Wednesday 29 June 2022

La Niña may re-form later in 2022, BOM

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MELBOURNE, Australia – The 2021–22 La Niña event has reached an end, with a majority of indicators currently at neutral levels, reports the Bureau of Meteorology of the Australian Government in a new update. However, some model outlooks suggest La Niña may re-form later in 2022. As a result, the Bureau’s ENSO Outlook status has moved to La Niña WATCH.

La Niña WATCH means there is around a 50% chance of La Niña forming later in 2022. This is approximately double the normal likelihood.

El Niño–Southern Oscillation (ENSO) indicators have eased further in the past fortnight. Tropical Pacific sea surface temperatures have continued to warm and have been at ENSO-neutral values for the past five weeks.

Similarly, beneath the surface, water temperatures are close to average, or slightly warmer than average. Trade winds are also close to average strength. However, some atmospheric indicators continue to show a La Niña-like signal, including cloudiness along the equator and the Southern Oscillation Index (SOI).

Most climate models surveyed by the Bureau indicate ENSO is likely to remain neutral through the southern hemisphere winter. Four of the seven models surveyed by the Bureau suggest La Niña could return in spring, with the remainder persisting at neutral ENSO levels.

The Indian Ocean Dipole (IOD) is currently neutral. However, the IOD index has been below zero over the past six weeks, with the latest weekly value (−0.49 °C) below the negative IOD threshold value of −0.4 °C. All climate model outlooks surveyed suggest a negative IOD is likely to form over the coming months. A negative IOD increases the chances of above average winter–spring rainfall for much of Australia. It also increases the chances of warmer days and nights for northern Australia.

The Madden–Julian Oscillation (MJO) has recently weakened while in the tropical African region. Models generally suggest a weak or indiscernible signal is most likely for the coming week, meaning there would be little influence on rainfall patterns across the global tropics.

The Southern Annular Mode (SAM) index is currently negative, but is expected to rise to positive values before returning to neutral levels late in June. Neutral SAM has little influence on Australian rainfall.

Sea surface temperatures are currently warmer than average around much of the Australian coastline, particularly to the north and west. This pattern is likely to increase the chance of above average winter–spring rainfall for Australia.

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.

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