Observations of the eruption of the Sarychev volcano and simulations using the HadGEM2 climate model.

International audienceIn June 2009 the Sarychev volcano located in the Kuril Islands to the north east of Japan erupted explosively injecting ash and an estimated 1.2±0.2Tg of sulfur dioxide into the upper troposphere and lower stratosphere, making it arguably one of the 10 largest stratospheric injections in the last 50 years. During the period immediately after the eruption, we show that the sulfur dioxide (SO2) cloud was clearly detected by retrievals developed for the IASI satellite instrument and that the resultant stratospheric sulfate aerosol was detected by the OSIRIS limb sounder and CALIPSO lidar. Additional surface-based instrumentation allows assessment of the impact of the eruption on the stratospheric aerosol optical depth. We use a nudged version of the HadGEM2 climate model to investigate how well this state-of-thescience climate model can replicate the distributions of SO2 and sulfate aerosol. The model simulations and OSIRIS measurements suggest that in the northern hemisphere the stratospheric aerosol optical depth was enhanced by around a factor of three (0.01 at 550nm), with resultant impacts upon the radiation budget. The simulations indicate that, in the northern hemisphere for July 2009, the magnitude of the mean radiative impact from the volcanic aerosols is more than 60% of the direct radiative forcing of all anthropogenic aerosols put together. Whilst the cooling induced by the eruption will likely not be detectable in the observational record, the combination of modelling and measurements would provide an ideal framework for simulating future larger volcanic eruptions