![]() ![]() The eruption-induced temperature perturbation of the atmosphere may also depend on the phase of the quasi-biennial oscillation (QBO) and the El Niño–Southern Oscillation phenomenon ( Thomas et al., 2009). Aerosol effects on stratospheric ozone may contribute to circulation changes ( Stenchikov et al., 2002). Such an altered circulation of the stratosphere might influence the troposphere, enhancing the probability of a so-called winter warming in northern Eurasia and North America, a feature that has been observed after several large eruptions ( Robock and Mao, 1992). ( 2016), however, argue that further wave-mean flow interaction must be involved in accelerating the vortex. It is, in general, assumed that the cause of the vortex strengthening is the change in the meridional temperature gradient as a result of the aerosol heating being strongest at low latitudes. The Brewer–Dobson circulation (or meridional overturning circulation) is assumed to accelerate due to the tropical heating (e.g., Pitari et al., 2016), and the westerlies of the polar vortices are assumed to be enhanced in the first post-eruption boreal winter (e.g., Azoulay et al., 2021). There is scientific consensus that some features of the stratospheric circulation are altered after large tropical eruptions, which is, however, largely built on modeling results because of the limited number of large eruptions during the satellite era. These temperature anomalies have the potential to alter the middle-atmospheric circulation. Sulfate aerosol additionally absorbs longwave radiation, resulting in a warming of the lower tropical stratosphere. These particles can scatter part of the incoming shortwave radiation back to space and lead to a reduction in the global surface temperature. SO 2 is oxidized to sulfuric acid, which easily forms sulfate particles by heteromolecular nucleation. Strong tropical volcanic eruptions that emit sulfur into the lower stratosphere can have a significant impact on the state of the atmosphere and Earth's climate ( Marshall et al., 2022 Robock, 2000 Timmreck, 2012 Cole-Dai, 2010). This study focuses on the first austral summer after the eruption because mesospheric temperature anomalies are especially relevant for the properties of noctilucent clouds, whose season peaks around January in the Southern Hemisphere. We argue that this is mainly due to intrahemispheric dynamical coupling in the summer hemisphere and is potentially enhanced by interhemispheric coupling with the winter stratosphere. The simulations show a significant warming of the polar summer mesopause of up to 15–21 K in the first November after the eruption. Two experiments with differently parameterized effects of sub-grid-scale orography are compared to test the impact of different atmospheric background states. We use the Upper-Atmospheric ICOsahedral Non-hydrostatic (UA-ICON) model to simulate the atmospheric response to an idealized strong volcanic injection of 20 Tg S into the stratosphere (about twice as much as the eminent 1991 Pinatubo eruption). The aim of this study is to uncover potential dynamical mechanisms that may lead to such a mesospheric temperature response. ![]() Nevertheless, some measurements indicated an increase in mesospheric mid-latitude temperatures after the 1991 Pinatubo eruption. The impact of volcanic eruptions on the mesosphere is less well understood because of a lack of large eruptions in the satellite era and only sparse observations before that period. The dynamical response of the stratosphere to strong volcanic eruptions has been the subject of numerous studies. Explosive volcanic eruptions emitting large amounts of sulfur can alter the temperature of the lower stratosphere and change the circulation of the middle atmosphere. ![]()
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