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The Australian Bureau of Meteorology has retained its ‘El Nino alert’, signalling an approximately 70 per cent chance for the warming event to occur in the East Equatorial Pacific. It also represents triple the normal likelihood of the eventuality, the Bureau said in its update on Tuesday. Back home, the India Meteorological Department (IMD) has assessed that the current weak El Nino conditions may persist until June.
An El Nino has often, but not always, been associated with a poor monsoon in India. In contrast, La Nina has mostly helped the cause of the monsoon. During El Nino, sea-level pressure tends to be lower in the Eastern Pacific and higher in the Western Pacific (in other words, warmer ocean waters in the East and colder in the West). The opposite tends to occur during a La Nina.
The Bureau said sea-surface temperatures have remained close to El Nino thresholds for the past five weeks. The atmosphere has responded only at times, and is yet to show a consistent El Nino-like response.
Interaction of the atmosphere and ocean (coupling) is an essential part of El Nino and La Nina events. The warming of waters triggers a see-saw in atmospheric pressure between the Eastern and Western Tropical Pacific, called the Southern Oscillation (SO).
Since El Nino and the SO are related, the two terms are often combined into a single phrase, the El Nino-Southern Oscillation (ENSO). A warm ENSO phase signals El Nino and the cold phase, La Nina.
In what may be a ray of hope for the Indian monsoon, the Bureau has joined other agencies in their outlook of a positive phase of the Indian Ocean Dipole (IOD) occuring in June-August. It mimics the El Nino-La Nina phenomena nearer home.
During a positive IOD phase, the western basin of the Indian Ocean warms up relative to the East, and vice versa. The positive phase is known to power the monsoon, irrespective of what happens in the far-off Pacific. But the Bureau said predictions made at this time of year are less accurate than those made in winter or spring.
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