Dynamics and composition of the Asian summer monsoon anticyclone
This study places HALO research aircraft observations in the upper-tropospheric Asian summer monsoon anticyclone (ASMA) into the context of regional, intra-annual variability by hindcasts with the ECHAM/MESSy Atmospheric Chemistry (EMAC) model. The observations were obtained during the Earth Sys...
Main Authors: | , , , , , , , , , , , |
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Format: | Article |
Language: | English |
Published: |
Copernicus Publications
2018-04-01
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Series: | Atmospheric Chemistry and Physics |
Online Access: | https://www.atmos-chem-phys.net/18/5655/2018/acp-18-5655-2018.pdf |
Summary: | This study places HALO research aircraft observations in the
upper-tropospheric Asian summer monsoon anticyclone (ASMA) into the context
of regional, intra-annual variability by hindcasts with the ECHAM/MESSy
Atmospheric Chemistry (EMAC) model. The observations were obtained during the
Earth System Model Validation (ESMVal) campaign in September 2012. Observed
and simulated tracer–tracer relations reflect photochemical O<sub>3</sub>
production as well as in-mixing from the lower troposphere and the tropopause
layer. The simulations demonstrate that tropospheric trace gas profiles in
the monsoon season are distinct from those in the rest of the year, and the
measurements reflect the main processes acting throughout the monsoon season.
Net photochemical O<sub>3</sub> production is significantly enhanced in the ASMA,
where uplifted precursors meet increased NO<sub><i>x</i></sub>, mainly produced by
lightning. An analysis of multiple monsoon seasons in the simulation shows
that stratospherically influenced tropopause layer air is regularly entrained
at the eastern ASMA flank and then transported in the southern fringe around
the interior region. Radial transport barriers of the circulation are
effectively overcome by subseasonal dynamical instabilities of the
anticyclone, which occur quite frequently and are of paramount importance for
the trace gas composition of the ASMA. Both the isentropic entrainment of
O<sub>3</sub>-rich air and the photochemical conversion of uplifted O<sub>3</sub>-poor
air tend to increase O<sub>3</sub> in the ASMA outflow. |
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ISSN: | 1680-7316 1680-7324 |