Joint Modulation of Intraseasonal Rainfall in Tropical Australia by the Madden‐Julian Oscillation and El Niño‐Southern Oscillation

Rainfall in tropical Australia is a critical resource for the agricultural sector. However, its high variability implores improvements in our understanding of its variability. Australian tropical rainfall is influenced by both the Madden‐Julian Oscillation (MJO) on intraseasonal time scales and El Niño‐Southern Oscillation (ENSO) on interannual time scales. This study examines the joint relationship between the MJO, ENSO, and tropical Australian rainfall variability. We analyze daily precipitation data from stations across tropical Australia during the wet season (November to April). The wet season rainfall response to the MJO is found to be greater during El Niño than La Niña. We demonstrate that this relationship is not due to the statistical relationship between the MJO and ENSO indices but instead due to differences in how the MJO modulates the large‐scale circulation during El Niño versus during La Niña. Plain Language Summary This manuscript presents studies of the simultaneous relationship between tropical Australian rainfall variability and two modes of climate variability: the Madden‐Julian Oscillation (MJO) and El Niño‐Southern Oscillation (ENSO). We analyze daily rainfall at 43 long‐record (1942–2011) weather stations across tropical Australia during the wet season (November to April). The MJO is shown to increase rainfall in certain phases (phases 5 and 6) and decrease it in other phases (phases 2 and 3), but more importantly, this signal is enhanced during El Niño as compared to La Niña. This is demonstrated to be due to how the MJO influences atmospheric circulation differently in El Niño versus La Niña wet seasons. These results are significant in demonstrating that the MJO and ENSO do not act independently on rainfall; the state of both climate modes need to be known in order to better predict rainfall variability. Agricultural decisions are highly dependent on knowledge of rainfall variability, from crop management on intraseasonal scales to crop types on interannual scales. Overall, the results of this study provide a better understanding of wet season rainfall and its potential predictability in tropical Australia, a major exporter of agriculture and livestock, with implications for improved agricultural decision‐making. Key Points The Madden‐Julian Oscillation (MJO) modulates tropical Australian rainfall This response is enhanced in El Niño periods The effect of ENSO on the MJO‐rainfall connection is independent of the MJO‐ENSO statisti