The impact of El Nino always remained a matter of concern, as it squeezes the seasonal rainfall. Of course, degree of adversity vary anything between ‘below normal’ and ‘drought’. Occasionally, it does spare the Indian sub-continent from its unpropitious impact, as it happened in 1997. Notwithstanding, it continues to be the most powerful fluctuation in the climate pattern, across the globe.
ENSO: El Nino conditions in the central-eastern equatorial Pacific have strengthened further. Ocean and atmospheric coupling is fairly strong and the respective variables are consistent with a moderate El Nino event. Almost all the models forecast continuation of the EL Nino event well up to winters of Northern Hemisphere, extendable to early spring of 2024. Subsequent weakening may ultimately turn ENSO-neutral before the next monsoon season.
Entire Nino region remains much warmer than the average. Nino 3.4, the principal indicator for predicting El Nino has reached an all time high of +1.7°C, since March 2016. The negative phase of Southern Oscillation Index (SOI) is complimenting El Nino, as is usually observed. Negative SOI refers to the situation when abnormally high air pressure covers Indonesia and the western tropical Pacific and abnormally low air pressure covers the eastern tropical Pacific.
IOD : A positive Indian Ocean Dipole is on its way. As expected, the index is growing in magnitude and its weekly value is +1.45°C, as on 24September 2023, the highest since October 2019. This is the 6th week above the positive threshold ( +0.4°C). All models predict the positive IOD to persist , at least till end of the year. A moderately positive IOD timely emerged to mitigate harsh impact of El Nino decimating core monsoon month August and acting saviour for September.
MJO : Unlike a standing pattern like ENSO or IOD, the MJO is a travelling pattern that propagates eastward at approximately 4-8m/s, through the atmosphere, above the warm parts of the Indian and Pacific Oceans. The overall circulation pattern manifests itself most clearly as anomalous rainfall. The Madden Julian Oscillation is currently weak and nearly indiscernible. There is no consensus among the numerical models regarding its track and strength , in the next 2 weeks. Possibly, the MJO will meander over the Maritime Continent and Western Pacific with minimal amplitude, over the coming fortnight. The current positioning of index may marginally help to sustain the monsoon activity over the Indian seas, more so for Bay of Bengal.
ENSO is a naturally occurring phenomenon. Under the warmer envelop of lower atmosphere and ocean, these events may become extreme in future. El Nino can bring increased rainfall to southern South America and the Horn of Africa and severe drought to Australia, Indonesia and parts of Southern Asia including India. Courtesy, positive IOD, evolving ‘just in time’, Indian monsoon could get off with a marginal damage. Curtains are drawn with season 2023, yet again, ending ‘below normal’.