SWMT shifts to lighter densities in MOM6-01

[schmidt-christina]

I calculated the SWMT in six different 1/10th MOM6 configurations:

• panant-01-zstar-v13: 1/10th panantarctic zstar run with ACCESS-OM2-01 year 200 IC + BF
• panant-01-hycom1-v13: 1/10th panantarctic hybrid run with ACCESS-OM2-01 year 200 IC + BF
• panant-01-zstar-ACCESSyr2: 1/10th panantarctic zstar run with ACCESS-OM2-01 year 2 IC + BF
• global-01-v1: 1/10th global zstar run (version 1) with ACCESS-OM2-01 year 200 IC
• global-01-v2: 1/10th global zstar run (version 2) with ACCESS-OM2-01 year 2 IC
• global-01-v3: 1/10th global hybrid run (version 3) with ACCESS-OM2-01 year 2 IC

The peak of the mean (1996-2000) SWMT in each of the 4 formation regions occurs at different densities with runs that start from year 200 of ACCESS-OM2-01 being denser (blue, orange, red line) and runs starting from year 2 of ACCESS-OM2-01 (i.e. close to WOA observations) being lighter. This is especially visible in the Weddell Sea.

The peak of the SWMT shifts to lighter densities each year in the runs that start from ACCESS-OM2-01 year 2 in all regions and especially in the Ross Sea.

In runs starting from ACCESS-OM2-01 year 200 the density of the peak SWMT isn't shifting to lighter densities as much and also slower (note that the 2nd Plot with panant-01-zstar-v13 includes 46 years more)

A timeries of the SWMT for a density at a mean (1991-2012) transport of 70% of the maximum transport (orange line) for panant-01-zstar-ACCESSyr2 shows that after 10 years the SWMT dropped below 0.5 Sv from around 2 Sv in the Weddell/Ross Seas.

I didn't see a difference between vertical coordinates, or whether it was global or panantarctic.
Plots for all of the runs are here: https://github.com/schmidt-christina/mom6_comparison/blob/main/SWMT_Plots.ipynb

[schmidt-christina]

We were wondering whether that had something to do with the initial stratification, so I looked at bottom T/S/rho and compared panant-01-zstar-v13 and panant-01-zstar-ACCESSyr2.

All plots and more detailed text are here: https://github.com/schmidt-christina/mom6_comparison/blob/main/Shelf_properties_Plots.ipynb

Initial temperatures don't differ much between panant-01-zstar-v13 and panant-01-zstar-ACCESSyr2 in the DSW formation regions, but it's up to 2°C warmer in the Amundsen/Bellingshausen Sea (not shown here).

Salinity: The initial conditions in the Weddell Sea are fresher (up to 0.2 psu) in panant-01-zstar-v13 compared to panant-01-zstar-ACCESSyr2. But this reverses with panant-01-zstar-v13 being saltier everywhere on the shelf after 10 years. The Weddell Sea gets saltier in panant-01-zstar-v13 and fresher in panant-01-zstar-ACCESS-yr2. The Amundsen Sea gets saltier and the Ross Sea fresher in both runs, but the magnitude of the freshening is slightly stronger in panant-01-zstar-ACCESSyr2, so that panant-01-zstar-v13 is still saltier.

Overall, it’s getting lighter everywhere on the Antarctic shelf in panant-01-zstar-ACCESS-yr2, especially in the Ross Sea.

Horizontal mean density profiles in the Weddell and Ross Sea have mostly the same shape in both runs, panant-01-zstar-ACCESS-yr2 is often lighter (with a constant offset over the whole water column compared to panant-01-zstar-v13). But it is not necessarily like that from the start, it often gets lighter over time as the SWMT shifts to lighter densities.

[adele-morrison]

Amazing analysis, thanks @schmidt-christina! Rather unexpected, because we have the same atmospheric forcing, same vertical grid and same horizontal resolution / bathymetry as ACCESS-OM2-01.

@AndyHoggANU suggested we could try playing around with the boundary layer vertical mixing schemes. I'll try to get some panan-01 test cases going today with different mixing schemes / parameters.

[AndyHoggANU]

Yeah, I agree this is a very nice analysis. I'm also very interested in seeing what we get out of the 1/20° case.
@schmidt-christina - if you have time to look at your current 1/20° simulation before our Monday morning meeting that would be helpful!

[schmidt-christina]

I have 5 years of the 1/20th run now. So far it doesn't look too bad, there is certainly not the same shift that I can see already in the first 5 years in the 1/10th run with same IC + BC etc. But as I only have five years yet, I would still be a bit cautious. Also the SWMT is quite weak in the Weddell Sea.

Plot below is the panant-01-zstar-ACCESS-yr2 with the shift visible already in the first 5 years for comparison:

[adele-morrison]

That’s good news! Did you decide at the meeting today to run longer? If so, has anyone checked what the density binning on vmo and umo is like? Might be good to double check the diagnostic list, so we don’t have to rerun 10 years (perhaps you already did this at the meeting today). Do we have x and y heat flux diagnostics switched on too?

…

On Mon, Apr 17, 2023 at 8:36 AM, Christina Schmidt ***@***.***> wrote: I have 5 years of the 1/20th run now. So far it doesn't look too bad, there is certainly not the same shift that I can see already in the first 5 years in the 1/10th run with same IC + BC etc. But as I only have five years yet, I would still be a bit cautious. Also the SWMT is quite weak in the Weddell Sea. [image: image] <https://user-images.githubusercontent.com/38216156/232346051-52918744-5362-497a-b61b-ed8c96901109.png> Plot below is the panant-01-zstar-ACCESS-yr2 with the shift visible already in the first 5 years for comparison: [image: image] <https://user-images.githubusercontent.com/38216156/232346063-d7b7dc9c-d4ad-463c-85ba-6cdeb1f76011.png> — Reply to this email directly, view it on GitHub <#40 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/ACA44UZCFUHRWX3DV3FSQ5TXBRYABANCNFSM6AAAAAAW4S7JMY> . You are receiving this because you commented.Message ID: ***@***.***>

[schmidt-christina]

Yes, we decided to run another 5 years and it's running atm. We briefly looked at the density binning, but decided that I would look at it in more detail. So maybe I can look at it first thing tomorrow morning and pause the run in the meantime?

What do you mean by "x and y heat flux diagnostics"?

[adele-morrison]

I wouldn't bother pausing, just keep running and see if you can check the density binning as soon as you can. Zonal and meridional heat fluxes, I'm not sure what they're called in MOM6. WIlton, do you know, or could you check?

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On Mon, 17 Apr 2023 at 16:04, Christina Schmidt ***@***.***> wrote: Yes, we decided to run another 5 years and it's running atm. We briefly looked at the density binning, but decided that I would look at it in more detail. So maybe I can look at it first thing tomorrow morning and pause the run in the meantime? What do you mean by "x and y heat flux diagnostics"? — Reply to this email directly, view it on GitHub <#40 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/ACA44U6QH6QSJMULF7WNRQ3XBTMP3ANCNFSM6AAAAAAW4S7JMY> . You are receiving this because you commented.Message ID: ***@***.***>

[schmidt-christina]

I found this variable, is that the right one @adele157 @willaguiar ?

T_advection_xy"  [Unused]
    ! modules: {ocean_model,ocean_model_z,ocean_model_rho2,ocean_model_d2,ocean_model_z_d2,ocean_model_rho2_d2}
    ! long_name: Horizontal convergence of residual mean advective fluxes of heat
    ! units: W m-2
    ! cell_methods: xh:mean yh:mean zl:sum area:mean
    ! variants: {T_advection_xy,T_advection_xy_xyave}

[adele-morrison]

That’s 3D convergence, which would work if we only want circumpolar integrated heat fluxes. Better if we can have the actual x and y fluxes though.

…

On Tue, Apr 18, 2023 at 9:11 AM, Christina Schmidt ***@***.***> wrote: I found this variable, is that the right one @adele157 <https://github.com/adele157> @willaguiar <https://github.com/willaguiar> ? T_advection_xy" [Unused] ! modules: {ocean_model,ocean_model_z,ocean_model_rho2,ocean_model_d2,ocean_model_z_d2,ocean_model_rho2_d2} ! long_name: Horizontal convergence of residual mean advective fluxes of heat ! units: W m-2 ! cell_methods: xh:mean yh:mean zl:sum area:mean ! variants: {T_advection_xy,T_advection_xy_xyave} — Reply to this email directly, view it on GitHub <#40 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/ACA44U5LH4REGSTZ5IKNOETXBXEZPANCNFSM6AAAAAAW4S7JMY> . You are receiving this because you were mentioned.Message ID: ***@***.***>

[willaguiar]

I found this variable, is that the right one @adele157 @willaguiar ?

T_advection_xy"  [Unused]
    ! modules: {ocean_model,ocean_model_z,ocean_model_rho2,ocean_model_d2,ocean_model_z_d2,ocean_model_rho2_d2}
    ! long_name: Horizontal convergence of residual mean advective fluxes of heat
    ! units: W m-2
    ! cell_methods: xh:mean yh:mean zl:sum area:mean
    ! variants: {T_advection_xy,T_advection_xy_xyave}

I believe the fields we want are T_adx, and T_ady

[willaguiar]

I found this variable, is that the right one @adele157 @willaguiar ?

T_advection_xy"  [Unused]
    ! modules: {ocean_model,ocean_model_z,ocean_model_rho2,ocean_model_d2,ocean_model_z_d2,ocean_model_rho2_d2}
    ! long_name: Horizontal convergence of residual mean advective fluxes of heat
    ! units: W m-2
    ! cell_methods: xh:mean yh:mean zl:sum area:mean
    ! variants: {T_advection_xy,T_advection_xy_xyave}

I believe the fields we want are T_adx, and T_ady

 "ocean_model_z","T_adx",        "T_adx",            "ocean_annual_z",     "all", "mean", "none",2
 "ocean_model_z","T_ady",        "T_ady",            "ocean_annual_z",     "all", "mean", "none",2

from: https://github.com/NOAA-GFDL/MOM6-examples/blob/dev/gfdl/ice_ocean_SIS2/OM4_025/diag_table.MOM6

[adele-morrison]

My tests in panan-01 of different surface boundary mixing schemes made zero difference (at least to these overturning diagnostics - I haven't checked SWMT). I started from the orange config and:

1. Used a different set of options in the EPBL scheme (green),
2. Switched off EPBL and turned on KPP (red),
3. Same as for 2, but I also switched on the cvmix convective instability parameterisation (purple).

[adele-morrison]

The same information, but now with a much better diagnostic - cross 1000m isobath transport (thanks to @schmidt-christina for working on the code):

We haven't made a contour for the 1/20th run yet, but would be good to compare that also! And maybe panant-01-zstar-v13 would recover if we ran for longer?

[adele-morrison]

Turns out we don't have salinity restoring turned on in any of the panan configs. This is quite likely the problem!