Variation of Radar-Observed Precipitation Characteristics in Relation to the Simultaneous Passages of a Madden–Julian Oscillation Event and Convectively Coupled Equatorial Waves during the Years of the Maritime Continent Pilot Study

Abstract

AbstractIn this study, we examined the variations of precipitation morphology and rainfall in relation to the simultaneous passages of a Madden–Julian oscillation (MJO) event and convectively coupled equatorial waves (CCEWs) observed during the Years of the Maritime Continent pilot study. We utilized globally merged infrared brightness temperature data and the radiosonde and radar data observed aboard the Research Vessel Mirai at 4°4′S, 101°54′E. As well as the observed MJO event, equatorial Rossby waves (ERWs), Kelvin waves (KWs), and mixed Rossby–gravity waves (MRGWs) were identified. The radar data exhibited high-frequency variation, mainly caused by KWs and MRGWs, and low-frequency variation, mainly caused by the MJO and ERWs. The MRGWs predominantly modulated convective echo areas and both convective and stratiform volumetric rainfall. In contrast, the MJO event had little influence on the variance of convective echoes. Moreover, stratiform echo areas and volumetric rainfall were more strongly modulated by the combined effects of the MJO, ERWs, KWs, and MRGWs than their convective counterparts. The intense development of stratiform echo areas and volumetric rainfall was coherent with the superimposition of the active phases of the MJO event and all the analyzed CCEWs. The strongest development and a significant reduction of convective echo-top heights before and after the peak MJO date, respectively, were coherent with the passages of ERWs and MRGWs, which were the dominant wave types in modulating echo-top heights. Thus, it appears that the superimposition of the CCEWs on the MJO event exerted complex modulations on the convective activities within the MJO event.