Stratospheric aerosol layer perturbation caused by the 2019 Raikoke and Ulawun eruptions and their radiative forcing

Corinna Kloss,Ghassan Taha,Pasquale Sellitto,Felix Ploeger,Fabrice Jégou,Gwenaël Berthet,Jean-Baptiste Renard,Bernard Legras,Maxim Eremenko,Adriana Bossolasco,Mariam Tidiga

doi:10.5194/acp-21-535-2021

Abstract

Abstract. In June 2019 a stratospheric eruption occurred at Raikoke (48∘ N, 153∘ E). Satellite observations show the injection of ash and SO2 into the lower stratosphere and an early entrainment of the plume into a cyclone. Following the Raikoke eruption, stratospheric aerosol optical depth (sAOD) values increased in the whole Northern Hemisphere and tropics and remained enhanced for more than 1 year, with peak values at 0.040 (short-wavelength, high northern latitudes) to 0.025 (short-wavelength, Northern Hemisphere average). Discrepancies between observations and global model simulations indicate that ash may have influenced the extent and evolution of the sAOD. Top of the atmosphere radiative forcings are estimated at values between −0.3 and -0.4Wm-2 (clear-sky) and of −0.1 to -0.2Wm-2 (all-sky), comparable to what was estimated for the Sarychev eruption in 2009. Almost simultaneously two significantly smaller stratospheric eruptions occurred at Ulawun (5∘ S, 151∘ E) in June and August. Aerosol enhancements from the Ulawun eruptions mainly had an impact on the tropics and Southern Hemisphere. The Ulawun plume circled the Earth within 1 month in the tropics. Peak shorter-wavelength sAOD values at 0.01 are found in the tropics following the Ulawun eruptions and a radiative forcing not exceeding −0.15 (clear-sky) and −0.05 (all-sky). Compared to the Canadian fires (2017), Ambae eruption (2018), Ulawun (2019) and the Australian fires (2019/2020), the highest sAOD and radiative forcing values are found for the Raikoke eruption.

Highlights

Severe volcanic eruptions can inject a significant amount of sulfur-containing species and, potentially, ash material directly into the UTLS (Upper Troposphere–Lower Stratosphere)
An OMPS aerosol extinction profile, which was observed on 22 June 2019 02:26 UTC at 49◦ N and 154◦ E, displays an enhanced aerosol signal at ≈ 14 km altitude that is compatible with previous estimates (e.g., Muser et al, 2020)
We show that during the past 3 years, the highest peak stratospheric aerosol optical depth (sAOD) values resulted from the Raikoke eruption

Summary

Introduction

Severe volcanic eruptions can inject a significant amount of sulfur-containing species and, potentially, ash material directly into the UTLS (Upper Troposphere–Lower Stratosphere). C. Kloss et al.: Stratospheric aerosol layer perturbation caused by the 2019 Raikoke and Ulawun eruptions altitude, and (4) dynamical situation at the time and location of the injection. (1) The sulfur burden in the plume determines the resulting sulfate aerosol formation and dominates the climate impact (Kremser et al, 2016). (2) A tropical volcano producing sulfate material into the UTLS usually has a larger geographical impact than a sized eruption at higher latitudes. A higher injection altitude results in a longer potential transport within the BDC and a longer sedimentation time, which leads to a longer potential lifetime of the formed or pre-existing aerosol. A higher injection altitude results in a longer potential transport within the BDC and a longer sedimentation time, which leads to a longer potential lifetime of the formed or pre-existing aerosol. (4) The dynamical situation around the plume (cyclones, anticyclones, jets, etc.) can modify the transport pathways and, in some cases, lead to a fast transport/distribution (Fairlie et al, 2014; Wu et al, 2017)

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