A document by Alexis Mariaccia. Click on the document to view its contents.

We have conducted an investigation into the coupling between the stratosphere and troposphere, focusing on perturbed and unperturbed scenarios of the northern hemisphere polar vortex. These scenarios were established in a previous study, which categorized the main winter typologies based on the timing of sudden stratospheric warmings (SSWs) and final stratospheric warmings (FSWs). Here, we further analyze the mass-weighted divergence of the Eliassen-Palm (EP) flux to confirm the association between these scenarios and the specific timing of momentum and heat flux deposition by planetary waves. Our analysis reveals that wave-1 and wave-2 contributions to this divergence confirm distinct wave activity effects in relation to these scenarios. Additionally, examining the evolutions of the Northern Annular Mode (NAM) provides further insight, demonstrating that these scenarios represent unique states of both the stratosphere and troposphere, which mutually influence each other during the winter months. Of particular interest is the observation of descending stratospheric anomalies into the troposphere following SSWs, often accompanied by a negative phase of the Arctic Oscillation (AO). Notably, we have made an important discovery regarding surface precursors for perturbed scenarios in early winter, specifically December. These surface precursors display wave-like patterns that align with the diagnosed wave activity in the upper stratosphere. This finding establishes a connection between early and late winter, highlighting the importance of these precursors. Consequently, our results enhance our ability to anticipate the behavior of the polar vortex and its impacts, thus holding significant implications for sub-seasonal to seasonal forecasts in the northern hemisphere.

Recent research has put in evidence 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 self-lofting nor 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 eruption of the submarine Hunga volcano in January 2022 was associated with a powerful blast that injected volcanic material to altitudes up to 58 km. From a combination of various types of satellite and ground-based observations supported by transport modeling, we show evidence for an unprecedented increase in the global stratospheric water mass by 13% as compared to climatological levels, and a 5-fold increase of stratospheric aerosol load, the highest in the last three decades. Owing to the extreme injection altitude, the volcanic plume has circumnavigated the Earth in only one week and dispersed nearly pole-to-pole in three months. The unique nature and magnitude of the global stratospheric perturbation by the Hunga eruption ranks it among the most remarkable climatic events in the modern observation era, with a range of potential persistent repercussions for stratospheric composition and climate.