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| Titel |
On the low-frequency component of the ENSO-Indian monsoon relationship: a paired proxy perspective |
| VerfasserIn |
M. Berkelhammer, A. Sinha, M. Mudelsee, H. Cheng, K. Yoshimura, J. Biswas |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1814-9324
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| Digitales Dokument |
URL |
| Erschienen |
In: Climate of the Past ; 10, no. 2 ; Nr. 10, no. 2 (2014-04-11), S.733-744 |
| Datensatznummer |
250116949
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| Publikation (Nr.) |
 copernicus.org/cp-10-733-2014.pdf |
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| Zusammenfassung |
| There are a number of clear examples in the instrumental period where
positive El Niño–Southern Oscillation (ENSO) events were coincident with a severely weakened Indian summer
monsoon (ISM). ENSO's influence on ISM precipitation has therefore remained
the centerpiece of various predictive schemes of ISM rainfall for over a
century. The teleconnection between ISM precipitation and ENSO has undergone
a protracted weakening since the late 1980s, suggesting the strength of
ENSO's influence on ISM precipitation may vary on multidecadal timescales.
The recent weakening has occurred despite the fact that the ENSO system has
experienced variance levels during the latter part of the 20th century that
are as high as any period in the past millennium. The recent change in the
ENSO–ISM coupling has prompted questions as to whether this shift represents
a natural mode of climate variability or a fundamental change in ENSO and/or
ISM dynamics due to anthropogenic warming or aerosol impacts on the ISM. Here
we place the 20th century ENSO–ISM relationship in a millennial context by
assessing the phase relationship between the two systems across the time
spectrum using a a series of high-resolution reconstructions of ENSO and the
ISM from tree rings, speleothems and corals. The results from all the proxies
suggest that in the high-frequency domain (5–15 yr), warm (cool) sea
surface temperatures in the eastern tropical Pacific lead to a weakened
(strengthened) monsoon. This finding is consistent with the observed
relationship between the two systems during the instrumental period. However,
in the multidecadal domain (30–90 yr) the phasing between the
systems is reversed such that periods of strong monsoons were, in general,
coincident with periods of enhanced ENSO variability. This result is
counterintuitive to the expectation that enhanced ENSO variance favors an
asymmetric increase in the frequency of El Niño events and therefore a
weakened monsoon system. The finding implies that the prominent multidecadal
variability that characterizes the last 1000 yr of the ISM is not
likely attributable to multidecadal shifts in ENSO. If there is a continued
trend towards enhanced ENSO variance in the coming decades, the results
presented here do not suggest this will force a reduction in ISM
precipitation. |
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