Why is the Indian Ocean Dipole in the news

With a "Super El Niño" now forecast for 2026, meteorologists have raised a key open question: whether the Indian Ocean Dipole (IOD) could recur in a positive...

What Happened

With a "Super El Niño" now forecast for 2026, meteorologists have raised a key open question: whether the Indian Ocean Dipole (IOD) could recur in a positive phase, as it did in 1997, and offset the suppressive effect on Indian monsoon rainfall.
In 1997, despite the strongest El Niño of the 20th century (SST anomalies of +2.5°C), India recorded near-normal to above-average monsoon rainfall — widely attributed to a concurrent strong positive IOD event.
A concurrent strong positive IOD in 2026 could again neutralise El Niño's adverse impact on the South-West Monsoon; the absence of such a positive IOD would leave India exposed to significant rainfall deficit.
The IOD is currently being closely tracked by the India Meteorological Department (IMD) and international climate agencies as the most critical modifying factor for the 2026 monsoon season.
Current forecasts do not yet confirm the phase or intensity of the IOD for mid-2026, making long-range monsoon prediction uncertain.

Static Topic Bridges

Indian Ocean Dipole (IOD): Definition and Mechanism

The Indian Ocean Dipole (IOD), sometimes called the "Indian Niño," is a coupled ocean-atmosphere phenomenon in the tropical Indian Ocean analogous to ENSO in the Pacific. It is defined by the difference in sea surface temperatures (SSTs) between two poles: the western pole (off the East African coast, approximately 50°E–70°E, 10°S–10°N) and the eastern pole (off the Indonesian coast/eastern Indian Ocean, approximately 90°E–110°E, 10°S–0°N). When the western Indian Ocean is warmer than average and the eastern Indian Ocean is cooler than average, the IOD is in a "positive phase." The reverse configuration constitutes a "negative phase." IOD events typically develop during the boreal summer (June–August) and peak in October–November, before rapidly decaying in December as the seasonal monsoon circulation breaks down.

Term coined and first described by scientists Saji et al. in a landmark paper published in Nature in 1999.
Measured using the Dipole Mode Index (DMI) — the SST anomaly difference between the western pole (50°E–70°E, 10°S–10°N) and eastern pole (90°E–110°E, 10°S–0°N).
DMI > +0.4°C sustained for at least 3 months = positive IOD; DMI < −0.4°C = negative IOD.
The 1997 positive IOD is considered among the strongest on record.
IOD phases are monitored by IMD, BoM (Australia), JAMSTEC (Japan), and Copernicus.

Connection to this news: The 2026 monsoon season's fate depends critically on whether a positive IOD develops simultaneously with the super El Niño — as occurred in 1997 — or whether El Niño dominates unopposed.

Positive vs. Negative IOD: Impact on Indian Monsoon

A positive IOD creates warmer-than-usual sea surface temperatures in the western Indian Ocean (near the Arabian Sea) and cooler conditions in the eastern Indian Ocean (near Indonesia). This differential warming enhances moisture-laden winds flowing toward the Indian subcontinent, reinforcing the monsoon current and increasing rainfall over India — especially central and peninsular India. Additionally, a positive IOD weakens the subsidence (sinking air) that El Niño induces over the subcontinent, partially or fully neutralising the El Niño drought signal. A negative IOD has the opposite effect: it reinforces El Niño's suppressive effect, amplifying drought risk and increasing cyclogenesis in the Bay of Bengal.

Positive IOD years associated with above-normal Indian monsoon rainfall: 1994, 1997, 2007, 2019.
Negative IOD + El Niño combination: historically associated with severe droughts and below-normal monsoon (e.g., 2015–16 combination contributed to widespread drought in 2015).
In 2019, a strong positive IOD (+2.0 DMI) co-occurred with El Niño Modoki, yet India recorded above-normal monsoon rainfall.
Positive IOD also increases Arabian Sea cyclone frequency, while negative IOD strengthens Bay of Bengal cyclogenesis.
IOD is independent of ENSO but can co-occur with it; the interaction is the key determinant of Indian monsoon outcomes.

Connection to this news: Meteorologists are specifically asking whether the 1997 scenario — strong El Niño offset by strong positive IOD — could repeat in 2026. If it does, India may escape severe monsoon disruption despite the super El Niño.

The 1997 Precedent: El Niño Offset by Positive IOD

The 1997–98 El Niño was the strongest of the 20th century, with SSTs in the Niño 3.4 region peaking at +2.5°C above average — yet India recorded near-normal monsoon rainfall in 1997. Subsequent scientific analysis revealed that an unusually strong concurrent positive IOD altered the local Hadley circulation over the Indian Ocean and the Walker Circulation's response. The IOD-induced anomalous convergence over the Bay of Bengal neutralised the ENSO-induced anomalous subsidence, maintaining normal monsoon convection. This episode is now a benchmark case study in Indian climate science, demonstrating that ENSO is not the sole determinant of Indian monsoon performance.

1997–98 El Niño: SST anomaly peaked at ~+2.5°C — strongest recorded in the 20th century until 2015 equalled it.
Despite strongest El Niño, India 1997 monsoon rainfall was ~102% of Long Period Average (LPA) — above normal.
Mechanism: positive IOD-induced convergence over Bay of Bengal cancelled ENSO-induced subsidence.
The interaction is described in climate science literature as the "ENSO-IOD tug-of-war."
IMD incorporates both ENSO and IOD indices in its long-range monsoon forecast models.

Connection to this news: The 1997 precedent is the direct historical analogy being invoked in 2026 — if a similarly strong positive IOD develops, India could again record adequate monsoon rainfall despite the super El Niño.

South-West Monsoon and Its Governing Mechanisms

The South-West Monsoon (June–September) is the primary rainfall system of India, delivering approximately 75% of the country's total annual precipitation. It originates from the Mascarene High (a semi-permanent subtropical high-pressure belt near Mauritius in the South Indian Ocean), with cross-equatorial flow directed by the Somali Jet and the Inter-Tropical Convergence Zone (ITCZ). The monsoon's temporal and spatial distribution over India is influenced by: (1) land-sea temperature differential between the Indian landmass and the Indian Ocean; (2) ENSO phase (El Niño suppresses, La Niña enhances); (3) IOD phase (positive enhances, negative suppresses); (4) the Eurasian snow cover (heavier snow = weaker monsoon onset); and (5) the Madden–Julian Oscillation (MJO), which modulates active and break monsoon spells on 30–60 day cycles.

India's Long Period Average (LPA) rainfall: 880.6 mm over June–September (1971–2020 baseline).
IMD issues five forecasts for the monsoon season: April long-range, May updated long-range, June short-range, and bi-monthly updates.
Mascarene High → Somali Jet → Arabian Sea branch and Bay of Bengal branch are the two main arms of the monsoon.
IMD "normal" monsoon: 96%–104% of LPA; "deficient": below 90% of LPA.
The monsoon contributes to ~14% of India's GDP directly (agriculture) and influences industrial and service sector demand.

Connection to this news: The IOD's phase will determine whether the South-West Monsoon's governing mechanisms are reinforced or disrupted by the 2026 super El Niño, making IOD monitoring a priority for India's agricultural and water security planning.

Key Facts & Data

IOD first described: Saji et al., Nature, 1999
Dipole Mode Index (DMI) threshold: ±0.4°C sustained for 3 months to qualify as positive/negative IOD
1997–98 El Niño peak SST anomaly: +2.5°C (strongest in 20th century)
India's 1997 monsoon rainfall despite strongest El Niño: ~102% of LPA (above normal)
Three confirmed "very strong" El Niño events since 1950: 1982–83, 1997–98, 2015–16
Western IOD pole coordinates: 50°E–70°E, 10°S–10°N (off East Africa)
Eastern IOD pole coordinates: 90°E–110°E, 10°S–0°N (off Indonesia)
India's monsoon LPA: 880.6 mm (June–September, 1971–2020 baseline)
Positive IOD years with above-normal Indian monsoon: 1994, 1997, 2007, 2019
IMD's monsoon forecast incorporates both ENSO indices and DMI as primary predictors
IOD peaks: October–November; decays rapidly in December with reversal of monsoon winds