Mesoscale Convective Organization Modulated by Convectively Coupled Equatorial Waves

Convectively coupled equatorial waves (CCEWs) are important weathermakers in the tropics and are often linked to high-impact events such as extreme rainfall. Most of such extreme events are caused by mesoscale convective systems (MCSs) embedded within the large-scale CCEWs. While it is established that the development of MCSs in the mid-latitudes is closely linked to favorable environments modulated by synoptic-scale circulations, it is less clear how the CCEWs can modulate mesoscale convective organization and thereby MCS characteristics in the tropics. This work seeks to answer this question by utilizing two complementary satellite observation datasets. We investigate how CCEWs modulate both MCSs as individual entities and the convective elements constituting each MCS. These convective elements include stages of the convective life cycle from shallow, deep convection to mature MCSs. We can therefore relate the CCEW-modulated environment to convective organization. We found that, during the active phase of CCEWs, MCS frequency increases, and MCSs rain harder, produce more lifetime total rain, and grow larger in size. These changes are most pronounced when MCSs are associated with Kelvin waves and tropical depression-type waves while less so with the Madden-Julian Oscillation.

With the advent of global storm-resolving models, results from this work can be used as benchmarks to improve model representation of MCSs as a community effort to further our understanding of convective organization and wave-convection coupling. In addition, while MCSs are difficult to predict in global operational models due to their convective and localized nature, CCEWs can be relatively skillfully predicted beyond 2 weeks. Results from this study can be leveraged for operational forecasts of high-impact MCSs at extended lead times.