Further Exploration of MJO Initiation Events and Precursors as Revealed by an MJO-like Dynamical Mode

The Madden Julian Oscillation (MJO) is a tropical phenomenon that develops over the Indian Ocean as a large area of convection approximately 1000km across. This intraseasonal oscillation affects both weather and climate in extratropical regions, where most of the world’s population resides. However, computational models do not represent the MJO adequately, and the scientific community has turned its attention to the MJO’s initial stages. This research studies Primary MJO events (those arising in the absence of a pre-existing MJO signal) identified by four methods developed by previous researchers. Two of the methods focus mainly on precipitation while the other two focus on circulation. A multivariate MJO-like dynamical mode, obtained from unfiltered five-day-mean gridded data, was used to visualize the events during the 1998-2009 boreal winters. The contributions made to the MJO-like mode by the following variables were analyzed: outgoing long-wave radiation (OLR), sea level pressure (SLP), mid-tropospheric temperature (T400), and upper- and lower-level zonal winds (u200hPa and u850hPa). The mode was able to depict typical eastward-propagating events, and it was also able to show westward-propagating and non-propagating events seen by other researchers. In addition, the mode depicts extratropical interactions and the areas of suppressed convection preceding events, as noted by previous studies. However, the mode did not represent convection of all of the selected events. The study shows that the multivariate MJO-like dynamical mode was able to capture the complexity of MJO events, making it a useful tool for future MJO studies.