The climatological relationship between tropical cyclones in the southwest pacific and the Madden-Julian Oscillation

The focus of this study is the climatological relationship between southwest Pacific Tropical Cyclone (TC) activity and the Madden-Julian Oscillation (MJO) on the interannual time-scale. It investigates TC seasonal characteristics (e.g. cyclogenesis, track morphology, ex-tropical transition, and intensity) as modulated by the phase and intensity of the MJO. The approach is novel as in addition to the focus on the intraseasonal variability of TCs there is also a focus on the interannual variability of TCs even though the MJO is an intraseasonal phenomenon. Links between the MJO, the Southern Annular Mode (SAM) and TC variability are also investigated. Using the MJO phases defined by Wheeler and Hendon (2004), southwest Pacific TC frequency exhibited a statistically significant decrease during MJO phases 2 and 3, and an increase during phases 6 and 7; and during the positive phase of the SAM, an increased frequency of TCs undergoing extratropical transition was observed. In summary, the results show a clear intraseasonal climatological relationship between specific phases of the MJO with respect to a decreased (increased) frequency of TCs during the paired MJO phases 2-3 (6-7); as well as the existence of a statistically significant relationship between the MJO and SAM with respect to the extratropical transition (ETT) of TCs. During positive phases of the SAM, coincident with weak interannual MJO phases 4-5 and 6-7, there are statistically significant greater frequency percentages of TCs undergoing ETT.