Ozone Downward Flux Revealed by High-Resolution Differential Absorption Lidar over Tibet during Stratosphere-Troposphere Exchange

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Abstract. This study characterizes a prominent ozone intrusion event driven by STE that occurred on 18–19 October 2017. The analysis is enabled by high spatiotemporal resolution ozone profile observations from the USTC Ozone Lidar deployed at Yangbajing, Tibet (29° N, 99° E). It provides the first lidar-based detection of these rapid ozone descent events and the evidence linking them to temperature variability in the tropopause region through lidar-derived temperature profiles, revealing temperature gradients that generally exceed 8 K km−1 during these events and beyond the resolving capability of conventional atmospheric model products. Combining Wei’s flux diagnostic with a sensitivity test of PV-based dynamical tropopause thresholds identifies 3 PVU as the most suitable definition for this case. ERA5 is then used to characterize the spatiotemporal evolution of cross-tropopause mass fluxes over 25–28° N, 95–99° E, showing that the ozone variations observed by the lidar were modulated by gravity waves associated with the tropopause fold. In addition, lidar-measured ozone profiles are incorporated into a cross-tropopause ozone flux calculation framework, yielding an instantaneous peak STE ozone flux of about 3~4·10-10·kg·s-1·m-2, slightly higher than the corresponding ERA5 value, while maintaining strong agreement in overall flux magnitude and temporal evolution throughout the event. These results show that high-resolution vertical ozone observations and Raman-retrieved temperature profiles from the USTC Ozone Lidar, combined with wind field data, enable accurate quantification of STE-related ozone fluxes. This approach facilitates in-depth investigation of coupled atmospheric composition and dynamical processes.

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