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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
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Volume 18, issue 11 | Copyright
Atmos. Chem. Phys., 18, 8079-8096, 2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 08 Jun 2018

Research article | 08 Jun 2018

El Niño Southern Oscillation influence on the Asian summer monsoon anticyclone

Xiaolu Yan1,2, Paul Konopka1, Felix Ploeger1, Mengchu Tao1, Rolf Müller1, Michelle L. Santee3, Jianchun Bian2,4, and Martin Riese1 Xiaolu Yan et al.
  • 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
  • 3Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA
  • 4College of Earth Science, University of Chinese Academy of Sciences, Beijing, China

Abstract. We analyse the influence of the El Niño Southern Oscillation (ENSO) on the atmospheric circulation and the mean ozone distribution in the tropical and subtropical 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 (MEI), 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 parts of the flow, the velocity potential (VP) and the stream function (SF) are respectively calculated from the ERA-Interim reanalysis in the vicinity of the tropical tropopause at potential temperature level θ = 380K. 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 winters 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) and 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. These isentropic anomalies are overlaid with the well-known anomalies of the faster (slower) Hadley and Brewer–Dobson circulations after El Niño (La Niña) winter. The duration and intensity of El Niño-related anomalies may be reinforced through late summer and autumn if the El Niño conditions last until the following winter.

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Short summary
Many works investigate the impact of ENSO on the troposphere. However, only a few works check the impact of ENSO at higher altitudes. Here, we analyse the impact of ENSO on the vicinity of the 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 early the next summer. The ENSO anomaly is insignificant in late summer. Our study can help to understand the atmosphere propagation after ENSO.
Many works investigate the impact of ENSO on the troposphere. However, only a few works check...