Modulation of Atlantic Basin Tropical Cyclone Activity by the Madden-Julian Oscillation (MJO) from 1905-2011 (Klotzbach and Oliver, Journal of Climate, 2015)
Abstract: The Madden-Julian Oscillation (MJO) has been demonstrated to play a role in tropical cyclone (TC) activity around the globe in a number of recent studies. While the impact of the MJO on TCs in the Atlantic basin since the mid-1970s has been well documented, a newly-developed 107-year long index for the MJO allows for additional analysis of the impacts of the MJO on Atlantic TC activity. TC activity in the Atlantic increases when MJO-related convection is enhanced over Africa and the Indian Ocean while TC activity in the Atlantic is suppressed when the MJO enhances convection over the West Pacific. This long-term record of the MJO also allows for the analysis of how the MJO's impacts may be modulated by other climate modes, such as the El Niño-Southern Oscillation (ENSO) over interannual timescales and the Atlantic Multi-decadal Oscillation (AMO) over multidecadal time scales. When climatologically unfavorable conditions such as an El Niño event or a negative AMO phase are present, even TC-favorable MJO conditions are not enough to generate statistically significant increases in TC activity from the long-term average across the Atlantic basin. However, climatologically favorable conditions during a La Niña event act to enhance the modulation of TC activity over the Atlantic basin by the MJO.
Variations in global tropical cyclone activity and the Madden-Julian Oscillation since the midtwentieth century (Klotzbach and Oliver, Geophysical Research Letters, 2015)
Abstract: The Madden-Julian oscillation (MJO) has been documented in previous studies to significantly impact tropical cyclone activity in all ocean basins. Most of these studies have utilized the Wheeler-Hendon index. This index is only available since 1974, the period over which remotely sensed outgoing longwave radiation data has been available. Our study utilizes a long reconstructed MJO index, based on surface pressures, which extends back to 1905. We document consistent modulation of tropical cyclone activity by the MJO in all basins over this time period. These modulations are shown to be remarkably stable over the entire analysis period. We also examine the combined impacts of El Niño-Southern Oscillation and the MJO on tropical cyclone activity in each basin over multidecadal time scales.