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Extreme precipitation events over southern India during the year 2015- Curious interactions of El Nino, MJO, and associated waves
  • Rakesh Teja Konduru,
  • Mrudula G
Rakesh Teja Konduru
Department of Geography, Tokyo Metropolitan University, Tokyo, Japan

Corresponding Author:[email protected]

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Mrudula G
2Centre for Electromagnetics (CEM), Council of Scientific and Industrial Research (CSIR), National Aerospace Laboratories (NAL), Kodihalli, Bengaluru, India
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The cause of extreme precipitation events, which deadly flooded Tamil Nadu state of southern India during the northeast monsoon season of 2015 was investigated, and the results were presented in this paper. Though a strong El Nino prevailed during the events, the effect of El Nino is suppressed by the tropical variabilities in the Indian Ocean. A power spectrum analysis was performed to find out the kind of tropical variabilities in NCEP variables like wind fields, Omega, precipitation rate, and soil moisture at 0-10 cm. The spectrum analysis resulted in significant periodicities of 30-40 days and 7-20 days during the extreme events over southern India. Those frequencies were linked with the convectively coupled equatorial waves (CCEWs) like Madden-Julian Oscillations (MJO), and, it was found that the cause of El Nino’s suppression is a manifestation of the CCEWs. The dynamical mechanism behind those interactions was investigated to know the specific connections of two major tropical variabilities El Nino and MJO. Further exploration was done by performing composite analysis of extreme precipitation events during historical El Nino (moderate to very strong) and MJO (active phases over the Indian Ocean) events from 1997-2014 to know the possible interaction between El Nino and MJO. The composite analysis contributed an insight into the interactions of El Nino and MJO. This analysis concludes a hypothesis, which states that if a prevailing, moderate to very strong El Nino as a background low-frequency wave superimposed with high-frequency wave like active MJO in the equatorial Indian Ocean during October-December season, then blended El Nino & MJO wave suppresses the effect of background prevalent El Nino. Such a clampdown of El Nino by blended El Nino & MJO wave roots the cause of extreme precipitation over the southeastern India. This study reveals a new dimension to the El Nino and MJO interactions in intraseasonal time scale, which could be exploited in the prediction of extreme precipitation events during northeast monsoon season.