Variability of the aerosol content in the tropical lower stratosphere from 2013 to 2019: impacts of volcanic eruptions.

International audienceModerate volcanic eruptions are a recurrent source of sulfur dioxide (SO2) in the lower stratosphere. The oxidation of SO2 to sulfuric acid aerosol particles enhance the stratospheric aerosol optical depth with likely impact on the climate. Modelling properly the volcanic aerosol content and its evolution in this region is important for radiative impact issues. In this work, we explore the variability of the tropical Upper Troposphere Lower Stratosphere(UTLS) aerosol content between 2013 and 2019, a period which was particularly impacted by volcanic eruptions. For that purpose, space-borne observations from OMPS (datasets from GES DISC and from University of Saskatchewan) and OSIRIS, together with simulations by the Whole Atmosphere Community Climate Model (WACCM) coupled with the Community Aerosol and Radiation Model for Atmospheres (CARMA), are used. Different model sensitive experiments, particularly for the injection altitude and timing, have been conducted to evaluate how the model captures the aerosol plume in terms of content, optical and microphysical properties, transport and residence time. As an example, the results show that the decay of the Calbuco plume observed by OMPS is well reproduced by the model. This study also benefits from unique datasets in the tropical southern hemisphere from the NDACC Maïdo observatory (Reunion Island, France, 20.5°S, 55.5°E) and providing valuable ground-based observations and balloon sounding opportunities. Together with satellite data, we use ground-based aerosol lidar and in situ optical particle counter observations to assess the model performance. A particular focus is made on recent eruptions. The plume of the Ambae volcano (15°S, 167°E) which erupted in July 2018 is shown to propagate to the northern hemisphere with some influence until summer 2019 in the Asian monsoon region. For the year 2019, we investigate how the Ulawun (5°S, 151°E; ~0.14 Tg of SO2) tropical eruption and the Raikoke mid-latitude eruption (48°N, 153°E; ~1.5Tg of SO2), have influenced the aerosol burden in the tropics