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| Titel |
20th century intraseasonal Asian monsoon dynamics viewed from Isomap |
| VerfasserIn |
A. Hannachi, A. G. Turner |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1023-5809
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| Digitales Dokument |
URL |
| Erschienen |
In: Nonlinear Processes in Geophysics ; 20, no. 5 ; Nr. 20, no. 5 (2013-10-08), S.725-741 |
| Datensatznummer |
250086052
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| Publikation (Nr.) |
 copernicus.org/npg-20-725-2013.pdf |
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| Zusammenfassung |
| The Asian summer monsoon is a high-dimensional and highly nonlinear
phenomenon involving considerable moisture transport towards land from the
ocean, and is critical for the whole region. We have used daily ECMWF
reanalysis (ERA-40) sea-level pressure (SLP) anomalies on the seasonal cycle,
over the region 50–145° E, 20° S–35° N, to study
the nonlinearity of the Asian monsoon using Isomap. We have focused on the
two-dimensional embedding of the SLP anomalies for ease of interpretation.
Unlike the unimodality obtained from tests performed in empirical orthogonal
function space, the probability density function, within the two-dimensional
Isomap space, turns out to be bimodal. But a clustering procedure applied to
the SLP data reveals support for three clusters, which are identified using a
three-component bivariate Gaussian mixture model. The modes are found to
appear similar to active and break phases of the monsoon over South Asia in
addition to a third phase, which shows active conditions over the western
North Pacific. Using the low-level wind field anomalies, the active phase over
South Asia is found to be characterised by a strengthening and an eastward
extension of the Somali jet. However during the break phase, the Somali jet is
weakened near southern India, while the monsoon trough in northern India also
weakens. Interpretation is aided using the APHRODITE gridded land
precipitation product for monsoon Asia. The effect of large-scale seasonal
mean monsoon and lower boundary forcing, in the form of ENSO, is also
investigated and discussed. The outcome here is that ENSO is shown to perturb
the intraseasonal regimes, in agreement with conceptual ideas. |
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