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https://doi.org/10.5194/acp-2020-980
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/acp-2020-980
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  21 Oct 2020

21 Oct 2020

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This preprint is currently under review for the journal ACP.

Lower-stratospheric aerosol measurements in eastward shedding vortices over Japan from the Asian summer monsoon anticyclone during the summer of 2018

Masatomo Fujiwara1, Tetsu Sakai2, Koichi Shiraishi3, Yoichi Inai4,a, Sergey Khaykin5, Haosen Xi6, Takashi Shibata7, Masato Shiotani8, and Laura L. Pan9 Masatomo Fujiwara et al.
  • 1Faculty of Environmental Earth Science, Hokkaido University, Sapporo, 060-0810, Japan
  • 2Meteorological Research Institute, Japan Meteorological Agency, Tsukuba, 305-0052, Japan
  • 3Faculty of Science, Fukuoka University, Fukuoka, 814-0180, Japan
  • 4Graduate School of Science, Tohoku University, Sendai, 980-8578, Japan
  • 5LATMOS/IPSL, UVSQ, Sorbonne Université, CNRS, Guyancourt, 78280, France
  • 6Graduate School of Environmental Science, Hokkaido University, Sapporo, 060-0810, Japan
  • 7Graduate School of Environmental Studies, Nagoya University, Nagoya, 464-8601, Japan
  • 8Research Institute for Sustainable Humanosphere, Kyoto University, Uji, 611-0011, Japan
  • 9National Center for Atmospheric Research, Boulder, CO 80301, USA
  • anow at: Japan Meteorological Agency, Sapporo, 060-0002, Japan

Abstract. Eastward airmass transport from the Asian summer monsoon (ASM) anticyclone in the upper troposphere and lower stratosphere (UTLS) often involves eastward shedding vortices, which can cover most of the Japanese archipelago. We investigated the aerosol characteristics of these vortices by analysing data from two lidar systems in Japan, at Tsukuba (36.1° N, 140.1° E) and Fukuoka (33.55° N, 130.36° E), during the summer of 2018. We observed several events with enhanced particle signals at Tsukuba at 15.5–18 km altitude (at or above the local tropopause) during August–September 2018, with a backscattering ratio of ~1.10 and particle depolarization of ~5 % (i.e., not spherical, but more spherical than ice crystals). These particle characteristics may be consistent with those of solid aerosol particles, such as ammonium nitrate. Each event had a timescale of a few days. During the same study period, we also observed similar enhanced particle signals in the lower stratosphere at Fukuoka. The upper troposphere is often covered by cirrus clouds at both lidar sites. Backward trajectory calculations for these sites for days with enhanced particle signals in the lower stratosphere and days without indicate that the former airmasses originated within the ASM anticyclone, and the latter more from edge regions. Reanalysis carbon-monoxide and satellite water-vapour data indicate that eastward shedding vortices were involved in the observed aerosol enhancements. Satellite aerosol data confirm that the period and latitudinal region were free from the direct influence of documented volcanic eruptions and high latitude forest fires. Our results indicate that the Asian Tropopause Aerosol Layer (ATAL) over the ASM region extends east towards Japan in association with the eastward shedding vortices, and that lidar systems in Japan can detect at least the lower stratospheric portion of the ATAL during periods when the lower stratosphere is undisturbed by volcanic eruptions and forest fires. The upper tropospheric portion of the ATAL is either depleted by tropospheric processes (convection and wet scavenging) during eastward transport or is obscured by much stronger cirrus cloud signals.

Masatomo Fujiwara et al.

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Masatomo Fujiwara et al.

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Short summary
Lidar aerosol-particle measurements in Japan during the summer of 2018 were found to detect the eastward extension of the Asian Tropopause Aerosol Layer from the Asian Summer Monsoon anticyclone in the lower stratosphere. Analysis of various other data indicate that the observed enhanced particle levels are through eastward shedding vortices from the anticyclone, originating from pollutants emitted from Asian countries and transported vertically by convection in the Asian Summer Monsoon region.
Lidar aerosol-particle measurements in Japan during the summer of 2018 were found to detect the...
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