Influence ofENSO,ENSOModoki, and theIPOon tropical cyclogenesis: a spatial analysis of the southwest Pacific region

Abstract

ABSTRACTTropical cyclones (TCs) pose a significant risk to the nations and territories of the southwest Pacific (SWP). The spatio‐temporal variability ofTCsmakes it challenging to forecast where and when aTCis likely to develop. Therefore, the aim of this study is to better understand the link between large‐scale climatic variability, the environmental conditions required for tropical cyclogenesis (TCgenesis), and the spatial variability ofTCactivity. Three modes of climate variability are investigated: (1) El Niño/Southern Oscillation (ENSO), (2)ENSOModoki, and (3) the Interdecadal Pacific Oscillation (IPO); along withTCgenesis parameters: sea surface temperature; 700hParelative humidity; 700hPavorticity; and vertical wind shear (difference between 200hPaand 850hPawinds). Our findings reaffirm the well‐established northeast/southwest modulation ofTCactivity according to El Niño (EN)/La Niña (LN) using an extendedTCdataset (1945–2011). In addition, new insights into howENSOModoki and theIPOmodulateTCactivity according to phase and season are identified. Importantly, we show that depending on phase, theIPOcan enhance or alter the spatial modulation ofTCgenesis duringENSO/ENSOModoki events, in favour of the northeast/southwest modulations typical ofIPOpositive/negative events. This is particularly the case during the latter half of theSWP TCseason. For example,ENevents that occur withinIPOpositive (negative) epochs result in a shift ofTCactivity up to 1087 km (1288 km) further east (west) during February to April, compared to the typical location ofTCactivity duringENevents. Importantly, these statistical relationships are also associated with anomalously favourable genesis parameters, providing some insights into the physical mechanisms behind the modulations. The findings of this study provide baseline metrics with which to compare climate model simulations and may also facilitate improved seasonal outlooks and better quantification ofTC‐related risks for the vulnerable island nations and territories of theSWP.