However, forecasting El Niño is challenging, particularly from March to May when uncertainties are largest due to the autumn predictability barrier, a phenomenon well-known by the agriculture sector. Source: ARC Centre of Excellence for Climate Extremes. The 2002/03 weak El Niño shaded in blue caused widespread impacts on Australia. The strongest events occurred in 1997//16 and are shaded in blue. Dashed red line shows the temperature threshold (NOAA uses +0.5 Celsius) and El Niño events are shaded in red. The index is calculated using the sea surface temperatures in the Niño 3.4 region (area between 170°W-120°W and 5°S-5°N). Figure 2: Time series of the ENSO index from NOAA for 1950 to Feb 20235. increases in cloud cover over the International Date Lineįorecasting agencies, such as the Australian Bureau of Meteorology, consider many of these indicators in seasonal prediction models to determine if an El Niño is underway.westerly wind bursts in the western Pacific Ocean.higher surface air pressure over the western Pacific Ocean and lower pressure in the east.build-up of ocean heat content in the western Pacific Ocean.warming temperatures in the tropical Pacific Ocean.There are several indicators we can look out for when determining if an El Niño is developing: An El Niño usually starts to develop in the Southern Hemisphere autumn and winter, matures in late spring to early summer and then weakens in autumn of the following year. When does El Niño occur?Įl Niño events occur every 3-7 years and can last anywhere from 6 months to 2 years. While El Niño increases the chance of hotter temperatures and reduced rainfall over the east and north of Australia, an El Niño does not guarantee it will be hotter and drier. Both El Niño and La Niña have a large impact on global weather patterns.Įl Niño generally promotes hotter temperatures across Australia, and reduced rainfall in the east and north of Australia.Įl Niño events heighten the risk of heatwaves, drought and bushfires. The opposite state of El Niño is called La Niña, which is associated with a cooling of the central Pacific Ocean and warmer temperatures to the north of Australia. These changes in the ocean and atmosphere interact with each other, forming a coupled ocean-atmosphere interaction known as the El Niño-Southern Oscillation (ENSO). This is due to increased air rising in the east and air sinking in the west. The warming in the east and cooling in the west is accompanied by a weakening of the easterly trade winds and an atmospheric circulation across the equatorial Pacific Ocean known as the Walker Circulation. During El Niño, there is warming of the sea surface temperatures in the central and eastern Pacific Ocean and cooling to the north of Australia (Figure 1). Source: adapted from Bureau of Meteorology.Įl Niño is a naturally occurring ocean-atmosphere phenomenon which has major influences on weather and climate in Australia and the globe. There is increased convection and rainfall over the warm waters in the central and eastern Pacific Ocean, and reduced rainfall over Australia. During El Niño the easterly trade winds weaken, the western Pacific Ocean cools and the central and eastern Pacific Ocean warms. Figure 1: Schematic diagram of El Niño in the tropical Pacific Ocean.
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