The Unusual Impact of the 1997 El Niño on East Australian Spring Rainfall

Wednesday, December 11, 2019 - 08:00
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The 1997-1998 El Niño is by many metrics the strongest El Niño on record. This event had significant impact on regional and global climate. The Earth's surface experienced its warmest year on record at the time in 1998, and regions surrounding the Pacific experienced extreme weather events, such as droughts in Indonesia and floods in Peru. In eastern Australia during spring (September – November), less rainfall than average would typically be expected during an El Niño event, this was seen during the 1982 and 2015 strong El Niño events. In 1997 however, near average east Australian spring rainfall was observed. Explanations for the comparatively unusual rainfall in 1997 range from stochastic weather events, to the remoteness of the peak sea surface temperature anomalies to Australia. In this study, we show our current understanding of how the 1997 El Nino event influenced east Australian spring rainfall. By determining the most important seasonal-scale circulation features for rainfall, we found that the observed wind anomalies during spring 1997 over east Australia were conducive to near average rainfall. Although the east of Australia experienced a widespread positive sea level pressure anomaly associated with the western pole of the Southern Oscillation, the spatial uniformity of this anomaly promoted the near average circulation. Using a 60-member atmospheric model ensemble we conclude that these observed circulation anomalies were primarily forced by the SSTs in 1997. This study has relevance for improving seasonal forecasting and its communication, by improving our understanding of the range of atmospheric impacts that strong El Nino events can generate.

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