Atmospheric impacts from the water-rich 2022 Hunga-Tonga large-magnitude explosive eruption

1. Introduction

A recent NASA "eruption response plan” (Carn et al., 2021) sets out a monitoring strategy for a future Pinatubo-magnitude eruption, to observe the initial progression from plume to dispersed aerosol cloud, and strategies to predict the effects in post-eruption months to years.

2. The water-rich January 2022 Hunga-Tonga eruption

On 15^th January 2022, the Hunga-Tonga volcano (20.5°S, 175.4°W) erupted with an explosivity unprecedented in the satellite era, the energy of the explosion comparable to that from 1883 Krakatau (Wright et al., 2022). The eruption emitted a relatively modest 0.4-0.5Tg of SO₂ (Carn et al., 2022), compared to 14-23Tg for Pinatubo (Guo et al., 2004), but the Krakatau-like phreatomagmatic setting saw the eruptive plume co-detrain 146 +/- 5 Tg of water vapour into the stratosphere (Millan et al., 2022), with the volcanic ash and SO₂.

Several peer-reviewed manuscripts on the Hunga-Tonga atmospheric impacts are still emerging at the time of writing (Nov 2022), Sellitto et al. (2022) showing that the eruption is the first observed case of a net surface warming eruption due to the strong water vapour’s absorption of outgoing long-wave radiation, exceeding the moderate aerosol cooling effect.

The water-rich plume from Hunga-Tonga also changes its effects on the stratospheric ozone layer, heterogeneous chemistry on the volcanic aerosol accelerated in the higher water-content aerosol particles (Zhu et al., 2022). There continues also to be the potential that the 2023 and 2024 Antarctic winter vortices may inherit an unusually high water vapour, with earlier and more widespread polar stratospheric clouds (PSCs) forming.

Three key satellite monitoring sensors that are continuing to monitor the vertical profile of the Hunga-Tonga cloud, to constrain the water vapour, ash and sulphate aerosol: (see Legras et al., 2022).  Two balloon campaigns have measured in-situ the Hunga-Tonga aerosol, from Reunion Island (Jan 2022, e.g. Kloss et al., 2022) and from Sao Paulo (Aug 2022). An Antarctic high-altitude balloon campaign will measure early-season aerosol and PSCs from McMurdo station in April-May 2023. 

3. The PhD project

This PhD project will involve simulations with the UK’ s interactive volcanic aerosol composition-climate model UM-UKCA (Dhomse et al., 2020; Marshall et al., 2019; Dhomse et al., 2014). Model experiments will be designed to understand the progression of the Hunga-Tonga volcanic cloud, and contrast with an ash-rich sulphur-dominated large-magnitude explosive eruption case study such as 2014 Kelud or 1991 Pinatubo.

Two key satellite observing capabilities for Hunga Tonga are the CALIOP and MLS instruments, which have independently observed the progressing altitude and depth of the volcanic aerosol and water vapour layers.  Initial UM-UKCA model simulations have assessed the aerosol cloud's progression, but the project will analyse simulations that resolve also the radiative, microphysical and dynamical influences from the emitted water vapour, which cooled the stratosphere, and have amplified the aerosol radiative effects. The PhD project aligns with the NASA eruption response plan, for greater preparedness to predict the effects from future Krakatau-like sulphur-rich large-magnitude explosive phreatomagmatic eruption within the UK’s Earth System Model (UKESM).

Potential for high impact outcome:

The UM-UKCA model used for this project has world-leading capability to represent volcanic impacts on climate, having well-resolved stratospheric circulation and dynamics, with the radiative-transfer module, interactive PSCs, aerosol microphysics, and chemistry schemes enabling to resolve the different volcanic water vapour influences. The studentship therefore has the potential for ground-breaking paper presenting Hunga-Tonga impacts on the stratosphere, climate and the Antarctic ozone hole.

The atmospheric impacts from the January 2022 Hunga-Tonga eruption are still emerging, and observations of Antarctic polar stratospheric clouds and the ozone layer after previous large-magnitude eruptions (e.g. Gobbi and Adriani, 1993; Deshler et al., 1994) show volcanic impacts were strongest in the austral winter and spring of the 2^nd and 3^rd years after the eruptions (i.e. during 2023 and 2024).

Training:

The student will work under the supervision of Dr Graham Mann, Professor Martyn Chipperfield and Dr Sandip Dhomse, and advice also from Dr. Wuhu Feng (PSC modelling and stratospheric chemistry) and Dr. Alex Rap (radiative transfer modelling).

The successful PhD student will have an opportunity to interact with international project partners to discuss interpreting the model comparisons to observations from field campaigns (Reunion Island, January 2022; Sao Paulo, August 2022) and an upcoming field campaign at McMurdo station, Antarctica at the start of the 2023 Antarctic winter when the Hunga-Tonga water vapour will likely have transported to these high latitudes. Training is organised by the Doctoral Training Programme, the National Centre for Atmospheric Science, and the student will receive funding to attend and present their research at national and international conferences.