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

Research output: Contribution to journalArticlepeer-review

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.
Original languageEnglish
Pages (from-to)400-409
Number of pages10
JournalScience Bulletin
Volume64
Issue number6
DOIs
Publication statusPublished - 30 Mar 2019

User-Defined Keywords

  • Tropospheric ozone
  • Ozone trend
  • Southern Hemisphere
  • Hadley circulation poleward expansion
  • Widening of the tropics

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