Advances in Atmospheric Sciences

, Volume 32, Issue 9, pp 1208–1216 | Cite as

Three-type MJO initiation processes over the Western Equatorial Indian Ocean

  • Shuangli Mei
  • Tim Li
  • Wen Chen


Thirty strong Madden-Julian Oscillation (MJO) events in boreal winter 1982–2001 are selected to investigate the triggering processes of MJO convection over the western equatorial Indian Ocean (IO). These MJO events are classified into three types, according to their dynamic and thermodynamic precursor signals in situ. In Type I, a remarkable increase in low-level moisture occurs, on average, 7 days prior to the convection initiation. This low-level moistening is mainly due to the advection of the background mean moisture by easterly wind anomalies over the equatorial IO. In Type II, lower-tropospheric ascending motion anomalies develop, on average, 4 days prior to the initiation. The cause of this ascending motion anomaly is attributed to the anomalous warm advection, set up by a suppressed MJO phase in the equatorial IO. In Type III, there are no clear dynamic and thermodynamic precursor signals in situ. The convection might be triggered by energy accumulation in the upper layer associated with Rossby wave activity fluxes originated from the midlatitudes.

Key words

MJO Indian Ocean dynamic precursor signal thermodynamic precursor signal 


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Copyright information

© Chinese National Committee for International Association of Meteorology and Atmospheric Sciences, Institute of Atmospheric Physics, Science Press and Springer-Verlag Berlin Heidelberg 2015

Authors and Affiliations

  1. 1.Center for Monsoon System Research, Institute of Atmospheric PhysicsChinese Academy of SciencesBeijingChina
  2. 2.University of Chinese Academy of SciencesBeijingChina
  3. 3.International Laboratory on Climate and Environment Change and Key Laboratory of Meteorological Disaster of Ministry of EducationNanjing University of Information Science and TechnologyNanjingChina
  4. 4.International Pacific Research Center, Department of Meteorology, School of Ocean and Earth Science and TechnologyUniversity of Hawaii at ManoaHonoluluUSA

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