Impact of the 2018 Ambae Eruption on the Global Stratospheric Aerosol Layer and Climate

During an extended volcanic unrest starting in 2017, two main moderate stratospheric eruptions occurred at the Ambae volcano (15°S and 167°E), Vanuatu, in April and July 2018. Observations from a geostationary orbit show that the April and July eruptions injected a volcanic plume into the lower stratosphere. While aerosol enhancements from the April eruption have only had an impact on the Southern Hemisphere, the plume from the July eruption was distributed within the lower branch of the Brewer–Dobson circulation to both hemispheres. Satellite, ground-based and in situ observations show that the background aerosol is enhanced throughout the year after the July eruption on a global scale. A volcanic-induced perturbation of the global stratospheric aerosol optical depth up to 0.011 is found, in the ultraviolet/visible spectral range. This perturbation is comparable to that of recent moderate stratospheric eruptions like from Kasatochi, Sarychev, and Nabro. Top of the atmosphere radiative forcing values are estimated between −0.45 and −0.6 W/m² for this event, showing that the Ambae eruption had the strongest climatic impact of the year 2018. Thus, the Ambae eruption in 2018 has to be taken into account when studying the decadal lower stratospheric aerosol budget and in climate studies.