Unexpected self-lofting and dynamical confinement of volcanic plumes: the Raikoke 2019 case.

Recent research has provided evidence of the self-lofting capacity of smoke aerosols in the stratosphere and their self-confinement by persistent anticyclones, which prolongs their atmospheric residence time and radiative effects. By contrast, the volcanic aerosols-composed mostly of non-absorptive sulphuric acid droplets-were never reported to be subject of dynamical confinement. Here we use high-resolution satellite observations to show that the eruption of Raikoke volcano in June 2019 produced a long-lived stratospheric anticyclone containing 24% of the total erupted mass of sulphur dioxide. The anticyclone persisted for more than 3 months, circumnavigated the globe three times, and ascended diabatically to 27 km altitude through radiative heating of volcanic ash contained by the plume. The mechanism of dynamical confinement has important implications for the planetary-scale transport of volcanic emissions, their stratospheric residence time, and atmospheric radiation balance. It also provides a challenge or "out of sample test" for weather and climate models that should be capable of reproducing similar structures.

The 2010 Antarctic ozone hole: observed reduction in ozone destruction by minor sudden stratospheric warmings.

Satellite observations show that the 2010 Antarctic ozone hole is characterized by anomalously small amounts of photochemical ozone destruction (40-60% less than the 2005-2009 average). Observations from the MLS instrument show that this is mainly related to reduced photochemical ozone destruction between 20-25 km altitude. Lower down between 15-20 km the atmospheric chemical composition and photochemical ozone destruction is unaffected. The modified chemical composition and chemistry between 20-25 km altitude in 2010 is related to the occurrence of a mid-winter minor Antarctic Sudden Stratospheric Warming (SSW). The measurements indicate that the changes in chemical composition are related to downward motion of air masses rather than horizontal mixing, and affect stratospheric chemistry for several months. Since 1979, years with similar anomalously small amounts of ozone destruction are all characterized by either minor or major SSWs, illustrating that their presence has been a necessary pre-condition for reduced Antarctic stratospheric ozone destruction.