The Madden-Julian oscillation (MJO) is one of the most important phenomena associated with intraseasonal atmospheric variability in the tropics. A substantial fraction of tropical precipitation, which plays an important role in the general circulation, falls from the mesoscale convective systems (MCSs) associated with the MJO. Because the MJO modulates other components of the atmosphere-ocean system both in the tropics and extratropics on a wide variety of spatio-temporal scales, the performance of medium range weather forecasting and the realism of pronounced atmospheric and oceanic variability in coupled climate models is substantially dependent on skill in simulating the MJO. Thus, a comprehensive understanding of the MJO is of practical as well as of scientific importance. However, some of the fundamental features of the dynamics and physics of the MJO remain elusive and most currently used general circulation models still have difficulty in simulating the MJO.
Our proposed research aims to improve our understanding of the most crucial but problematic aspect of the MJO, the interplay between convection and large-scale circulation. Because of the inherent complexities associated with the multiscale interaction process of the MJO, a thorough and comprehensive treatment will be the key to any successful diagnosis of MJO dynamics and physics. In this research, we intend to use several innovative methods to accurately identify the internal structures of the MJO. A recently introduced spatio-temporal wavelet transform (STWT) method is capable of localizing a spectral signal from a longitude-time section of a variable. This approach will allow us to document the critical internal structures of the MJO, and in conjunction use with an “object-based” feature tracking approach, examine how such structures regulate the development and organization of MJO convection. Because the degree of vertical development of convection and organization arguably depends strongly on the background moisture field, the role of the internal structures in moisture budget will be assessed in a phenomenological manner.
A comprehensive study based on analysis of in-situ and satellite observations, and the use of a state-of-the-art global cloud-system resolving model NICAM (Nonhydrostatic ICosahedral Atmospheric Model), will greatly improve our chances of success in this project. In addition to these datasets, long-term observational data will be used to derive statistically robust conclusions. Ultra-high resolution long-term cloud data and NICAM simulations that are capable of representing MCSs explicitly provide a promising opportunity to examine multiscale interactions of the MJO.
This is a research project that enhances international collaboration. The objective of this project is entirely in line with the ESS program’s aim “to provide a process-level understanding of the climate system through observation, modeling” and with this call’s aim particularly in two aspects, namely, “improving the understanding of interaction between convection and environmental moisture” and “the dynamic evolution of the cloud population”.