Impacts of the Madden-Julian Oscillation on Global Tropical Cyclone Activity

This presentation investigates the impact of the Madden-Julian Oscillation (MJO) on tropical cyclones (TCs) around the globe.  We find that statistically significant modulations of TC activity by the MJO are observed for all TC basins, with enhanced TC activity typically observed during and immediately following the convectively active phases of the MJO.  Thermodynamic parameters such as mid-level moisture and vertical motion show the most significant differences in basins where the MJO is most strongly convectively coupled, such as the Indian Ocean and Northwest Pacific, while dynamic parameters such as vertical wind shear show similar magnitude changes in all TC basins.  Even though the North Atlantic tends to show the smallest changes of any basin for large-scale anomalies, significant modulations in TC activity are still observed there. This study demonstrates significant results over the recent period where the Wheeler-Hendon (WH) MJO index is available (1974-present) and also demonstrates significant skill over an earlier period using the sea level pressure reconstructed MJO index developed by Oliver and Thompson (2011).  Even though both TC records and MJO phase/intensity information become less certain going back in time, MJO phase/TC activity relationships remain remarkably constant.

Given the long period of record, this study also investigates the combined impacts of both the MJO as well as El Nino-Southern Oscillation (ENSO) on TC activity.  In the North Atlantic, La Nina and MJO Phases 1+2 (when MJO convection is located over Africa and the western Indian Ocean) make for extremely active sub-seasonal TC periods, while El Nino and MJO Phases 7+8 (when MJO convection is located over the Western Pacific and the Western Hemisphere) make for extremely active sub-seasonal TC periods in the Northwest Pacific.  We show that similar ENSO/MJO combinations generate extremely active and extremely inactive for most global TC basins.