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Climate ChangeNatureScience

Tell-tale El Niño Signal Detectable 18 Months Ahead

 
The El Niño climatic event has long been a driving factor in the way of life of the average Australian, especially if you live away from the city. Dry conditions spread across much of the country, and increase the likelihood of extreme bushfires. Now, a new study has found that any “flavour” of El Niño can be detected 19 months in advance; that’s nine months earlier than was previously possible.

The study was published in the journal Nature Climate Change and was led by Ms Nandini Ramesh, of the Indian Institute of Science, in Bangalore. Ramesh, a pre-PhD student, is presently a researcher at the University of New South Whales Climate Change Research Centre.

Nandini and colleague Raghu Murtugudde happened across their discovery while reviewing decades worth of climatic data relating to El Niño events.

Not all El Niño events follow the same course once they start, nor do they all have the same severity. But according to Nandini, they do all have the same tell-tale discharge of massive volumes of sub-surface warm water from the equatorial western Pacific Ocean. The process had not been noticed prior because it happens sub-surface, where msot satellite measurements take only the surface measurement.

“Satellite observations are only taking the ocean’s skin-temperature, and it turns out that’s not always a good indicator of what’s happening in the top couple of hundred metres, which is a key driver of the El Niño cycle,” says Ramesh.

According to the University of NSW, the “warm water accumulates in the equatorial western Pacific when driven there by persistent trade winds. The researchers say that once the discharge begins in June to August (in the northern hemisphere summer) of the year before the event, the warm water spreads eastward beneath the surface, roughly along the equator.”

And this takes place in every El Niño event, even if surface temperature patterns vary between events.

“We still don’t know what triggers the sub-surface discharge to begin in the first place, and it doesn’t always result in an El Niño event,” says Ramesh. “But we have confirmed that all El Niño events begin this way, which means we can be on the alert for them much, much earlier than before.

“That’s good news for farmers, fire authorities and anyone whose livelihood or wellbeing can benefit from advance warnings like this. It will also improve our theoretical understanding of global climate and how the El Niño cycle may respond to climate change.”

Source: University of New South Whales
Image Source: Neil G Hamilton




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