CM3 Dev-Eval Working group: Meeting minutes

Earth System Working Group
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CM3 Dev-Eval Working group meeting minutes

Date: Tuesday 21 July at 10:30 am
Participants: @kieranricardo, @MATTENGLAND, @AndyHoggANU, @cbull, @wghuneke, @ariaan, @dkhutch, @sofarrell, @nicolamaher, @ezhilsabareesh8, @ctychung, @saanvi, @ShayneM, @spencerwong, @ClaireT, @aekiss, @Harun_Rashid
Chair: @kieranricardo
Minutes: @spencerwong

Agenda:

CM3 development updates:

  • Several bugs were identified around the tripole fold. These included an error in the CICE angles, a problem with the wind stress remapping, and an issue with updating array halos. These have been fixed in the currently running simulations and resolve the excessive sea ice volumes previously seen in the Arctic.
  • @kieranricardo is working on updating the UM version from 13.0 to 13.8 and swapping to the GC5 central scientific configuration.
    • Still has a strong radiative imbalance and the SST cold bias is stronger.
  • Testing out the CICE C grid, which appears to be stable with the tripole fixes and runoff spreading.
  • Present day and preindustrial test simulations are both currently running and will be available for analysis for the upcoming hackathon.

GitHub issue links to OM3 figures for CM3:

  • @ezhilsabareesh8 Total meridional heat transport

    • Global meridional heat transport is much stronger than OM3 and is closer to observations. Both models are weaker than observations, especially in the southern hemisphere.

  • @ezhilsabareesh8 Time series of annual mean transport through the Indonesian straits

    • Transport through the Indonesian straits is generally close to OM3, but both are quite weak compared to observations. It’s unclear whether this is a topography issue or something else such biases in sea levels or the equatorial undercurrent. Dynamic sea level diagnostics were raised as important for understanding the bias.
    • ACC transport was also discussed, where OM3’s Drake Passage transport closely matches the observed value of 173 Sv. CM3’s Drake Passage transport is much higher, at ~210Sv in the new run, potentially related to the excessive bottom water formation.

  • @ezhilsabareesh8 Zonally integrated overturning

    • The peak overturning looks too strong in CM3. The excessively strong AMOC at 55N has improved, reducing from ~30 to ~20 Sv. This may change in the next set of simulations with the sea ice fixes.

  • @ezhilsabareesh8 Timeseries of global averages

    • The global ocean is warming at a comparable rate to OM3, and faster than CM2.
    • Sea surface temperature is similar to CM2

  • @ezhilsabareesh8 Hovmoller (depth-time) of horizontally averaged temperature drift

    • Warming in the upper 2500m of Atlantic appeared stronger in CM3 compared to CM2, however there was a difference in the simulation years in for the two models. The linked figure has now been updated and the two runs are much more comparable.

  • @ezhilsabareesh8 Surface current speed

    • There are significant biases in the western boundary currents, such as the Gulf stream’s separation. These biases appear fairly typical of 1/4 degree models, and looks quite similar to OM3. Changing the bulk formulation was raised as a potential method of improving these biases.
    • This run was also using the older, higher GM values which may cause the boundary currents to be damped. This isn’t expected to have a large effect here, as the impact on boundary currents in OM3 was quite small.

Note on configuration and code used for the CM3 simulation:

  • The ocean configuration used in the CM3 simulation matches this commit in the OM3 configurations repository, though omits the changes from the commits here and here.
  • There are also differences in the model code versions, as shown in this diff.

Community figures