Variability of the aerosol content in the tropical lower stratosphere from 2013 to 2019 as influenced by moderate volcanic eruptions

Abstract

The cumulative impacts of frequent moderate-magnitude eruptions on stratospheric aerosolswere identified among the factors in recent decadal climate trends. Moderate volcanic eruptionsare a recurrent source of sulfur dioxide (SO2) in the Upper Troposphere and Lower Stratosphere(UTLS) region and the resulting formation of sulfuric acid aerosol particles from the SO2 emittedprovides sites for chemical reactions leading to enhancement of stratospheric optical depth(SAOD) and ozone depletion. Modelling properly the volcanic aerosol content and its evolution inthis region is important for radiative impact issues. In this work, we explore the variability of thetropical UTLS aerosol content between 2013 and 2019, a period which was particularly impactedby moderate tropical and mid-latitude volcanic eruptions. For that purpose, space-borneobservations from OMPS (version 2, datasets from GES DISC), and IASI, together with simulationsby the Whole Atmosphere Community Climate Model (WACCM) coupled with the CommunityAerosol and Radiation Model for Atmospheres (CARMA), are used. Different model sensitiveexperiments, particularly for the injection altitude and timing, have been conducted to evaluatehow the model captures the aerosol plume in terms of content, optical and microphysicalproperties, transport and residence time. We find that the decay of the Calbuco and Kelud plumesobserved by OMPS version 2 is well reproduced by the model. Comparisons with unique datasetsin the tropical southern hemisphere from the NDACC Maïdo observatory (Reunion Island, France,20.5°S, 55.5°E) show good agreement between the lidar SAOD observations and WACCM-CARMASAOD simulations although we observe a difference in the altitude of the maximum aerosolconcentration between the model and the in situ profile after Calbuco eruption in April 2015. Aparticular focus is also made on recent eruptions like Raikoke, Ambae and Ulawun. The plume ofthe Ambae volcano (15°S, 167°E) which erupted in July 2018 is shown to propagate to the northernhemisphere with some influence until summer 2019 in the Asian monsoon region. For the year2019, we investigate how the Ulawun (5°S, 151°E; ~0.14 Tg of SO2) tropical eruption and theRaikoke mid-latitude eruption (48°N, 153°E; ~1.5Tg of SO2), have influenced the aerosol burden in the tropics.