Tropical Impacts From Polar Vortex Events

Stratospheric sudden warmings and other polar vortex events have well-documented impacts on winter surface weather and climate over middle to high latitudes. However, the scientific understanding of the influence of the polar stratosphere on the tropics remains in its early stages. There are two primary pathways through which these influences can occur. In the first pathway, polar vortex events modulate the strength of the Brewer-Dobson circulation, affecting both the tropical stratosphere and troposphere. In the second pathway, the dynamical downward coupling from the stratosphere into the extratropical troposphere may also influence the tropical troposphere. To investigate the type and magnitude of tropical impacts from polar vortex events, we employ a composite analysis of ERA5 reanalysis data spanning from 1957 to 2024. Our findings reveal that stratosphere-related changes in the Brewer-Dobson circulation not only affect the tropics but also extend into the subtropics and extratropics of the opposite hemisphere. These impacts manifest in various variables, including tropical upwelling, the descent rate of the Quasi-Biennial-Oscillation, tropical stratospheric water vapor, the height and temperature of the tropical tropopause, and tropical column ozone. Furthermore, we find that stratospheric circulation events are associated with shifts in the poleward extent of the tropical Hadley cell. While these tropical changes are generally weaker compared to those observed at higher latitudes, they are nonetheless of comparable duration and statistically significant.