Understanding Essential Dynamics and Predictability of Madden-Julian Oscillation (MJO)

University Of Hawaii, Honolulu

Investigators

Abstract

The overall goal of the research is to advance understanding of fundamental mechanisms governing the propagation and development of Madden-Julian Oscillation (MJO) and to improve the ability of dynamical models to simulate and predict intraseasonal variability. Fundamental causes for slow eastward propagation and initiation/intensification of the MJO will be investigated through multi-model diagnostic analysis, and numerical experiments using coupled climate models. Processes through which the MJO teleconnection may feedback to its own eastward propagation will also be examined. The first hypothesis that will be tested focuses on mechanisms determining eastward propagation of the MJO. The coupled Kelvin-Rossby wave structure and the phase difference between the MJO convection and the low pressure anomaly suggest that slow eastward propagation of MJO may be essentially driven by convective interaction with dynamical processes associated with low-frequency equatorial waves. Thus, the coupling low frequency waves and the large scale convective complex (envelope) by frictional moisture convergence may serve as a basic driver for the MJO moving eastward. The local change of moisture, moisture advection, mean state moist static energy (thus SST) distribution, surface entropy flux exchange, upscale eddy transport of momentum, heat and moisture, environmental vertical shear and advection, the extratropical eddy activity flux, and atmosphere-ocean mixed layer interaction can all further modify propagation speed to various degrees. The second hypothesis deals with mechanisms responsible for intensification and maintenance of the MJO. The convective interaction with wave dynamics alone does not generate instability. However, the additional frictional moisture convergence interacting with the latent heat released in shallow and congestus clouds can generate planetary scale instability for MJO intensification through conversion of mean state available moist static energy to MJO available potential and kinetic energy. The moisture advection, the surface evaporation-wind feedback, the interaction between MJO and upscale eddy transport of heat, moisture and momentum, the energy propagation from outside of the tropics may also important for initiation and amplification of the MJO.