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Hunga Tonga-Hunga Ha'apai Impacts Activity

HTHH Volcano Impact Model Observations Comparison (HTHH-MOC) Data

Introduction

The 1st January 2022 Hunga eruption was the most explosive eruption in the satellite era (Wright et al., 2022). The shallow underwater explosion reached 58km, and the plume added a very large amount (150 Tg) of water vapour to the stratosphere at an altitude of 30-40km, increasing the global stratospheric water vapour burden by around 10%.

1st Phase of HTHH-MOC

The HTHH-MOC activity was established in 2023, as part of the 3-year Hunga stratospheric impacts cross-activity focus project within the Atmospheric Processes and their Role in Climate (APaRC) activity of the World Climate Research Program, aligned with the upcoming 2026 UNEP/WMO Scientific Assessment of Ozone Depletion report.

Focused primarily on multi-model interactive modeling of the volcanic water and aerosols, and their impacts on atmospheric dynamics, chemistry, and climate, this initial phase of HTHH-MOC established protocols for a set of multi-model experiments (Zhu et al., 2025).

The 2 main experiments in phase 1 were 1) a 10-year forward projection experiment to predict the longevity and impacts from Hunga water vapour and aerosols (e.g., Zhuo et al., 2025; Bednarz et al., 2026), and 2) an interactive CCM re-analysis of the initial two years post-eruption for impacts on the radiative budget (Quaglia et al., 2026) and chemistry (Bednarz et al., 2026).

2nd Phase of HTHH-MOC

The current 2nd phase of HTHH-MOC is organized as part of the new APARC Stratospheric Aerosol activity (since 2025) includes coordinating with Tonga-MIP which focuses on the initial dispersion and progression of the volcanic sulphate aerosol (Clyne et al., 2024).

There will also be further analysis of experiment 2 and related publications (e.g. Aquila et al., 2026) along with the release of the phase 1 datasets to the public via CEDA. A large fraction of the Hunga water vapour still remains in the stratosphere (e.g. Schoeberl et al., 2025), with the latest observational analyses indicating that a return to background conditions will not occur until 2031-2033 (Zhou et al., 2026; Dubé et al., 2026).

Data Archives on JASMIN and CEDA

So far, the HTHH-MOC project data archive is hosted by the UK academic post-processing and archiving system JASMIN) in the United Kingdom. Please follow the link below to gain access to the HTHH-MOC group workspace (or email Graham Mann or Yunqian Zhu for further information).

Part of phase 2 involves making model datasets from phase 1 being made available to researchers via the Centre for Environmental Data Analysis (CEDA), in CF standard formats, for the broader community of interested researchers, and we anticipate the data will be available on CEDA by early 2027.

Our central philosophy is to encourage open discussions between researchers analyzing the model output and the modelling groups. In alignment with the CCMI data-policy and acknowledging the substantial efforts of modelling groups to run these simulations and the subsequent dataset curation, please abide by the HTHH-MOC data access policy outlined below.

Data Policy

This policy aims to encourage community use of HTHH-MOC model datasets, and also ensure that the work of modeling groups is recognized appropriately.

This policy aligns directly with protocols for the APARC activity Chemistry Climate Model Initiative (CCMI), and points 1, 5, 6 and 7 use verbatim identical wording to the CCMI data policy, (see https://blogs.reading.ac.uk/ccmi/ccmi-2022_archive/).

Note that contact information for the Principal Investigators of participating modelling groups and the appropriate scientific reference for the model description papers for each group can be found in Zhu et al. (2025), Table 4.

Data Access Policy

  1. Users of the HTHH-MOC data are to respect the interests of the CCM Principal Investigators (PIs) and their research groups in the interpretation, presentation, and publication of the model output. The best way to achieve this is for routine line of communication to be opened with the model PIs as collaborators to discuss model output and their research. This guideline implicitly recognizes the complexity of the models and interpretive efforts, and the possibility of ongoing scientific work by the model PIs that has yet to be published or otherwise made available to others.
  2. Our phase 2 work plan is to release CMOR-ized and fully CF-compliant phase 1 model datasets to the public via CEDA by the end of February 2027. The HTHH-MOC "interim data archive" on JASMIN, is also available, and researchers are encouraged to use the finalized datasets in the "Exp 1" and "Expt 2a", "Expt 2b" and "Expt 3/Tonga-MIP" archive areas, from the corresponding HTHH-MOC model experiments. For Expt 3 however please note these datasets are in-progress and not yet published in the report or in a peer-reviewed journal article. Note also that the conversion of data to CF standards is done on a voluntary, best-endeavour basis, and whilst we have set the target date above, for some models there may be some time-separations between when new datasets are available in the "interim data-archive", and when they are fully released to the public via the CEDA interface.
  3. For HTHH-MOC datasets fully released to the public, via CEDA, we follow the CCMI data policy for citations, but with a longer 3-year period after release when users are required to offer citation.
    • This 3-year policy allows for the free and open use of model output but includes the obligation to offer co-authorship to model PIs on any manuscripts that are submitted for publication during this time. In return, it is expected that model PIs will constructively participate in the analysis and interpretation of the results.
    • Researchers are kindly asked to provide a brief outline of any planned analysis and a list of the model fields that are central to their work to help avoid duplication and conflicts between groups.
  4. After the 3-year period, users should respect under which the license the data was produced. It is strongly recommended that users send evaluations, draft presentations, or papers to model PIs and the HTHH-MOC coordinators (Yunqian Zhu and Graham Mann)
  5. Within or beyond the 3-year period, any publications using the HTHH-MOC data should properly reference the models that were used and include the following acknowledgement:
    "We acknowledge the modeling groups for making their simulations available for this analysis, the Hunga Tonga-Hunga Ha'apai Volcano Impact Model Observation Comparison (HTHH-MOC) for organizing and coordinating the model data analysis activity, and the Centre for Environmental Data Analysis (CEDA) for collecting and archiving the HTHH-MOC model output."
  6. Occasionally, model output contributed to the archive has been found to contain errors of various sorts. Users who find undetected errors in model output are asked to contact the responsible modeling group, referring to the model contacts in Table 4 of Zhu et al. (2025).
  7. The HTHH-MOC model output is, by default, produced under the Creative Commons Attribution-ShareAlike 4.0 (CC BY-SA 4.0) license. Note, however, that individual modelling groups may choose to make their data available under a different license. Users of the data are expected to respect the license under which the data is made available. If exceptions to the existing license are required for certain uses, please contact the coordinators.

Last modified: Friday, 16-Oct-2026 23:34:23 MDT