资源环境科技发展态势分析平台

Based on observational data analyses of a Madden-Julian Oscillation (MJO) event during the field campaign of the Years of the Maritime Continent Project, we propose a new mechanism for MJO convective initiation and propagation to which mixed Rossby-gravity waves (MRGs) contribute significantly. The intensive observation captured midtropospheric wind variations associated with MRGs, and those signals propagated westward over the Indian Ocean in the MJO-suppressed phase. The transition to the MJO active phase follows tight MRG-convection coupling, which is enhanced when the wavelength becomes shorter due to weak midlevel convergence in the western Indian Ocean. Basin-scale anomalous midtropospheric moistening caused by MRG shallow circulations also contributes. These processes lead to the lower-tropospheric MRG wave packet formation and successive triggering of MJO convection, with the eastward MRG group velocity corresponding to MJO propagation. Additional analysis for other MJO cases implicates potential for robustness of this MJO-MRG relationship.

Plain Language Summary Using the observational data during the field observation campaign, we propose a new mechanism about the initiation and eastward movement of tropical large-scale cumulus convective systems called the Madden-Julian Oscillation (MJO) by focusing on one of high-frequency atmospheric variations in the tropics, mixed Rossby-gravity waves (MRGs). The activation of MJO cloud systems in the western Indian Ocean follows the strong interaction between MRG dynamics and cumulus convection associated with the wavelength shortening of MRGs and broad moistening in the middle troposphere over the Indian Ocean due to MRG shallow circulations. After these processes, MRG circulations in the lower troposphere successively developed to the east, which explains the eastward propagation of MJO convective systems in the Indian Ocean. This study emphasizes the importance of the multiscale interaction between MRGs and MJO.