Modulation of Precipitation Features by Inertio-Gravity Waves Accompanying a Madden–Julian Oscillation Event over the Tropical Western Pacific

Abstract This study investigated the relative influences of n = 1 westward inertio-gravity (WIGn1), n = 2 westward inertio-gravity (WIGn2), and n = 0 eastward inertio-gravity (EIGn0) waves on precipitation features (areas, heights, and volumetric rainfall) accompanying a Madden–Julian oscillation (MJO) event in the tropical western Pacific, using satellite brightness temperature and shipborne (Research Vessel Mirai ) radar data observed from 20 December 2014 to 17 January 2015. Before the MJO peak, the EIGn0 and WIGn2 waves primarily and secondarily contributed to the variances of the convective precipitation features, whereas their contributions to those of the stratiform precipitation features decreased significantly. Furthermore, the WIGn1 waves substantially increased their contributions and emerged as the dominant contributors to the variances of the stratiform precipitation features, in contrast to their minimal contributions found in the convective precipitation features. After the MJO peak, the WIGn1 and EIGn0 waves became minor contributors, whereas the contributions of the WIGn2 waves remained relatively stable and were comparable to the variances of the convective and stratiform precipitation features. The results of this study imply that before the MJO peak, the EIGn0 and WIGn2 waves preferentially modulated convective precipitation, whereas the WIGn1 waves primarily influenced stratiform precipitation. However, after the MJO peak, the WIGn2 waves became the primary modulators, whereas the EIGn0 and WIGn1 waves exerted only minor modulation of both convective and stratiform precipitation. The WIGn1 and EIGn0 waves played more prominent roles during the development than the decay of MJO-scale convection. Significance Statement This observational study revealed that before the peak of a Madden–Julian oscillation (MJO) event, n = 0 eastward inertio-gravity (EIGn0) and n = 2 westward inertio-gravity (WIGn2) waves preferentially modulated convective precipitation, whereas n = 1 westward inertio-gravity (WIGn1) waves favored the modulation of stratiform precipitation. However, after the MJO peak, only WIGn2 waves exerted significant modulations on both convective and stratiform precipitation. The results of this study illustrate that the WIGn1, WIGn2, and EIGn0 waves are all significant but exert distinct influences on precipitation variations during the evolution of the MJO, which would advance the understanding of inertio-gravity wave modulation of MJO convective activity.