傅 強教授

Department of Atmospheric Sciences, University of Washington

Abstract

Stratosphere-troposphere exchange (STE) of ozone represents a significant source for the tropospheric ozone budget. The STE of ozone can substantially impact the surface ozone concentrations and thus air quality. The STE of ozone can also modify the tropospheric oxidation capacity, methane lifetime, and other atmospheric constituents' chemical cycles.

The air mass and ozone STEs are often quantified using the lowermost stratosphere mass budget approach proposed by Appenzeller, Holton and Rosenlof (1996). We recently modified this approach by employing the dynamic isentropic surface fitted to the tropical tropopause instead of a fix level (e.g., 380 K or 100 hPa) as the top boundary of the lowermost stratosphere (Wang et al., 2022), which is critically important in examining the response of STEs to climate changes. Furthermore, we found that in the present climate, the annual-mean tropical upward ozone fluxes – previously overlooked – amount to about 190 Tg/year. This upward flux offsets about 35% of the extratropical net downward ozone flux (~530 Tg/year), leading to a global ozone STE of ~340 Tg/year (Wang and Fu, 2021). The latter should be used as the ozone STE contribution to the tropospheric ozone budget.

In this talk, we will present the ozone STE in the Last Glacial Maximum based on WACMM6 simulation and ozone STE in CCMI models from 1960-2099 using our modified lowermost stratosphere mass budget approach (Wang et al., 2022; Wang and Fu, 2023). We will also discuss the role of the El Nino–Southern Oscillation, quasi-biennial oscillation, and Brewer-Dobson circulation in controlling the interannual variability of ozone STE in the present climate (Wang et al., 2023).

邀請人 : 李威良