Joint modulation of intraseasonal rainfall in tropical Australia by the Madden-Julian Oscillation and El Niño-Southern Oscillation (Ghelani et al., Geophysical Research Letters, 2017)
Abstract: 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.
Figure: Magnitude of extended wet season rainfall response to the MJO. The magnitude is shown for (a) El Niño, (b) neutral, and (c) La Niña periods. Crossed-out circles are not significant at the 5% level over the analysis period in any of the eight MJO phases. Bold circles are when the largest or smallest anomalies during phases 4–6 or 8–2, respectively, are significant at the 5% level over both the complete analysis period and when restricted to the specific ENSO state.