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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
https://doi.org/10.5194/acp-2017-1135
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
Research article
08 Jan 2018
Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Chemistry and Physics (ACP).
El Niño Southern Oscillation influence on the Asian summer monsoon anticyclone
Xiaolu Yan1,2, Paul Konopka1, Felix Ploeger1, Mengchu Tao1, Rolf Müller1, Jianchun Bian2,3, and Martin Riese1 1Forschungszentrum Jülich (IEK-7: Stratosphere), Jülich, Germany
2Key Laboratory of Middle Atmosphere and Global Environment Observation (LAGEO), Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, China
3College of Earth Science, University of Chinese Academy of Sciences, Beijing, China
Abstract. We analyze the influence of the El Niño Southern Oscillation (ENSO) on the atmospheric circulation and the mean ozone distribution in the tropical and sub-tropical UTLS region. In particular, we focus on the impact of ENSO on the onset of the Asian summer monsoon (ASM) anticyclone. Using the Multivariate ENSO Index, we define climatologies (composites) of atmospheric circulation and composition in the months following El Niño and La Niña (boreal) winters and investigate how ENSO-related flow anomalies propagate into spring and summer. To quantify differences in the divergent and non-divergent part of the flow, the velocity potential (VP) and the stream function (SF) respectively, are calculated from the ERA-Interim reanalysis around the tropical tropopause (potential temperature level θ=380 K). While VP quantifies the well-known ENSO anomalies of the Walker circulation, SF can be used to study the impact of ENSO on the formation of the ASM anticyclone which turns out to be slightly weaker after El Niño than after La Niña winters. In addition, stratospheric intrusions around the eastern flank of the anticyclone into the Tropical Tropopause Layer (TTL) are weaker in the months after strong El Niño events due to more zonally symmetric subtropical jets than after La Niña winters. By using satellite (MLS), in-situ (SHADOZ) observations and model simulations (CLaMS) of ozone, we discuss ENSO-induced differences around the tropical tropopause. Ozone composites show more zonally symmetric features with less in-mixed ozone from the stratosphere into the TTL during and after strong El Niño events and even during the formation of the ASM anticyclone. The difference between El Niño and La Niña composites becomes statistically insignificant in late summer.

Citation: Yan, X., Konopka, P., Ploeger, F., Tao, M., Müller, R., Bian, J., and Riese, M.: El Niño Southern Oscillation influence on the Asian summer monsoon anticyclone, Atmos. Chem. Phys. Discuss., https://doi.org/10.5194/acp-2017-1135, in review, 2018.
Xiaolu Yan et al.
Xiaolu Yan et al.
Xiaolu Yan et al.

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Short summary
Many works investigate the impact of ENSO on the troposphere. However, there are only few works checking the impact of ENSO on the higher altitude. Here, we analyze the impact of ENSO on the vicinity of tropopause using reanalysis, satellite, in-situ and model data. We find that ENSO shows the strongest signal in winter, but its impact can last until the next early summer. ENSO anomaly becomes insignificant in late summer. Our study can help understand the atmosphere propagation after ENSO.
Many works investigate the impact of ENSO on the troposphere. However, there are only few works...
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