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How the Natural & Anthropogenic Aerosol Plume over S. E. Asia caused the Millennium Drought
  • Keith Potts
Keith Potts

Corresponding Author:keith.potts@bigpond.com

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The Millennium Drought (Drought) from about 1997 to 2008 was one of if not the most severe drought in recorded Australian history. In 2006 River Murray inflows were 40% below the previous low. Nothing of this severity occurs without a cause, which must have the same time span, and the obvious challenge is to identify the culprit and explain how it caused the Drought. CAWCR Technical Report 26 discussed ENSO; the North West Shelf Sea Surface Temperature (SST); MSLP SE Australia; the SAM; and the Neighbouring Tasman Sea SST as possible causes and found that: local MSLP is the major influence; and ENSO’s influence is created by “large-scale circulation changes”. The literature and the Bureau of Meteorology (BoM) also link the positive phase of the Indian Ocean Dipole (IOD) to drought in Australia. Many researchers have tried to connect ENSO events to volcanic eruptions without success as their focus was on large eruptions which injected gases and tephra into the stratosphere. I include all eruptions in a restricted area, south east Asia (SE Asia), and show how they create ENSO events by reducing convection over the Maritime Continent and forcing the Trade Winds to relax. Simultaneously the volcanic plume moves the regional southern Hadley Cell south and creates the anomalous, persistent high pressure over south eastern Australia. Finally by intercepting the solar radiation by absorption and/or reflection, the volcanic plume cools the sea surface beneath it - the region where moisture which falls as rain in SE Australia evaporates - thereby reducing the available moisture in SE Australia and also creates IOD events. I show that SE Asian tectonic activity is highly variable and the level of volcanic tephra ejected during the Drought was treble the average for the 20th century and this was exacerbated by the anthropogenic aerosols in the same region which increased by 687% from 1979 to 2000 in September. Thus the Millennium Drought was caused by the increased levels of volcanic and anthropogenic aerosols over south east Asia which simultaneously: forced the circulation changes which created the anomalous high pressure over SE Australia; ENSO; and IOD events