Transport of trace gases via eddy shedding from the Asian summer monsoon anticyclone and associated impacts on ozone heating rates
<p>The highly vibrant Asian summer monsoon (ASM) anticyclone plays an important role in efficient transport of Asian tropospheric air masses to the extratropical upper troposphere and lower stratosphere (UTLS). In this paper, we demonstrate long-range transport of Asian trace gases via eddy...
| Main Authors: | , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2018-08-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://www.atmos-chem-phys.net/18/11493/2018/acp-18-11493-2018.pdf |
| Summary: | <p>The highly vibrant Asian summer monsoon (ASM) anticyclone plays an important
role in efficient transport of Asian tropospheric air masses to the
extratropical upper troposphere and lower stratosphere (UTLS). In this paper,
we demonstrate long-range transport of Asian trace gases via eddy-shedding
events using MIPAS (Michelson Interferometer for Passive Atmospheric
Sounding) satellite observations, ERA-Interim reanalysis data and the
ECHAM5–HAMMOZ global chemistry-climate model. Model simulations and
observations consistently show that Asian boundary layer trace gases are
lifted to UTLS altitudes in the monsoon anticyclone and are further
transported horizontally eastward and westward by eddies detached from the
anticyclone. We present an event of eddy shedding during 1–8 July 2003 and
discuss a 1995–2016 climatology of eddy-shedding events. Our analysis
indicates that eddies detached from the anticyclone contribute to the
transport of Asian trace gases away from the Asian region to the western Pacific
(20–30° N, 120–150° E) and
western Africa (20–30° N, 0–30° E).
Over the last two decades, the estimated frequency of occurrence of eddy-shedding events is ∼ 68 % towards western Africa and
∼ 25 % towards the western Pacific.</p><p>Model sensitivity experiments considering a 10 % reduction in Asian
emissions of non-methane volatile organic compounds (NMVOCs) and nitrogen
oxides (NO<sub><i>x</i></sub>) were performed with ECHAM5–HAMMOZ to understand the impact
of Asian emissions on the UTLS. The model simulations show that transport of
Asian emissions due to eddy shedding significantly affects the chemical
composition of the upper troposphere ( ∼ 100–400 hPa) and lower
stratosphere ( ∼ 100–80 hPa) over western Africa and the
western Pacific. The 10 % reduction of NMVOCs and NO<sub><i>x</i></sub> Asian emissions
leads to decreases in peroxyacetyl nitrate (PAN) (2 %–10 % near 200–80 hPa),
ozone (1 %–4.5 % near ∼ 150 hPa) and ozone heating rates
(0.001–0.004 K day<sup>−1</sup> near 300–150 hPa) in the upper
troposphere over western Africa and the western Pacific.</p> |
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| ISSN: | 1680-7316 1680-7324 |