A Unique Mechanism of Ozone Surges Jointly Triggered by Deep Stratospheric Intrusions and the Tibetan Plateau Topographic Forcing

Abstract

Given our poor understanding on mechanisms of stratospheric intrusions (SI) upon near-surface ozone (O₃) surges, predicting the SI-induced O₃ pollution pose inherent difficulties. Taking a wintertime O₃ surge episode over the Sichuan Basin (SCB) as an example, we find SI contribute 47.8% to near-surface O₃ levels and reveal the underlying mechanisms. Tropopause folding nearly extends to the deep atmospheric boundary layer over the Tibetan Plateau (TP) due to topographic forcing, driving stratospheric O₃ penetration into the TP's near-surface. The intruded O₃ is subsequently transported into the downstream SCB by strong downdrafts along the TP's leeward slope. Interestingly, the mountain-plains solenoid between the TP and the SCB strengthens the downward intrusions of O₃ during both daytime and nighttime, further amplifying the contribution of SI to the SCB's near-surface O₃ levels. This unique mechanism of O₃ surges could provide new insights for the forecast of unexpected nocturnal high-O₃ episodes.