| Abstrakt: |
A strong Southern Hemisphere (SH) sudden stratospheric warming event occurred in September 2019 and significantly weakened the stratospheric polar vortex. Due to the positive zonal wind anomalies in the troposphere, the barotropic/baroclinic instability, primarily controlled by the horizontal/vertical wind shear, weakened in the upper troposphere at midlatitudes in late September and early October. As a result, planetary waves (PWs) were deflected equatorward near the tropopause rather than upward into the stratosphere, resulting in less perturbation to the stratospheric polar vortex. After October 15, the westward zonal wind anomalies propagate downward and reach the troposphere, increasing the tropospheric barotropic/baroclinic instability. This benefits the propagation of PWs into the stratosphere, leading to the early breaking of the stratospheric polar vortex. In turn, the SH mesosphere becomes anomalously cold due to the stratospheric wind filtering on the gravity waves, leading to the much earlier onset of SH polar mesospheric clouds. Plain Language Summary: A rare sudden stratospheric warming event (SSW), characterized by the dramatic increase in temperature and the weakening of the stratospheric circumpolar flow, occurred in September 2019. The anomalous wind induced by the SSW event tends to propagate downward in the following months. The induced anomalous wind shear can modulate the atmospheric barotropic/baroclinic instability, guiding the propagation of the waves. Along with the downward propagation of the SSW‐induced perturbation, the atmospheric instability increases and benefits the atmospheric waves propagating into the stratosphere from late October to November. The waves propagate into the stratosphere, interact with the mean flow, and contribute to the reversal of the stratospheric zonal wind. The break of the stratospheric polar vortex can also affect the mesosphere by filtering the small‐scale gravity waves, resulting in the perturbation of the temperature, water vapor distribution and the formation of clouds in the mesosphere. Key Points: A rare Southern Hemisphere sudden stratospheric warming event occurred in September 2019 and contributed to the early onset of polar mesospheric clouds in NovemberThe downward propagation of the zonal wind anomaly affects the propagation of planetary waves (PWs) by modulating barotropic/baroclinic instabilityThe secondary enhanced upward propagation of the PWs causes a delayed response in both the polar stratosphere and mesosphere [ABSTRACT FROM AUTHOR] |
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