Modulation of the Northern Polar Vortex by the Hunga Tonga-Hunga Ha’apai Eruption and Associated Surface Response

The January 2022 eruption of Hunga Tonga-Hunga Ha’apai (HTHH) injected unprecedented amounts of water vapour (WV) and sulfur dioxide (SO2) into the stratosphere, significantly impacting the Earth's climate system. Utilizing the Earth System Model SOCOLv4, this study investigates the dynamical implications of the middle-atmosphere disturbances caused by HTHH. A novel dynamical pathway linking water-rich volcanic eruptions to surface climate was identified. The excess stratospheric WV led to significant anomalies in atmospheric circulation, particularly influencing the Northern Hemisphere polar vortex (PV). The findings highlight the potential for such eruptions to modulate the stratospheric PV and subsequent surface climate through altered temperature gradients and weakened polar-night jets, contributing to sudden stratospheric warmings (SSWs). Furthermore, we explain the mechanism dependency on model-projected forcing and its relation to identified biases common also in other chemistry-climate models.