ESM working group: Meeting notes 2024

Earth System Working Group
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29

Date: 15/8/2024

Participants: 15

Chair: @ShayneM

1. Opening and Welcome:

  • We have a speaker for the next meeting on August 29th. There are no speakers confirmed for future meetings beyond this date. Members are encouraged to reach out to Aidan or any co-chair if they are interested in presenting.
  • Future scientific presentations do not need to be fully polished; works in progress or discussion-based topics are welcome.
  • Members were reminded to add any items they want to discuss to the working group agenda via the Esm working group announcement page.

2. Shared Experiments and Usage:

  • The project has used 320 ksu out of the 900 ksu allocated for the quarter.
  • There are currently no new proposals submitted.
  • @dkhutch mentioned that a proposal for 440 ksu from @YanxuanD (Melbourne) is in place, and informal discussions with Gabriel Pontes about a Pliocene simulation might need follow-up.
  • @dkhutch is open to putting forward additional proposals but encourages others to contribute to avoid underutilization of resources.
  • Members have about 6 weeks remaining to use the allocated ksu.
  • Resource usage and allocation will be reviewed approximately 2 weeks before the end of the quarter to adjust as needed.
  • @JulieA raised proposals for the next quarter, including melt water experiments and stratospheric ozone experiments.
    • Melt Water Experiments: @JulieA is working with @MATTENGLAND , @ariaan and @tiloz on anomalous freshwater experiments. They are looking for resources and support, potentially from the NRI (National Research Institute). Technical support and implementation are needed, and they plan to use working group resources.
    • Stratospheric Ozone Experiments: @JulieA is also interested in running CMIP6 DAMIP experiments focused on stratospheric ozone. They may use working group allocations or clicks allocations.
  • @tiloz agreed on the importance of finding resources and support to implement these experiments and suggested putting proposals on the hive for better engagement and support.
  • @LaurieM clarified that while they have used observational constraints for the North Atlantic, they have not yet worked with the new datasets for the South and North Atlantic from recent workshops. They have focused on the North Atlantic but are interested in the new datasets for future experiments.
  • @gpontes confirmed that he has already run historical experiments with North Atlantic meltwater data and has provided experimental designs on the hive. His work is under review.
  • @JulieA explained that the anomalous freshwater forcing dataset is a new dataset developed by a group led by Gavin Schmidt to address missing meltwater in historical CMIP6 experiments. This dataset is intended to be used as a forcing for fast-track CMIP7 experiments. The current goal is to test the dataset with several models to validate its utility before it is officially approved for use.
  • @ShayneM noted that proposals need only a brief summary on the Esm working group page. A simple review by one or two members is required to approve them.
  • @sofarrell raised concerns about how the new anomalous freshwater data would fit with the existing iceberg scheme in ESM 1.6. The new data might complicate the current scheme, which aims to handle freshwater fluxes differently. Siobhan suggested sending links to Rachel for further review. @dhb599 commented that incorporating the new freshwater forcing into ESM 1.5 could be straightforward if the nature of the forcing data is understood. He noted that similar functions have been implemented before and can be adapted for the new data.
  • @JulieA and @dhb599 agreed to take discussions offline to address specific implementation details and integrate the new forcing data into existing models.
  • @JulieA will coordinate a proposal for the melt water experiments and share updates with the group.

3. ACCESS Community Workshop

  • The Earth System Modeling Group needs to finalize the agenda for the half-day workshop by Friday. @dkhutch and @Aidan outlined the current status:
  • Abstracts from the main program will be transferred to the working group day if not included in the main program.
  • There will be two sessions with 15-minute slots for talks (10 minutes plus 5 for Q&A) and additional time allocated for discussion.
  • Additional speakers are encouraged to submit abstracts quickly.
  • @ShayneM suggested the need to link model development and evaluation teams and to propose simulations for model testing and configuration and encouraged members to brainstorm and propose ideas that could unify the group’s efforts and address broader research goals.
  • Co-chairs will finalize the workshop agenda and handle abstract submissions.

4. Science Presentation

@gpontes presented “The Contribution of Meltwater to the 20th Century AMOC Weakening.”

  • Objective: To understand how anomalies related to the Atlantic Meridional Overturning Circulation (AMOC) can propagate to the Southern Hemisphere, focusing on high latitudes and the Southern Ocean.
  • Introduction: Gabriel provided an overview of the AMOC, emphasizing its impact on various climate features and its complex 3D structure. He highlighted the importance of both surface and subsurface currents in understanding AMOC dynamics.
  • Metrics and Observations:
    • Discussed metrics created to measure the warming of the Gulf Stream and the cooling of the Subpolar Gyre.
    • Noted the influence of Atlantic Multidecadal Oscillation (AMO) on AMOC observations and the complexities of evaluating AMOC state due to intrinsic linkages between AMOC and AMO.
  • Model Comparisons:
    • Reviewed reconstructions and measurements of AMOC from various sources, including satellite data and direct measurements.
    • Compared observational trends with climate models (CMIP5 and CMIP6), noting discrepancies, such as the weakening periods not captured by these models.
    • Highlighted a significant observational weakening between 2004 and 2015 that was not reflected in the CMIP models.
  • Study Findings:
    Idealized Experiments Results:
    • Conducted idealized simulations to understand AMOC responses to meltwater inputs.
    • Found that meltwater displaces isopycnals in the North Atlantic, causing AMOC weakening.
    • Models Used: ACCESS-ESM 1.5 and ACCESS-OM2 at quarter-degree resolution.
    • Findings:
      • Kelvin Waves: Meltwater-induced Kelvin waves are generated in the Subpolar Gyre, traveling along the western boundary of the Atlantic and crossing the equator.
      • Impact: These Kelvin waves weaken the Gulf Stream and North Brazil Current, leading to a rapid signal propagation from North to South Atlantic.
      • Rossby Waves: Fast teleconnection via Rossby waves modifies the signal in the South Atlantic, affecting heat transport and AMOC dynamics.
      • Negative Feedback: Rossby waves cause a negative feedback loop by deepening isopycnals in the North Atlantic, potentially strengthening AMOC over decades.
      • Propagation: The signal propagates to South America and North America, influencing both North and South Atlantic regions.
      • Salinity and Temperature Analysis:
        • Salinity Changes: Significant salinity changes observed in the North and South Atlantic, with convergence points influenced by both Kelvin and Rossby waves.
        • Model Comparison: ACCESS-ESM and ACCESS-OM2 models showed similar results regarding salinity dynamics and propagation timescales.
        • New Indices: Developed salinity and SST indices to capture AMOC-related changes more effectively.
    • Historical Data Analysis:
      • Kelvin Signal: Emergence of the Kelvin signal around 1975, with a noticeable trend indicating increasing salinity convergence in the South Atlantic.
      • Rossby Signal: The Rossby signal emerged approximately 20 years after the Kelvin signal, aligning with idealized simulation timescales.
      • SST Indices Comparison:
        • Classical Index: Based on subpolar gyre SST anomalies, showing high variability without significant trends.
        • Corrected Index: Adjusted for polar amplification, revealing a more consistent trend from 1950 onward.
        • Modified SST Dipole Index: Focused on Rossby wave signals, showing a notable emergence around 1975.
    • Model vs. Observations:
      • ACCESS-ESM Model Analysis: Comparison of SST indices from observations with ACCESS-ESM model results, focusing on the timing and magnitude of signal emergence.

Members discussed Gabriel Pontes’ findings, particularly the implications for understanding AMOC dynamics and model accuracy. There was interest in exploring these mechanisms further in ongoing and future research.

Note: These notes were generated by ChatGPT, so please amend as required.

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