The role of low-frequency intraseasonal oscillations in the anomalous Indian summer monsoon rainfall of 2002 |
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Authors: | S Sajani S Naseema Beegum K Krishna Moorthy |
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Institution: | (1) Vikram Sarabhai Space Centre, Trivandrum, 695 022, India |
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Abstract: | We analyze the dynamical features and responsible factors of the low-frequency intraseasonal time scales which influenced
the nature of onset, intensity and duration of active/break phases and withdrawal of the monsoon during the anomalous Indian
summer monsoon of 2002 — the most severe drought recorded in recent times. During that season, persistent warm sea surface
temperature anomalies over the equatorial Indian Ocean played a significant role in modulating the strength of the monsoon
Hadley circulation. This in turn affected the onset and intense break spells especially the long break during the peak monsoon
month of July. Strong low-frequency intraseasonal modulations with significant impact on the onset and active/break phases
occurred in 2002 which were manifested as a good association between low-frequency intraseasonal oscillations and the onset
and active/break spells. Further, SST anomalies over the equatorial Indo-Pacific region on low-frequency intraseasonal time
scales were found to affect the equatorial eastward and thereby off-equatorial northward propagations of enhanced convection
over the Indian region. These propagations in turn modulated the active/break cycle deciding the consequent severity of the
2002 drought. |
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Keywords: | Indian summer monsoon rainfall false onset low-frequency intraseasonal oscillations NPISO Madden-Julian Oscillation |
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