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20Th Century Intraseasonal Asian Monsoon Dynamics Viewed from Isomap : Volume 20, Issue 5 (08/10/2013)

By Hannachi, A.

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Book Id: WPLBN0003990426
Format Type: PDF Article :
File Size: Pages 17
Reproduction Date: 2015

Title: 20Th Century Intraseasonal Asian Monsoon Dynamics Viewed from Isomap : Volume 20, Issue 5 (08/10/2013)  
Author: Hannachi, A.
Volume: Vol. 20, Issue 5
Language: English
Subject: Science, Nonlinear, Processes
Collections: Periodicals: Journal and Magazine Collection, Copernicus GmbH
Historic
Publication Date:
2013
Publisher: Copernicus Gmbh, Göttingen, Germany
Member Page: Copernicus Publications

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Turner, A. G., & Hannachi, A. (2013). 20Th Century Intraseasonal Asian Monsoon Dynamics Viewed from Isomap : Volume 20, Issue 5 (08/10/2013). Retrieved from http://hawaiilibrary.net/


Description
Description: Department of Meteorology, Stockholm University, Stockholm, Sweden. 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.

Summary
20th century intraseasonal Asian monsoon dynamics viewed from Isomap

Excerpt
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