Influence of the Intertropical Convergence Zone/Monsoon Trough on Tropical Cyclogenesis in the Atlantic Basin

Tropical cyclogenesis in the Atlantic Ocean is, in part, influenced by the ITCZ/monsoon trough. The location and extent of the ITCZ, as well as its role in cyclogenesis are modulated by a variety of large scale factors. These factors include seasonal variation, the El Nino-Southern Oscillation (ENSO), and the Madden Julian Oscillation (MJO).

The ITCZ is defined as a contiguous area of mean cyclonic low level vorticity averaged over one month or longer. The monthly variation of percentage of cyclones forming within the ITCZ is studied over the course of the Atlantic hurricane season. Additionally, the roles of intraseasonal and interannual oscillations in the scope and influence of the ITCZ are explored. The Nino3.4 index is utilized to investigate ENSO's role in the ITCZ – tropical cyclogenesis relationship. The role of the MJO in the evolution of the ITCZ, and the number of tropical cyclones (TC) forming within it, is studied in a mean sense through composites based on the Real-time Multivariate MJO index. Significant influence on the location of favorable regions of TC development is found. August and September have a higher proportion of TC's forming within the ITCZ than other months of the Atlantic Hurricane season. Similarly, during phases 2, 3, and 7 of the MJO, and during periods with a negative value of NINO3.4, a greater percentage of tropical cyclogenesis events occur within the ITCZ. Therefore, these are periods during which the ITCZ likely plays a more significant role in cyclogenesis.