Understanding the Indian Monsoon: How ENSO, the Indian Ocean Dipole and the MJO Interact

Why does the Indian summer monsoon behave differently from one year to another? A new study explores how interactions between the Pacific and Indian Oceans, together with the Madden–Julian Oscillation, shape monsoon rainfall across India.

The Indian summer monsoon is one of the most important components of India's climate system. It supplies a major share of the country's annual rainfall and supports agriculture, water resources, ecosystems and livelihoods. However, monsoon rainfall varies considerably from year to year, and even within a single season, different parts of India can experience contrasting rainfall conditions.

Several large-scale climate phenomena influence this variability. Among the most important are the El Niño–Southern Oscillation (ENSO), the Indian Ocean Dipole (IOD) and the Madden–Julian Oscillation (MJO). Although each of these phenomena has been studied extensively, understanding how they interact and jointly influence monsoon rainfall remains an important scientific challenge.

A recent research paper, “Multiscale ENSO–IOD–MJO Interactions Modulating Indian Summer Monsoon Rainfall Variability,” investigates these connections using observational and reanalysis datasets covering the period 1975–2025.

The study examines how different combinations of ENSO and IOD conditions influence seasonal rainfall, atmospheric circulation and MJO activity, as well as how rainfall associated with individual MJO phases varies under different oceanic backgrounds.

Classification of monsoon years from 1975 to 2025 into nine categories based on El Niño, La Niña or neutral ENSO conditions and positive, negative or neutral Indian Ocean Dipole conditions.

Figure 1. Classification of monsoon years (1975–2025) into nine combined ENSO–IOD categories, showing the number of years and relative occurrence of IOD phases. [Source: Ratna et al. (2026), https://doi.org/10.54302/mausam.v77i4.7811]


Three important drivers of monsoon variability

(i) El Niño–Southern Oscillation (ENSO)

ENSO is a coupled ocean–atmosphere phenomenon over the tropical Pacific Ocean. It has three broad phases: El Niño, La Niña and neutral conditions.

El Niño is generally associated with a weakening of the Indian summer monsoon, whereas La Niña often favours stronger monsoon rainfall. However, these relationships are not uniform in every year. The strength and spatial structure of Pacific Ocean warming or cooling, along with other climate influences, can modify the monsoon response.

(ii) Indian Ocean Dipole (IOD)

The IOD represents variations in sea surface temperatures between the western and eastern equatorial Indian Ocean.

A positive IOD occurs when the western Indian Ocean is warmer than the eastern Indian Ocean relative to normal conditions, while a negative IOD represents the opposite pattern.

The IOD can influence atmospheric circulation and rainfall over the Indian region. Importantly, its phase does not always correspond directly to the prevailing ENSO phase. Consequently, the Indian Ocean can modify the influence of Pacific Ocean conditions on the monsoon.

(iii) Madden–Julian Oscillation (MJO)

Unlike ENSO and the IOD, which primarily characterize interannual ocean–atmosphere variability, the MJO is an intraseasonal phenomenon involving large-scale tropical convection and atmospheric circulation.

The MJO typically evolves over a period of several weeks and propagates eastward through the tropics. Its evolution is represented by eight phases, corresponding to different geographical locations of its large-scale convective and circulation patterns.

As the MJO progresses through these phases, its influence on rainfall over India changes. However, the rainfall response associated with a particular MJO phase may also depend on the prevailing ENSO and IOD conditions.

The central question of this study is therefore: Does the same MJO phase produce a similar rainfall response under different ENSO–IOD backgrounds?

How was the study conducted?

The study analysed the period 1975–2025 using sea surface temperature data, gridded rainfall observations, atmospheric reanalysis and daily MJO indices. Monsoon years were classified into nine categories by combining the three ENSO phases—El Niño, La Niña and neutral—with the three IOD phases—positive, negative and neutral. The analysis examined:

  • The seasonal evolution and spatial patterns of tropical sea surface temperature anomalies.

  • Seasonal monsoon rainfall over India and its four homogeneous rainfall regions.

  • Associated atmospheric circulation, including low-level winds and mid-tropospheric vertical motion.

  • MJO amplitude and the frequency of active MJO days across its eight phases.

  • Rainfall anomalies associated with individual MJO phases under different ENSO–IOD conditions.

This integrated approach makes it possible to examine monsoon variability across interannual and intraseasonal timescales within a common framework.


Composite sea surface temperature anomalies during June–September and September–November for nine ENSO–IOD categories from 1975 to 2025, highlighting Pacific and Indian Ocean temperature patterns.

Figure 2: Composite sea surface temperature anomalies during the June–September and September–November seasons for the combined ENSO–IOD categories. Black dots indicate statistically significant anomalies, and rectangles mark the Niño3.4 and Indian Ocean regions used to define the indices. [Source: Ratna et al. (2026), https://doi.org/10.54302/mausam.v77i4.7811]

What are the major findings?

1. The combined state of the Pacific and Indian Oceans matters

The analysis shows that seasonal monsoon rainfall cannot be adequately understood from ENSO alone. The accompanying IOD phase substantially modifies the magnitude and regional distribution of rainfall anomalies over India. For example, La Niña accompanied by a negative IOD produces the strongest positive rainfall anomalies among the categories examined. These wet conditions are associated with strengthened monsoon circulation and enhanced upward motion in the atmosphere. The findings highlight the importance of considering the Pacific and Indian Oceans together when interpreting seasonal monsoon variability.

2. El Niño patterns differ under different IOD conditions

An interesting result concerns the spatial structure of El Niño. El Niño accompanied by a positive IOD predominantly exhibits an Eastern Pacific-like El Niño pattern, whereas El Niño under neutral IOD conditions displays a Central Pacific-like structure. These differences in the tropical sea surface temperature background are accompanied by contrasting atmospheric circulation and rainfall responses over India. This finding emphasizes that not all El Niño events have the same oceanic structure or necessarily produce identical monsoon outcomes.

3. MJO activity varies with the ENSO–IOD background

The study finds systematic differences in MJO amplitude and phase occupancy across the ENSO–IOD categories. La Niña accompanied by a negative IOD shows enhanced MJO phase occupancy during Phases 1–2, while El Niño accompanied by a positive IOD exhibits stronger MJO activity during Phases 5–6, corresponding to the Maritime Continent and western Pacific sectors. These results suggest that the background oceanic state is associated with differences in how active MJO days are distributed across the eight phases.

4. The rainfall response to the MJO depends on the oceanic background

Perhaps the most important finding is that the rainfall response associated with individual MJO phases varies substantially under different ENSO–IOD conditions. Under El Niño accompanied by a positive IOD, rainfall enhancement is observed during MJO Phases 5–6, followed by widespread rainfall suppression during Phases 7–8. In contrast, La Niña accompanied by a negative IOD exhibits the strongest and most coherent rainfall enhancement during Phases 4–5. The regional analysis further reveals that these responses are not spatially uniform. All-India rainfall and the four homogeneous rainfall regions—North India, Central India, East India and the South Peninsula—can respond differently during the same MJO phase.

This is a key message of the study: the rainfall response associated with a particular MJO phase depends on the prevailing ENSO–IOD background and varies across regions.

Consequently, the MJO phase alone may not provide a complete explanation of intraseasonal monsoon rainfall variability.


Standardized Indian monsoon rainfall anomalies across All India and four homogeneous regions for eight MJO phases under six ENSO–IOD background conditions, showing contrasting regional rainfall responses.

Figure 3: Standardized June–September rainfall anomalies across All India and the North, Central, East and South Peninsula regions for eight MJO phases under six ENSO–IOD background conditions. [Source: Ratna et al. (2026), https://doi.org/10.54302/mausam.v77i4.7811]

Why are these findings important?

The Indian summer monsoon is influenced by processes operating across different timescales. ENSO and the IOD characterize important aspects of the interannual oceanic background, while the MJO contributes to the evolution of tropical convection and rainfall on intraseasonal timescales. The study brings these influences together to demonstrate that their combined state is associated with substantial differences in seasonal rainfall, atmospheric circulation, MJO characteristics and phase-dependent rainfall anomalies. This has important implications for understanding why apparently similar large-scale climate conditions may produce different rainfall outcomes in different years.

From an operational perspective, the findings provide a scientific basis for further investigating whether information on ENSO structure, IOD phase and MJO activity can add value to seasonal and subseasonal monsoon prediction. However, the present study focuses on observed relationships and associated atmospheric conditions; it does not directly evaluate improvements in forecast skill. Further research using longer observational records, climate-model ensembles and process-based diagnostics would help clarify the physical mechanisms behind these relationships and assess their potential predictive value.

Read the full research paper

The detailed methodology, figures, regional rainfall patterns and statistical analyses are presented in the following peer-reviewed research article:

Multiscale ENSO–IOD–MJO Interactions Modulating Indian Summer Monsoon Rainfall Variability

Authors: Satyaban B. Ratna, Tanu Sharma, Neha Rani and Mrutyunjay Mohapatra.

Published in Mausam, Volume 77, Issue 4 (October 2026), as part of the Special Issue on the WMO 8th International Workshop on Monsoon (IWM-8), Part 1.

Read the full paper free of charge:

https://doi.org/10.54302/mausam.v77i4.7811

Concluding remarks

Understanding monsoon rainfall requires looking beyond individual climate drivers. The combined influence of ENSO, the IOD and the MJO offers a more comprehensive perspective on why monsoon rainfall varies between years, evolves within a season and differs across regions of India. The findings reinforce the need for a multiscale approach to monsoon research—one that connects the large-scale oceanic background with atmospheric circulation, intraseasonal variability and regional rainfall responses. Understanding these interactions is an important step towards improving our scientific understanding of the Indian summer monsoon and exploring new opportunities for climate prediction.

Related Publications:

Ratna, S. B., C.T. Sabeerali, Tanu Sharma, D.S. Pai, M. Mohapatra, 2024: Combined influence of El Niño, IOD and MJO on the Indian Summer Monsoon Rainfall: Case Study for the years 1997 and 2015, Atmospheric Research, 299, 107214, https://doi.org/10.1016/j.atmosres.2023.107214

Musale, M., Sharma, T., Ratna, S. B., C. T. Sabeerali, P. Rohini, A. Bandgar, O. P. Sreejith and K. S. Hosalikar, (2024): Triple-dip La Niña (2020-2022) and its impact on Indian Summer Monsoon Rainfall: Insight from the Monsoon Mission Coupled Forecasting System, Mausam, 75,3, 769–782, https://doi.org/10.54302/mausam.v75i3.6283

Sharma, Tanu, Satyaban B. Ratna, D.S. Pai, Arti Bandgar, M. Rajeevan, M. Mohapatra, O.P. Sreejith, K.S. Hosalikar, 2024: Indian Summer Monsoon Rainfall Response to Two Distinct Evolutions of La Niña Events, International Journal of Climatology, 44 (12), https://doi.org/10.1002/joc.8588

Pagire, A., Satyban B Ratna, Annalisa Cherchi, S. D. Sanap, OP Sreejith (2025): ENSO-MJO interaction and its association with monsoon extreme rainfall events over the Indian region, International Journal of Climatology, https://doi.org/10.1002/joc.70093

Srinivasan, L., T. Sharma, Satyaban B. Ratna, M. Mohapatra, J. Takle and M. Musale (2026): Why Indian Summer Monsoon Fails despite La Niña Conditions: Role of Madden-Julian Oscillation Phase Persistence, Frontiers in Climate. https://doi.org/10.3389/fclim.2026.1825496 

Ratna, Satyaban B., Sharma, T., Rani, N., Mohapatra, M. (2026): Multiscale ENSO–IOD–MJO Interactions Modulating Indian Summer Monsoon Rainfall Variability, MAUSAM, 77(4), 1201–1222. https://doi.org/10.54302/mausam.v77i4.7811

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