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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
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https://doi.org/10.5194/acp-2020-891
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/acp-2020-891
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  01 Sep 2020

01 Sep 2020

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This preprint is currently under review for the journal ACP.

Upward transport into and within the Asian monsoon anticyclone as inferred from StratoClim trace gas observations

Marc von Hobe1, Felix Ploeger1,5, Paul Konopka1, Corinna Kloss1,2, Alexey Ulanowski3, Vladimir Yushkov3, Fabrizio Ravegnani4, C. Michael Volk5, Laura L. Pan6, Shawn B. Honomichl6, Simone Tilmes6, Douglas E. Kinnison6, Rolando R. Garcia6, and Jonathon S. Wright7 Marc von Hobe et al.
  • 1Institute for Energy and Climate Research (IEK-7), Forschungszentrum Jülich GmbH, 52425 Jülich, Germany
  • 2Laboratoire de Physique et Chimie de l’Environnement et de l’Espace (LPC2E), Université d’Orléans, CNRS, Orléans, France
  • 3Central Aerological Observatory, Dolgoprudnyi, Moscow region, Russia
  • 4CNR Institute of Atmospheric Science and Climate (ISAC), I-10 40129 Bologna, Italy
  • 5University of Wuppertal, Institute for Atmospheric and Environmental Research, Wuppertal, Germany
  • 6National Center for Atmospheric Research (NCAR), POB 3000, Boulder, CO, 80307, USA
  • 7Department of Earth System Science, Tsinghua University, Beijing 100084, China

Abstract. Every year during the Asian summer monsoon season from about mid-June to early September, a stable anticyclonic circulation system forms over the Himalayans. This Asian summer monsoon (ASM) anticyclone has been shown to promote transport of air into the stratosphere from the Asian troposphere, which contains large amounts of anthropogenic pollutants. Essential details of Asian monsoon transport, such as the exact time scales of vertical transport, the role of convection in cross-tropopause exchange, and the main location and level of export from the confined anticyclone to the stratosphere are still not fully resolved. Recent airborne observations from campaigns near the ASM anticyclone edge and centre in 2016 and 2017 respectively show a steady decrease in carbon monoxide (CO) and increase in ozone (O3) with height starting from tropospheric values of 80–100 ppb CO and 30–50 ppb O3 at about 365 K potential temperature. CO mixing ratios reach stratospheric background values of ~ 20 ppb at about 420 K and do not show a significant vertical gradient at higher levels, while ozone continues to increase throughout the altitude range of the aircraft measurements. Nitrous oxide (N2O) remains at or only marginally below its 2017 tropospheric mixing ratio of 326 ppb up to about 400 K, which is above the local tropopause. A decline in N2O mixing ratios that indicates a significant contribution of stratospheric air is only visible above this level. Based on our observations, we draw the following picture of vertical transport and confinement in the ASM anticyclone: rapid convective uplift transports air to near 16 km in altitude, corresponding to potential temperatures up to about 370 K. Although this main convective outflow layer extends above the level of zero radiative heating (LZRH), our observations of CO concentration show little to no evidence of convection actually penetrating the tropopause. Rather, further ascent occurs more slowly, consistent with isentropic vertical velocities of 0.3–0.8 K day−1. For gases not subject to microphysical processes, neither the lapse rate tropopause (LRT) around 380 K nor the cold point tropopause (CPT) around 390 K marks the strong discontinuity of the key tracers (CO, O3, and N2O). Up to about 10 to 20 K above the CPT, isolation of air inside the ASM anticyclone prevents significant in-mixing of stratospheric air. The observed changes in CO and O3 likely result from in-situ chemical processing. Above about 420 K, mixing processes become more significant and the air inside the anticyclone is exported vertically and horizontally into the surrounding stratosphere.

Marc von Hobe et al.

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WACCM simulated Carbon Monoxide (CO) in the Asian Summer Monsoon anticyclone during 2017 StratoClim campaign at different pressure levels Shawn B. Honomichl, Laura L. Pan, and Marc von Hobe https://doi.org/10.5446/48163

Marc von Hobe et al.

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Short summary
The Asian summer monsoon (ASM) is known to foster transport of polluted tropospheric air into the stratosphere. To test and amend our picture of ASM vertical transport, we analyze distributions of airborne trace gas observations up to 20 km altitude near the main ASM vertical conduit south of the Himalayas. We also show that a new high resolution version of the global chemistry climate model WACCM is able to reproduce the observations well.
The Asian summer monsoon (ASM) is known to foster transport of polluted tropospheric air into...
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