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Impacts of Boreal Winter Monsoon Cold Surges and the Interaction with MJO on Southeast Asia Rainfall

Impacts of Boreal Winter Monsoon Cold Surges and the Interaction with MJO on Southeast Asia Rainfall AbstractTRMM rainfall data from 1998-2012 are used to study the impacts and interactions of Cold Surges (CS) and the Madden-Julian Oscillation (MJO) on rainfall over Southeast Asia during the boreal winter season from November to February. CS are identified using a new large-scale index. The frequencies of occurrences of these two large-scale events are comparable (about 20% of the days each), but the spatial pattern of impacts show differences due to the interactions of the general flow with the complex orography of the region. The largest impact of CS occurs in and around the southern South China Sea due to increased low-level convergence on the windward side of the terrain, and increased shear vorticity off Borneo that enhances the Borneo vortex. The largest impact of the MJO is in the eastern equatorial Indian Ocean, sheltered from CS by the Sumatra Island. In general CS are significantly more likely to trigger extreme rainfall. When both systems are present, the rainfall pattern is mainly controlled by the CS. However, MJO makes the environment more favourable for convection, by moistening the atmosphere and facilitate conditional instability resulting in a significant increased rainfall response compared to CS alone. In addition to the interactions of the two systems in convection, this study confirms a previously identified mechanism in which the MJO may reduce CS frequency through opposing dynamic structures. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Journal of Climate American Meteorological Society

Impacts of Boreal Winter Monsoon Cold Surges and the Interaction with MJO on Southeast Asia Rainfall

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Publisher
American Meteorological Society
Copyright
Copyright © American Meteorological Society
ISSN
1520-0442
eISSN
1520-0442
DOI
10.1175/JCLI-D-16-0546.1
Publisher site
See Article on Publisher Site

Abstract

AbstractTRMM rainfall data from 1998-2012 are used to study the impacts and interactions of Cold Surges (CS) and the Madden-Julian Oscillation (MJO) on rainfall over Southeast Asia during the boreal winter season from November to February. CS are identified using a new large-scale index. The frequencies of occurrences of these two large-scale events are comparable (about 20% of the days each), but the spatial pattern of impacts show differences due to the interactions of the general flow with the complex orography of the region. The largest impact of CS occurs in and around the southern South China Sea due to increased low-level convergence on the windward side of the terrain, and increased shear vorticity off Borneo that enhances the Borneo vortex. The largest impact of the MJO is in the eastern equatorial Indian Ocean, sheltered from CS by the Sumatra Island. In general CS are significantly more likely to trigger extreme rainfall. When both systems are present, the rainfall pattern is mainly controlled by the CS. However, MJO makes the environment more favourable for convection, by moistening the atmosphere and facilitate conditional instability resulting in a significant increased rainfall response compared to CS alone. In addition to the interactions of the two systems in convection, this study confirms a previously identified mechanism in which the MJO may reduce CS frequency through opposing dynamic structures.

Journal

Journal of Climate – American Meteorological Society

Published: Mar 7, 2017

References

  • Northeasterly cold surges and near-equatorial disturbances over the winter MONEX area during December 1974. Part I: Synoptic aspects
    Chang
  • Synoptic disturbances over the equatorial South China Sea and western Maritime Continent during boreal winter
    Chang
  • Annual cycle of Southeast Asia—Maritime Continent rainfall and the asymmetric monsoon transition
    Chang