摘要
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.
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.
基金
supported by the China National 973 Project Grant No.2015CB453200)
the National Natural Science Foundation of China Grant Nos.41475084 and 41230527
the Office of Naval Research Grant No.N000141210450
the International Pacific Research Center(IPRC) sponsored by the Japan Agency for Marine-Earth Science and Technology
