Including ash in UKESM1 model simulations of the Raikoke volcanic eruption reveals improved agreement with observations

Abstract

Abstract. In June 2019 the Raikoke volcano, located in the Kuril Islands northeast of the Japanese archipelago, erupted explosively and emitted approximately 1.5 Tg ± 0.2 Tg of SO2 and 0.4–1.8 Tg of ash into the upper troposphere and lower stratosphere. Volcanic ash is usually neglected in modelling stratospheric climate changes since larger particles have generally been considered to be short-lived particles in terms of their stratospheric lifetime. However, recent studies have shown that the coagulation of mixed particles with ash and sulfate is necessary to model the evolution of aerosol size distribution more accurately. We perform simulations using a nudged version of the UK Earth System Model (UKESM1) that includes a detailed two-moment aerosol microphysical scheme for modelling the oxidation of sulfur dioxide (SO2) to sulfate aerosol and the detailed evolution of aerosol microphysics in the stratosphere. We compare the model with a wide range of observational data. The current observational network, including satellites, surface-based lidars, and high-altitude sun photometers means that smaller-scale eruptions such as Raikoke provide unprecedented detail of the evolution of volcanic plumes and processes, but there are significant differences in the evolution of the plume detected using the various satellite retrievals. These differences stem from fundamental differences in detection methods between, e.g. lidar and limb-sounding measurement techniques and the associated differences in detection limits and the geographical areas where robust retrievals are possible. This study highlights that, despite the problems in developing robust and consistent observational constraints, the balance of evidence suggests that including ash in the model emission scheme provides a more accurate simulation of the evolution of the volcanic plume within UKESM1.

Using OMPS-LP color ratio to extract stratospheric aerosol particle median radius and concentration with application to two volcanic eruptions

“…Our result also consistent with the larger particles radius derived by Thomason et al, (2021) and Knepp et al (2022). A recent study by Wells et al (2023) used model simulation and OMPS-LP measurements to show that including ash in the model simulation produces better agreement with the measurements.…”

In-plume and out-of-plume analysis of aerosol-cloud interactions derived from the 2014–15 Holuhraun volcanic eruption

“…Figure 2 and supplementary Figure S2 show the daily mean total column amount of SO2 for the UKESM1-Hol simulations, and the corresponding plume mask and bounding region if derived from the model simulations. In common with simulations of explosive volcanic eruptions that are nudged to ERA reanalyses (Haywood et al, 2010;Wells et al, 2023), the SO2 plume simulated in the model agrees well with the spatial location of the SO2 plume observed from OMPS which gives us confidence in using the SO2 mask derived from observations to evaluate the model simulations. Jordan et al, (2023) also show that the UKESM1-Hol simulations accurately capture the evolution of the volcanic plume in September and October 2014 when compared SO2 retrieved from the IASI (Infrared Atmospheric Sounding Interferometer) satellite instrument.…”

Identifying Climate Impacts From Different Stratospheric Aerosol Injection Strategies in UKESM1

“…The merged stratospheric and tropospheric scheme, StratTrop as described by Archibald et al (2020), simulates interactive chemistry from the surface to the top of the model which includes the oxidation reactions responsible for sulfate aerosol production (Sellar et al, 2019). Evaluation of the evolution of stratospheric aerosols from explosive volcanic eruptions in UKESM1 have been performed and the model shows reasonable fidelity (e.g., Dhomse et al, 2020;Wells, Jones, Osborne, et al, 2023).…”