Symmetric and antisymmetric signals in MJO deep convection

We examine the significance of MJO convection asymmetry by building composites of kinematic and thermodynamic fields associated with predominantly symmetric and predominantly antisymmetric MJO convection using ECMWF Interim Reanalysis. The MJO events were identified based on the primary MJO modes extracted via the Nonlinear Laplacian Spectral Analysis on the IR brightness temperature. The features revealed by the composites establish the predominantly antisymmetric MJO convection as a distinctly different signal from its symmetric counterpart. Its accompanying 200-hPa quadrupole anomalous circulation breaks down at initiation over Indian Ocean and when the system passes through the Maritime Continent. Moreover, the MJO convection takes on a summer ISO-like antisymmetric pattern at initiation.

The predominantly symmetric and antisymmetric MJO convection signals were found to differ drastically with respect to their propagation over the Southeast Asia-Australia Maritime Continent. Before reaching the Maritime Continent, symmetric MJO convection sustains the front-to-rear tilted cloud types near the equator. Off the equator, the most enhanced cloud type is likely stratiform. Upon reaching the Maritime Continent, the convection splits into two north-south branches separated by subsidence and dry air intrusion over the equator. The overall strength of the system is reduced. On the other hand, antisymmetric MJO convection often does not exhibit systematic cloud-type transition around the equator. These MJOs are more likely driven by off-equatorial deep convection with stratiform anvils, and are not interrupted when passing the Maritime Continent. The system remains energetic all the way to SPCZ.