA which will "force" the fields to be in 3d consistency...

jcwarner
Posts: 798
Joined: Wed Dec 31, 2003 6:16 pm
Location: USGS, USA

Re: Noisy SST

#5 Post by jcwarner » Tue May 28, 2019 2:52 pm

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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kate
Posts: 3678
Joined: Wed Jul 02, 2003 5:29 pm
Location: IMS/UAF, USA

Re: Noisy SST

#6 Post by kate » Tue May 28, 2019 4:07 pm

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.

c.drinkorn
Posts: 68
Joined: Thu Mar 08, 2018 2:47 am
Location: German Research Centre for Geosciences

Re: Noisy SST

#7 Post by c.drinkorn » Wed May 29, 2019 8:14 am

Code: Select all

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?

xavierC
Posts: 10
Joined: Thu Jul 16, 2009 5:17 pm
Location: Madeira University

Re: Noisy SST

#8 Post by xavierC » Wed May 29, 2019 2:31 pm

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.
Attachments
Capture d’écran 2019-05-29 à 09.24.40.png
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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 312 times

User avatar
kate
Posts: 3678
Joined: Wed Jul 02, 2003 5:29 pm
Location: IMS/UAF, USA

Re: Noisy SST

#9 Post by kate » Wed May 29, 2019 3:27 pm

c.drinkorn wrote:

Code: Select all

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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