Cloud vertical evolution associated with the MJO life cycle

It is well known that the Madden Julian Oscillation (MJO) is a dominant mode of intraseasonal variability in the tropical atmosphere. The characteristics and structure of the MJO have been extensively studied and well documented by many observational papers and reviews. However, past studies have not clearly shown the vertical evolution of clouds associated with the MJO life cycle due to the limitations of observational data. In this study, ground-based high temporal (~120 s) and vertical (~30 m) resolution radar and lidar datasets from several years of observations at the Atmospheric Radiation Measurement (ARM) Tropical Western Pacific (TWP) site of Manus provide a unique opportunity to examine the vertical structure of clouds associated with the MJO life cycle. Strong MJO events are identified based on the National Oceanic and Atmospheric Administration (NOAA) MJO Index 4 to build up a composite MJO event using both radar/lidar (profiles of cloud frequency and reflectivity) and radiosonde (moisture, temperature, zonal and meridional winds) datasets.

A preliminary result from the composite MJO at Manus shows that the developing trend of cloudiness associated with the MJO life cycle is the sequence of low-middle-high clouds, as suggested by previous studies. This sequence coupled with the moisture and temperature fields confirms the sequence of shallow-deep-stratiform heating structure and the westward tilt in diabatic heating structure, and is consistent with the Discharge-Recharge Mechanism. The strongest MJO events will be analyzed in detail to reveal the cloud evolution and its coherent moist thermodynamic structure. The phase relationship between the MJO convection and the baroclinic structure of zonal wind varies with events at Manus. Examination of how this relationship is associated with tropopause wave structure during the MJO life cycle will help the conceptual and theoretical understanding of MJO.