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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
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Inter-hemispheric transport is important for understanding the atmospheric tracers because of the asymmetry in emissions between the Southern Hemisphere (SH) and Northern Hemisphere (NH). This study finds that the air masses from the NH extratropics to the atmosphere are about five times larger than those from the SH extratropics. The interplay between the Asian summer monsoon and westerly ducts triggers such cross-equator transport from boreal summer to fall.
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https://doi.org/10.5194/acp-2020-1153
https://doi.org/10.5194/acp-2020-1153

  26 Nov 2020

26 Nov 2020

Review status: this preprint is currently under review for the journal ACP.

Asymmetry and pathways of inter-hemispheric transport in the upper troposphere and lower stratosphere

Xiaolu Yan1,a, Paul Konopka2, Marius Hauck4, Aurélien Podglajen5, and Felix Ploeger2,3 Xiaolu Yan et al.
  • 1State Key Laboratory of Severe Weather & CMA Key Laboratory of Atmospheric Chemistry, Chinese Academy of Meteorological Sciences, Beijing, China
  • 2Institute for Energy and Climate Research: Stratosphere (IEK-7), Forschungszentrum Jülich, Jülich, Germany
  • 3Institute for Atmospheric and Environmental Research, University of Wuppertal, Wuppertal, Germany
  • 4Institute for Atmospheric and Environmental Sciences, Goethe University Frankfurt am Main, Frankfurt am Main, Germany
  • 5Laboratoire de Météorologie Dynamique (LMD/IPSL), École polytechnique, Institut polytechnique de Paris, Sorbonne Université, École normale supérieure, PSL Research University, CNRS, Paris, France
  • aformerly at: Institute for Energy and Climate Research: Stratosphere (IEK-7), Forschungszentrum Jülich, Jülich, Germany

Abstract. Inter-hemispheric transport may strongly affect the trace gas composition of the atmosphere, especially in relation to anthropogenic emissions which originate mainly in the Northern Hemisphere. This study investigates the transport from the boundary surface layer of the Northern Hemispheric (NH) extratropics (30–90° N), Southern Hemispheric (SH) extratropics (30–90° S), and tropics (30° S–30° N) into the global upper troposphere and lower stratosphere (UTLS) using simulations with the Chemical Lagrangian Model of the Stratosphere (CLaMS). In particular, we diagnose inter-hemispheric transport in terms of the air mass fractions (AMF), age spectra, and the mean age of air (AoA) calculated for these three source regions. We find that the AMFs from the NH extratropics to the UTLS are about five times larger than the corresponding contributions from the SH extratropics and almost twenty times smaller than those from the tropics. The amplitude of the AMF seasonal variability originating from the NH extratropics is comparable to that from the tropics. The NH and SH extratropics age spectra show much stronger seasonality compared to the seasonality of the tropical age spectra. The transit time of NH extratropical origin air to the SH extratropics is longer than vice versa. The asymmetry of the inter-hemispheric transport is mainly driven by the Asian summer monsoon (ASM). Both ASM and westerly ducts affect the cross hemispheric transport of the NH extratropical air to the SH, and it is an interplay between the ASM and westerly ducts which triggers such cross-equator transport from boreal summer to fall, mainly westerly ducts over the eastern Atlantic.

Xiaolu Yan et al.

 
Status: open (until 21 Jan 2021)
Status: open (until 21 Jan 2021)
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
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  • RC1: 'review', Darryn Waugh, 08 Dec 2020 Printer-friendly Version
  • RC2: 'review', Anonymous Referee #2, 30 Dec 2020 Printer-friendly Version

Xiaolu Yan et al.

Xiaolu Yan et al.

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Short summary
Inter-hemispheric transport is important for understanding the atmospheric tracers because of the asymmetry in emissions between the Southern Hemisphere (SH) and Northern Hemisphere (NH). This study finds that the air masses from the NH extratropics to the atmosphere are about five times larger than those from the SH extratropics. The interplay between the Asian summer monsoon and westerly ducts triggers such cross-equator transport from boreal summer to fall.
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