Modeling Activities

VolMIP is a protocol-driven international project aiming at coordinating the activities of different Research Institutes involved in numerical climate modelling focused on a multi-model assessment of climate models' performance under strong volcanic forcing conditions.

The multi-modeling initiative with closest alignment to the Stratospheric Aerosol Activity continues to be ISA-MIP, which defined in 2018 (Timmreck et. al., 2018) four co-ordinated multi-model experiments for composition climate models with interactive stratospheric aerosol. The ISA-MIP experiments provide a continuing basis to develop and improve the models, with protocols defining benchmark integrations across 3 themes:

• the background/quiescent stratospheric aerosol layer (BG experiment)
• the post-2000 transient stratospheric aerosol record (TAR experiment)
• historical major volcanic aerosol clouds (HErSEA and PoEMS experiments)

After the CoViD period, ISA-MIP resumed multi-model analysis, and benchmark papers in 2023 and 2024 have analysed intercomparisons for BG (Brodowsky et. al., 2024) and HErSEA-Pinatubo experiments (Quaglia et. al., 2023).

A PhD studentship at the BOKU University (Vienna, Austria) analysing the heating of the stratosphere predicted from the interactive HErSEA-Pinatubo integrations, presented at the SSiRC-aligned stratospheric aerosol & volcanic impacts EGU session (Perny et. al., 2025).

Aligned to the HTHH-MOC activity, another recent ISA-MIP multi-model activity of the Hunga aerosol is led by Margot Clyne (now at Colorado State University, formerly Univ. Colorado). The Tonga-MIP experiment assesses how water vapour co-emitted with volcanic SO2 affects an initial descent of volcanic aerosol clouds, and how it affects microphysical progression.

Whilst ISA-MIP remains the primary multi-model activity for the Stratospheric Aerosol Activity, the activity will also continue to align with new experiments in the VolMIP and GeoMIP activities, contributing to CMIP7, including with the new emission-based volcanic forcing dataset (Aubry et. al., 2025).

The ISA-MIP data archive at the German DKRZ data center continues to provide a basis also for new comparative analysis of interactive stratospheric aerosol model data, across the three themes.

The 2022 Hunga eruption was the most explosive volcanic eruption in the satellite era, and the water-rich plume presents an opportunity to understand the impacts on the stratosphere of a large magnitude explosive phreatomagmatic eruption.

The APARC Hunga Impact Activity that was co-initiated by SSiRC, has coordinated research activities and is currently finalizing a special report on Hunga-Tonga impacts that will be published in late 2025 and will directly feed into the upcoming 2026 UNEP/WMO Scientific Assessment of Ozone Depletion report, providing a benchmark synthesis of the impacts from the eruption.

The Hunga Model Observations Comparison (HTHH-MOC) project has been established to assist the success of the report and will continue after 2025 with more analysis and publications and release data to the public.

The project investigates the evolution of volcanic water and aerosols, and their impacts on atmospheric dynamics, chemistry, and climate,using several state-of-the-art chemistry climate models.