Assessing the contribution of ENSO and MJO to the modulation of Australian dust activity based on satellite and ground-based observations

Abstract:

Australian dust may influence regional climate and the marine ecosystems of the surroundings ocean basins. Since most of the southern ocean is iron-limited, the transport and deposition of Australian dust largely determine its productivity and carbon uptake. Yet, the controlling factors of the spatio-temporal variations of Australian dust are not fully understood. Here we assess the connections between observed spatial-temporal variations of Australian dust with key modes of large-scale climate variability, namely the El Niño-Southern Oscillation (ENSO) and Madden-Julian Oscillation (MJO). In particular, multiple dust observations from Aerosol Robotic Network (AERONET), weather stations, and satellite instruments, namely the Moderate Resolution Imaging Spectroradiometer (MODIS) and Multi-angle Imaging SpectroRadiometer (MISR), are examined. The assessed multiple dust observations consistently identify the natural and agricultural dust hotspots in Australia, including the Lake Eyre Basin, Lake Gairdner Basin, Simpson Desert, Barwon-Darling Basin, and Barkly Tableland, as well as a country-wide, austral summertime peak in dust activity. Our regression analysis of observed dust optical depth and climate indices confirms previous modeling work indicating enhanced dust activity in southern and eastern Australia during the subsequent austral summer dust season following the strengthening of austral wintertime El Niño. What our analysis further indicates is the modulation of the ENSO-dust relationship with the MJO phases. According to composites of dust percentage anomalies during sequential MJO phases, dust-active center moves from west to east associated with the eastward propagation of MJO, with maximum enhancement in dust activity at about 120˚E, 130˚E, and 140˚E corresponding to MJO phases 1-2, 3-4, and 5-6, respectively. MJO phases 3-6 are favorable for enhanced ENSO modulation of dust activity, especially the occurrence of extreme dust events, in southeastern Australia.