Joint Modulation of Intraseasonal Rainfall in Tropical Australia by the Madden-Julian Oscillation and El Nino-Southern Oscillation
Ghelani, R.P.S.; Oliver, E.C.J.; Holbrook, N.J.; Wheeler, M.C.; Klotzbach, P.J.
Geophysical Research Letters 44(20): 10754-10761
2017
ISSN/ISBN: 0094-8276 DOI: 10.1002/2017gl075452
Accession: 066348279
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 Nino-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 Nino than La Nina. 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 Nino versus during La Nina. 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 Nino-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 Nino as compared to La Nina. This is demonstrated to be due to how the MJO influences atmospheric circulation differently in El Nino versus La Nina 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.