The Usual Suspect: What is El Niño?
El Niño, which means 'the boy child' in Spanish, refers to the large-scale, abnormal warming of the surface waters in the central and eastern Pacific Ocean. This warming disrupts global atmospheric patterns. In a typical year, a circulation pattern called
the Walker Circulation pushes warm, moist air towards the Indian subcontinent, fueling the monsoon. During an El Niño event, this atmospheric engine shifts eastward, away from India. This can lead to weaker trade winds, reduced moisture transport, and ultimately, a suppression of monsoon rainfall over large parts of the country. Historically, many of India's most severe droughts have occurred in El Niño years.
The Local Hero: The Indian Ocean Dipole (IOD)
While El Niño is playing out in the vast Pacific, our own backyard has a crucial system called the Indian Ocean Dipole (IOD), sometimes nicknamed the 'Indian El Niño'. The IOD is about the temperature difference between the western Arabian Sea and the eastern Indian Ocean near Indonesia. It has three phases: positive, negative, and neutral. In a 'positive' IOD phase, the western Indian Ocean becomes warmer than the east. This warmer water boosts evaporation, pulling moisture-laden winds towards the Indian mainland and enhancing monsoon rains, particularly in the latter half of the season. A strong positive IOD can act as a powerful counter-force, partially offsetting the negative impact of an El Niño, as was seen in years like 1997 and 2019.
The Wild Card: Madden-Julian Oscillation (MJO)
If El Niño is a long-term influence and the IOD is a seasonal one, think of the Madden-Julian Oscillation (MJO) as the unpredictable wild card. The MJO is a massive, eastward-moving pulse of clouds, wind, and rainfall that circles the equator every 30 to 60 days. Unlike El Niño, which sets a background condition for the whole season, the MJO is a transient feature. When the active, rainy phase of the MJO passes over the Indian Ocean, it can trigger intense bursts of rainfall and even help with the timely onset of the monsoon. Conversely, its suppressed phase can lead to dry spells or 'breaks' in the monsoon. A favourably-timed MJO can bring significant rain even in a year when the broader conditions look unfavorable.
A Tug-of-War in the Atmosphere
The Indian monsoon is best understood as a result of a climatic tug-of-war. El Niño in the Pacific pulls moisture away from India, weakening the monsoon. A positive IOD, centered in the Indian Ocean, pulls moisture towards India, strengthening it. Meanwhile, the MJO makes its journey, acting as a powerful but short-term force that can either amplify or dampen rainfall at different times during the season. The final outcome—whether India receives deficient, normal, or surplus rain—depends on which of these forces dominates and when. A strong El Niño can be overwhelming, but if it is met by a strong positive IOD, the monsoon can be saved from complete failure.
Other Influencers in the System
Beyond these three major players, other factors also add layers of complexity. The amount of snow cover over the Himalayas and the Eurasian landmass can influence the temperature contrast that drives monsoon winds. High snow cover tends to weaken the monsoon. The positioning of jet streams—strong winds high in the atmosphere—also plays a role in guiding weather systems. Even the Tibetan Plateau, by acting as a massive elevated heat source in the summer, helps establish the low-pressure system that is fundamental to the monsoon's mechanism. All these elements work in concert, making the monsoon a dynamic system that is more than just a reaction to El Niño.
