Madden-Julian Oscillation

Also called: MJO · Topic: Climate of India and the Monsoon · NCERT: Beyond NCERT

Meaning

The Madden-Julian Oscillation (MJO) is a moving pulse of cloud, rain, wind and air pressure. It travels eastward around the tropics and comes back to where it started every 30–60 days [2]. It matters because it controls when India gets heavy rain and when it gets dry gaps within one monsoon season. It is also the main basis for IMD's week-by-week forecasts [1].

Explanation

What it is and how it is built

• Who described it: Madden and Julian, in 1971-72.
• Intraseasonal: the MJO changes within a single season. ENSO and IOD are different, because they last for months.
• Two parts that move together [2]:
• A wet area. Air rises here, clouds build up and rain becomes stronger.

• A dry area behind it. Air sinks here, the sky stays clear and rain is weaker.

• Both parts drift east, mainly over the Indian and Pacific Oceans [2].

• Speed: about 5 m/s [3].
• How it is measured: the MJO has no single index number like Niño 3.4 or the DMI. It is described by two things:
• Phase: where the wet area is now.
• Amplitude: how strong it is.

How it works over India (cause → process → result)

• Active (wet) phase over the Indian Ocean
• More air rises and there is more convection (warm, moist air rising to form clouds).
• Result: active monsoon spells with heavy rain.
• It can trigger monsoon onset over Kerala.

• It helps form low-pressure systems and cyclones in the Bay of Bengal and the Arabian Sea.

• MJO absent, or its dry phase over India

• Air sinks and few clouds form.
• Result: a break-in-monsoon (a dry gap of days to weeks in the middle of the season).

The Maritime Continent "barrier"

• The Maritime Continent is the group of islands and seas between the Indian and Pacific Oceans, such as Indonesia and the Philippines.
• As the MJO passes over this region, it often weakens or dies out [3].
• So not every pulse that forms over the Indian Ocean reaches the Pacific at full strength.

Its place among the monsoon teleconnections

• A teleconnection is a link between the weather in two places that are far apart.
• ENSO and IOD act over months and seasons. They decide whether the whole monsoon is good or bad.
• The MJO acts over weeks. It decides the timing of onset, active spells and breaks within one season [2][3].

Where it occurs

• Across the whole tropics: it moves east around the globe. It is strongest over the Indian Ocean and the Pacific Ocean [2].
• Maritime Continent (Indonesia, Philippines): the MJO often weakens or fades here [3].
• India:
• Kerala: the MJO's active phase can trigger monsoon onset here.
• Bay of Bengal and Arabian Sea: its active phase helps form low-pressure systems and cyclones.

• Across the country during June–September: its phases bring active spells and breaks-in-monsoon.

• Forecast use in India: the IMD (India Meteorological Department) bases its extended range forecasts mainly on the MJO. These are 7-day averaged forecasts for the next four weeks, updated every Thursday [1].

Don't confuse with

• ENSO (El Nino–Southern Oscillation): ENSO sits in the equatorial Pacific, comes every 3-7 years and lasts months. It affects the total rain of the whole season. The MJO moves, repeats every 30–60 days and affects only the timing of wet and dry spells.
• Indian Ocean Dipole (IOD): the IOD is a fixed east–west difference in sea temperature in the tropical Indian Ocean. It is measured by the DMI and peaks around September–November. The MJO does not stay in one place. It is a pulse that travels east around the tropics.
• Break-in-monsoon: this is the result, a dry gap within the season. The MJO is one cause, through its absence or its dry phase over India.
• Trade winds / Walker circulation: these move air east to west along the equator. The MJO moves eastward. Examiners often swap the direction.

Prelims Hooks

• The MJO moves eastward, has a 30–60 day cycle and travels at about 5 m/s [2][3].
• It was described by Madden and Julian (1971-72). It is intraseasonal, not interannual like ENSO.
• Trap: the MJO controls active spells and breaks, not the total rain of the season. The season's total depends mainly on ENSO and IOD [2][3].
• Maritime Continent (Indonesia, Philippines) → the MJO often weakens or dies out here [3].
• MJO index = phase (location) + amplitude (strength). Niño 3.4 and SOI belong to ENSO, and DMI belongs to IOD.
• IMD extended range forecast = 7-day averages for the next four weeks, updated every Thursday, based mainly on the MJO [1].

Mains Points

• Why El Nino does not always mean drought (GS-I):
• El Nino shifts the Walker circulation (the east–west loop of air along the equator), so air sinks over India.
• A well-timed MJO active phase over the Indian Ocean can still bring active spells, help onset over Kerala and form low-pressure systems. A positive IOD (1997, 2019) can also help.

• So forecasting needs many indicators. IMD now uses coupled multi-model ensembles (MME, since 2021) for the season, and MJO-based extended range forecasts for the coming weeks [1].

• Using the MJO for farming and disasters (GS-III):

• A long break-in-monsoon hurts kharif sowing and lowers reservoir storage.
• Four-week forecasts, issued weekly [1], help plan sowing dates, contingency crop plans and water release.

• The MJO's active phase helps cyclones form in the Bay of Bengal and Arabian Sea, so tracking it gives early warning for disaster preparedness.

• Limits and research needs (GS-I/III):

• The MJO often fades over the Maritime Continent [3], which makes its path hard to predict.
• Better ocean observation (INCOIS) and coupled models (Monsoon Mission) can improve forecasts of the timing of onset and breaks.

Related concepts

• Indian Ocean Dipole

Read more

• Teleconnections: El Nino, the Southern Oscillation, the Indian Ocean Dipole and the MJO