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| Titel |
ENSO influence on the Asian summer monsoon anticyclone as derived from the satellite observations, reanalysis and model simulations |
| VerfasserIn |
Xiaolu Yan, Paul Konopka, Felix Ploeger, Mengchu Tao, Jianchun Bian, Rolf Mueller |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250140207
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| Publikation (Nr.) |
 EGU/EGU2017-3560.pdf |
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| Zusammenfassung |
| El Nino and La Nina are opposite phases of El Nino–Southern Oscillation (ENSO).
The extremes of ENSO patterns have impacts not only on ocean processes, but also
on global weather and climate. The ENSO activities typically show pronounced
features in boreal winter time, but some prolonged events may last for months or
years. In this study we analyze the influence of ENSO on the atmospheric composition
in the tropical and extra-tropical UTLS region in the months following strong ENSO
events. In particular, we are interested in the impact of ENSO on the Asian summer
monsoon (ASM) anticyclone.
Using the Multivariate ENSO Index (MEI), we define two composites starting from strong
El Nino and La Nina winters (|MEI|>0.9) and analyze the anomalies caused by them in the
following months. To quantify the differences in dynamics, the velocity potential (VP)
and the stream function (SF) are calculated based on ERA-Interim reanalysis from 1979 to 2015.
SF shows that during winter the horizontal flow in the tropical UTLS
is dominated by two equatorially symmetric anticyclones resembling the well-known
Matsuno-Gill solution. In summer, the anticyclone in the North Hemisphere is shifted to the ASM region.
VP shows that the centers of the divergent part of the flow lie in the
West Tropical Pacific and Central Pacific for La Nina and El Nino winters, respectively.
These centers move northwestwards during spring and summer.
The anticyclone, subtropical jet and the divergent part of the flow
after La Nina winters are significantly stronger than after El Nino winters.
Based on the MLS measurements of CO, H2O and O3 from 2004 to 2015, we also discuss the respective
anomalies at the tropopause level for the El Nino/La Nina composites. EL Nino composite of
CO shows higher values in the tropical region not only during winter but also during
spring and summer. La Nina composite of H2O shows low anomaly over Maritime Continent
which spread over the whole tropics until summer. The H2O anomalies are consistent with the
respective composites of the outgoing longwave radiation (OLR). O3 composites show
more zonally symmetric features during and after strong El Nino than La Nina events.
We also discuss the distribution of the mean age, H2O and O3 from the CLaMS simulation during
1979-2015. The distributions of mean age and O3 are well-correlated. The patterns of H2O
and O3 distributions from CLaMS show similar features comparing with those from MLS.
The difference between the El Nino/La Nina composites becomes insignificant in late summer.
El Nino episodes which last until the next winter are also selected (1987, 1992 and 1993). The
SF and VP distributions show strongest anomalies during these three years comparing with all
El Nino results. In particular, ASM anticyclone is weak during these periods.
Accordingly, O3 and H2O concentrations in the tropics show weak intrusions from the
subtropics during summer. This indicates that if El Nino does not decay until the following summer,
the ASM anticyclone will be significantly weaker. |
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