Modulation of Atlantic Basin Tropical Cyclone Activity by the Madden-Julian Oscillation (MJO) Using an Extended MJO Index (1905-2011)

The Madden-Julian Oscillation (MJO) has been documented in many previous studies to impact tropical cyclone (TC) activity for various TC basins around the globe. Strong modulations in Atlantic basin TC activity have also been demonstrated, with enhanced TC activity in the Atlantic Main Development Region (MDR) associated with convective enhancement over the Indian Ocean. Suppressed TC activity is typically observed in the Atlantic MDR when the convectively-enhanced phase of the MJO is over the tropical Pacific. These modulations in the Atlantic seem to be primarily driven by alterations in intraseasonal values of vertical wind shear.

Many studies examining the MJO's impacts utilize the Real-Time Multivariate MJO index which utilizes a combination of outgoing longwave radiation (OLR) and upper- and lower-level zonal winds. OLR is only available since 1974, and consequently, these studies only have 40 years of data with which to work. However, recently, Oliver and Thompson (2012) have developed an extended MJO dataset that goes back to 1905 using surface pressure reconstructions.

A preliminary analysis of this dataset shows similar robust relationships between TC activity and MJO phase extending back to 1905. In addition, given the 100+ years of data available with this new dataset, relationships between MJO phase-TC activity and longer-period indices such as the Atlantic Multidecadal Oscillation and El Niño-Southern Oscillation can also be investigated. These results will be discussed in detail in this presentation.