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Madden–Julian oscillation

Madden–Julian oscillation is a earth science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Madden–Julian oscillation rather than just read about it. In short: The Madden–Julian oscillation (MJO) is the largest element of the intraseasonal (30- to 90-day) variability in the tropical atmosphere. It was discovered in 1971 by Roland Madden and Paul Julian of the American National Center for Atmospheric Research (NCAR).

Madden–Julian oscillation — main illustration
Madden–Julian oscillation — illustration

Key takeaways

  • Madden–Julian oscillation belongs to earth science; place it in that map before memorising details.
  • Learn the definition first, then one example that makes the definition concrete.
  • Connect Madden–Julian oscillation to a quantity you can measure, compute or draw — that is where exam questions come from.
  • Reproduce the core statement of Madden–Julian oscillation from memory before moving on to harder problems.

Reference excerpt

The Madden–Julian oscillation (MJO) is the largest element of the intraseasonal (30- to 90-day) variability in the tropical atmosphere. It was discovered in 1971 by Roland Madden and Paul Julian of the American National Center for Atmospheric Research (NCAR). It is a large-scale coupling between atmospheric circulation and tropical deep atmospheric convection. Unlike a standing pattern like the El Niño–Southern Oscillation (ENSO), the Madden–Julian oscillation is a traveling pattern that propagates eastward, at approximately 4 to 8 m/s (14 to 29 km/h; 9 to 18 mph), through the atmosphere above the warm parts of the Indian and Pacific oceans. This overall circulation pattern manifests itself most clearly as anomalous rainfall. The Madden–Julian oscillation is characterized by an eastward progression of large regions of both enhanced and suppressed tropical rainfall, observed mainly over the Indian and Pacific Ocean. The anomalous rainfall is usually first evident over the western Indian Ocean, and remains evident as it propagates over the very warm ocean waters of the western and central tropical Pacific. This pattern of tropical rainfall generally becomes nondescript as it moves over the primarily cooler ocean waters of the eastern Pacific, but reappears when passing over the warmer waters over the Pacific Coast of Central America. The pattern may also occasionally reappear at low amplitude over the tropical Atlantic and higher amplitude over the Indian Ocean. The wet phase of enhanced convection and precipitation is followed by a dry phase where thunderstorm activity is suppressed. Each cycle lasts approximately 30–60 days. Because of this pattern, the Madden–Julian oscillation is also known as the 30- to 60-day oscillation, 30- to 60-day wave, or intraseasonal oscillation.

Behavior

Distinct patterns of lower-level and upper-level atmospheric circulation anomalies accompany the MJO-related pattern of enhanced or decreased tropical rainfall across the tropics. These circulation features extend around the globe and are not confined to only the eastern hemisphere. The Madden–Julian oscillation moves eastward at between 4 m/s (14 km/h, 9 mph) and 8 m/s (29 km/h, 18 mph) across the tropics, crossing the Earth's tropics in 30 to 60 days—with the active phase of the MJO tracked by the degree of outgoing long wave radiation, which is measured by infrared-sensing geostationary weather satellites. The lower the amount of outgoing longwave radiation, the stronger the thunderstorm complexes, or convection, is within that region. Enhanced surface (upper-level) westerly winds occur near the west (east) side of the active convection. Ocean currents, up to 100 metres (330 ft) in depth from the ocean surface, follow in phase with the east-wind component of the surface winds. In advance, or to the east, of the MJO enhanced activity, winds aloft are westerly. In its wake, or to the west of the enhanced rainfall area, winds aloft are easterly. These wind changes aloft are due to the divergence present over the active thunderstorms during the enhanced phase. Its direct influence can be tracked poleward as far as 30 degrees latitude from the equator in both northern and southern hemispheres, propagating outward from its origin near the equator at around 1 degree latitude, or 111 kilometres (69 mi), per day.

Phases and monitoring The MJO is classified into eight phases depending on the location of enhanced precipitation along the Equator:

Phases 8 and 1: Western Hemisphere and Africa Phases 2 and 3: Indian Ocean Phases 4 and 5: Maritime Continent Phases 6 and 7: Western Pacific The position and strength of the MJO is determined by the Real-time Multivariate MJO (RMM) index, which takes into account the equatorial distribution of outgoing longwave radiation and the zonal winds at low (850 hPa) and high (200 hPa) altitudes.

Irregularities The MJO's movement around the globe can occasionally slow or stall during the Northern Hemisphere summer and early autumn, leading to consistently enhanced rainfall for one side of the globe and consistently depressed rainfall for the other side. This can also happen early in the year. The MJO can also go quiet for a period of time, which leads to non-anomalous storm activity in each region of the globe.

Local effects

Connection to the monsoon

During the Northern Hemisphere summer season the MJO-related effects on the Indian and West African summer monsoon are well documented. MJO-related effects on the North American summer monsoon also occur, though they are relatively weaker. MJO-related impacts on the North American summer precipitation patterns are strongly linked to meridional (i.e. north–south) adjustments of the precipitation pattern in the eastern tropical Pacific. A strong relationship between the leading mode of intraseasonal variability of the North American Monsoon System, the MJO and the points of origin of tropical cyclones is also present. A period of warming sea surface temperatures is found five to ten days prior to a strengthening of MJO-related precipitation across southern Asia. A break in the Asian monsoon, normally during the month of July, has been attributed to the Madden–Julian oscillation after its enhanced phase moves off to the east of the region into the open tropical Pacific Ocean.

Influence on tropical cyclogenesis

… excerpt ends here. Continue reading the full article.

Illustrations

Madden–Julian oscillation: A Hovmöller diagram of the 5-day running mean of outgoing longwave radiation showing the MJO. Time increases from top to bottom in the figure, so contours that are oriented from upper-left to lower-right represent movement from west to east.
A Hovmöller diagram of the 5-day running mean of outgoing longwave radiation showing the MJO. Time increases from top to bottom in the figure, so contours that are oriented from upper-left to lower-right represent movement from west to east.
Madden–Julian oscillation: The structure of the MJO for a period when the enhanced convective phase is centered across the Indian Ocean and the suppressed convective phase is centered over the west-central Pacific Ocean
The structure of the MJO for a period when the enhanced convective phase is centered across the Indian Ocean and the suppressed convective phase is centered over the west-central Pacific Ocean
Madden–Julian oscillation: Onset dates and prevailing wind currents of the southwest summer monsoon in India.
Onset dates and prevailing wind currents of the southwest summer monsoon in India.
Madden–Julian oscillation: The Pineapple Express, an MJO effect on North American weather patterns.
The Pineapple Express, an MJO effect on North American weather patterns.

Worked examples

Example 1 — a first encounter with Madden–Julian oscillation

Start with the simplest possible case. Write down what Madden–Julian oscillation claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In earth science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Madden–Julian oscillation before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Madden–Julian oscillation ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Madden–Julian oscillation

In research
Madden–Julian oscillation appears in earth science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry
Engineering practice reuses Madden–Julian oscillation in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom
Madden–Julian oscillation is common in secondary-school and first-year university syllabi. It links to neighbouring topics Atmospheric dynamics, Climate oscillations, Tropical meteorology, so understanding it makes those chapters shorter.
In everyday life
Look for Madden–Julian oscillation outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.
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How to study Madden–Julian oscillation in 20 minutes

  1. Read the reference excerpt below once, without taking notes.
  2. Close the page and write down what Madden–Julian oscillation means in your own words.
  3. Compare your version with the excerpt and mark what you missed.
  4. Work through the three examples above with pen and paper.
  5. Explain Madden–Julian oscillation out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Madden–Julian oscillation in simple terms?

The Madden–Julian oscillation (MJO) is the largest element of the intraseasonal (30- to 90-day) variability in the tropical atmosphere. It was discovered in 1971 by Roland Madden and Paul Julian of the American National Center for Atmospheric Research (NCAR).

Why does Madden–Julian oscillation matter?

Because it connects several earth science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Madden–Julian oscillation?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Madden–Julian oscillation.

Tags

  • Atmospheric dynamics
  • Climate oscillations
  • Tropical meteorology

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