Surface and tropospheric ozone trends in the Southern Hemisphere since 1990: possible linkages to poleward expansion of the Hadley circulation

Xiao Lu; Lin Zhang; Yuanhong Zhao; Daniel J Jacob; Yongyun Hu; Lu Hu; Meng Gao; Xiong Liu; Irina Petropavlovskikh; Audra McClure-Begley; Richard Querel

doi:10.1016/j.scib.2018.12.021

Surface and tropospheric ozone trends in the Southern Hemisphere since 1990: possible linkages to poleward expansion of the Hadley circulation

Sci Bull (Beijing). 2019 Mar 30;64(6):400-409. doi: 10.1016/j.scib.2018.12.021. Epub 2018 Dec 28.

Authors

Xiao Lu¹, Lin Zhang², Yuanhong Zhao³, Daniel J Jacob⁴, Yongyun Hu⁵, Lu Hu⁶, Meng Gao⁷, Xiong Liu⁸, Irina Petropavlovskikh⁹, Audra McClure-Begley⁹, Richard Querel¹⁰

Affiliations

¹ Laboratory for Climate and Ocean-Atmosphere Studies, Department of Atmospheric and Oceanic Sciences, School of Physics, Peking University, Beijing 100871, China; School of Engineering and Applied Sciences, Harvard University, Cambridge, MA 02138, USA.
² Laboratory for Climate and Ocean-Atmosphere Studies, Department of Atmospheric and Oceanic Sciences, School of Physics, Peking University, Beijing 100871, China. Electronic address: zhanglg@pku.edu.cn.
³ Laboratory for Climate and Ocean-Atmosphere Studies, Department of Atmospheric and Oceanic Sciences, School of Physics, Peking University, Beijing 100871, China.
⁴ School of Engineering and Applied Sciences, Harvard University, Cambridge, MA 02138, USA; Department of Earth and Planetary Science, Harvard University, Cambridge, MA 02138, USA. Electronic address: djacob@fas.harvard.edu.
⁵ Laboratory for Climate and Ocean-Atmosphere Studies, Department of Atmospheric and Oceanic Sciences, School of Physics, Peking University, Beijing 100871, China. Electronic address: yyhu@pku.edu.cn.
⁶ Department of Chemistry and Biochemistry, University of Montana, Missoula, MT 59812, USA.
⁷ School of Engineering and Applied Sciences, Harvard University, Cambridge, MA 02138, USA.
⁸ Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138, USA.
⁹ Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, USA; NOAA Earth System Research Laboratory, Boulder, CO 80305, USA.
¹⁰ National Institute of Water and Atmospheric Research (NIWA), Lauder 9377, New Zealand.

PMID: 36659731
DOI: 10.1016/j.scib.2018.12.021

Abstract

Increases in free tropospheric ozone over the past two decades are mainly in the Northern Hemisphere that have been widely documented, while ozone trends in the Southern Hemisphere (SH) remain largely unexplained. Here we first show that in-situ and satellite observations document increases of tropospheric ozone in the SH over 1990-2015. We then use a global chemical transport model to diagnose drivers of these trends. We find that increases of anthropogenic emissions (including methane) are not the most significant contributors. Instead, we explain the trend as due to changes in meteorology, and particularly in transport patterns. We propose a possible linkage of the ozone increases to meridional transport pattern shifts driven by poleward expansion of the SH Hadley circulation (SHHC). The SHHC poleward expansion allows more downward transport of ozone from the stratosphere to the troposphere at higher latitudes, and also enhances tropospheric ozone production through stronger lifting of tropical ozone precursors to the upper troposphere. These together may lead to increasing tropospheric ozone in the extratropical SH, particularly in the middle/upper troposphere and in austral autumn. Poleward expansion of the Hadley circulation is partly driven by greenhouse warming, and the associated increase in tropospheric ozone potentially provides a positive climate feedback amplifying the warming that merits further quantification.

Keywords: Hadley circulation poleward expansion; Ozone trend; Southern Hemisphere; Tropospheric ozone; Widening of the tropics.