Friday 19 August 2022

The negative Indian Ocean Dipole is under way, La Niña Watch continues

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MELBOURNE, Australia – According to the latest report from the Bureau of Meteorology (BOM) of the Australian Government, a negative Indian Ocean Dipole (IOD) event is under way. The IOD index has been very close to or exceeded negative IOD thresholds (i.e., at or below −0.4 °C) over the past eight weeks. All climate model outlooks surveyed indicate that negative IOD conditions are likely to continue into late spring. A negative IOD event is associated with above average winter–spring rainfall for much of Australia.

The Bureau’s ENSO Outlook remains at La Niña WATCH, meaning there is around a 50% chance (double the normal likelihood) of La Niña forming later in 2022. This is a result of current observations and model outlooks. La Niña events increase the chance of above average winter–spring rainfall across much of northern and eastern Australia

El Niño–Southern Oscillation (ENSO) ocean indicators are currently at neutral levels. However, some atmospheric indicators, such as the Southern Oscillation Index, continue to show a residual La Niña-like signal. Trade winds have also recently re-strengthened in the western Pacific (more La Niña-like).

Three of seven climate models surveyed by the Bureau suggest La Niña could return in early southern hemisphere spring, with a fourth in late spring. The remaining three models persist at neutral ENSO levels.

The Madden–Julian Oscillation (MJO) is currently weak. Most models suggest the MJO is likely to remain weak or indiscernible over the coming week. The means it is likely to exert little or no influence on global tropical weather.

The Southern Annular Mode (SAM) index is currently neutral, with neutral to weakly positive values forecast for the rest of August. Positive SAM has a drying influence for parts of south-west and south-east Australia, while neutral SAM has little influence on Australian rainfall.

Climate change continues to influence Australian and global climate. Australia’s climate has warmed by around 1.47 °C for the 1910–2020 period. Southern Australia has seen a reduction of 10–20% in cool season (April–October) rainfall in recent decades.There has also been a trend towards a greater proportion of rainfall from high intensity short duration rainfall events, especially across northern Australia.

Please note: ENSO and IOD index values are based on data available at the time of publication. Some data that is used to create our global ocean maps was not available within the usual timeframe. This is due to an external issue, outside of the Bureau’s control.

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