MADDEN-JULIAN OSCILLATION
1. Context
After remaining largely inactive for more than a week, the monsoon finally picked some strength and momentum beginning Monday. Maharashtra, for instance, received its first good rainfall of the season on Tuesday.
2. What is the Madden-Julian oscillation?
- The Madden–Julian Oscillation (MJO) is one of the most important atmospheric phenomena in the tropical region of the Earth. It is a large-scale pattern of atmospheric circulation characterized by alternating periods of enhanced and suppressed rainfall that travels eastward around the equator.
- Unlike cyclones, which are localized weather systems, or seasonal climate phenomena such as the El Niño–Southern Oscillation (ENSO), the MJO is an atmospheric disturbance that continuously moves across the tropical oceans, influencing weather conditions over vast geographical areas.
- The phenomenon was first identified in 1971 by meteorologists Roland Madden and Paul Julian, after whom it is named. Their research showed that tropical rainfall and atmospheric pressure exhibit a recurring pattern that moves eastward around the globe over a period of about one to two months.
- The MJO originates most frequently over the tropical Indian Ocean, where warm ocean waters provide the energy necessary for the development of deep convection.
- The system then moves eastward across the maritime continent, including Indonesia, into the tropical Pacific Ocean and, on some occasions, continues into the Atlantic Ocean before gradually weakening. The entire cycle generally takes between 30 and 60 days, although it may sometimes extend to nearly 90 days.
- The MJO consists of two distinct phases: the active (enhanced) phase and the suppressed phase. During the active phase, warm, moist air rises from the Earth's surface, leading to the formation of extensive cloud cover, heavy rainfall, and intense thunderstorm activity.
- This upward movement of air releases large amounts of latent heat, strengthening atmospheric circulation. In contrast, the suppressed phase is characterized by sinking air, which inhibits cloud formation and results in clear skies, reduced rainfall, and relatively dry weather conditions.
- As the MJO moves eastward, these two phases travel together, causing alternating wet and dry periods in tropical regions.
- One of the reasons the MJO is scientifically important is that it serves as a bridge between short-term weather events and long-term climate variability.
- While ordinary weather systems usually last for only a few days, and climate phenomena like ENSO persist for several months or even years, the MJO operates on an intra-seasonal timescale, making it highly valuable for forecasting weather several weeks in advance.
- The MJO has a profound influence on the Indian monsoon. When its active phase is located over the tropical Indian Ocean and surrounding regions, convection increases significantly, leading to enhanced monsoon rainfall over India.
- This often results in active monsoon spells with widespread precipitation. Conversely, when the suppressed phase dominates the region, rainfall decreases, leading to weak or break monsoon conditions.
- Therefore, meteorologists closely monitor the MJO to improve monsoon forecasts and assess the likelihood of heavy rainfall or prolonged dry spells.
- The influence of the MJO is not limited to the Indian monsoon. It also plays a major role in the formation and intensification of tropical cyclones over the Indian Ocean, the Pacific Ocean, and even parts of the Atlantic Ocean.
- During its active phase, the atmosphere becomes more unstable, humidity increases, and vertical wind conditions become more favourable for cyclone development. As a result, periods of increased cyclone activity often coincide with the passage of the active MJO phase.
- Apart from affecting tropical weather, the MJO also influences atmospheric circulation in higher latitudes through a process known as teleconnection.
- Changes in tropical convection caused by the MJO can alter jet stream patterns, influencing winter storms, cold waves, heat waves, and heavy rainfall events in regions far away from the tropics, including North America, Europe, and East Asia. Thus, despite being a tropical phenomenon, its impacts extend across the globe.
- The MJO is often confused with the El Niño–Southern Oscillation, but the two are fundamentally different.
- The MJO is a moving atmospheric disturbance that travels continuously around the globe and lasts only a few weeks to a couple of months. ENSO, on the other hand, is a coupled ocean-atmosphere phenomenon centred over the equatorial Pacific Ocean and typically persists for several months to two years or more.
- While ENSO changes sea surface temperatures significantly, the MJO primarily affects atmospheric circulation and rainfall without producing major long-term changes in ocean temperatures.
- An easy way to understand the MJO is to imagine the tropical atmosphere as a giant circular race track. The active phase of the MJO resembles a moving cluster of rain-bearing clouds that travels steadily around this track, bringing heavy rainfall and thunderstorms wherever it passes.
- Behind this active phase follows the suppressed phase, which brings relatively dry and clear weather. This continuous movement creates alternating periods of wet and dry conditions across tropical regions
3. How does the Madden-Julian oscillation affect India?
- The Madden–Julian Oscillation (MJO) has a significant influence on India's weather, particularly the Southwest Monsoon, tropical cyclones, and extreme rainfall events.
- Since the MJO is a moving region of enhanced and suppressed convection (thunderstorm activity), its position relative to India determines whether the country experiences increased rainfall or dry conditions.
- The MJO usually originates over the tropical Indian Ocean and moves eastward across the maritime continent and the Pacific Ocean. When the active phase of the MJO is located over the Indian Ocean and the region surrounding India, it strengthens the upward movement of warm, moist air.
- This leads to increased cloud formation, widespread thunderstorms, and heavy rainfall over many parts of the country. As a result, the southwest monsoon becomes more vigorous, producing active monsoon conditions and above-normal rainfall.
- On the other hand, when the suppressed phase of the MJO moves over the Indian Ocean, the atmosphere experiences downward movement of air, reducing cloud formation and rainfall.
- During this period, India often witnesses breaks in the monsoon, where rainfall decreases significantly for several days despite the monsoon season being in progress. Such breaks can affect agricultural activities by reducing soil moisture and delaying crop growth.
- The MJO also influences the onset and progress of the southwest monsoon. A strong active MJO phase over the Indian Ocean during late May or early June can support the timely onset and rapid advancement of the monsoon across the Indian subcontinent.
- Conversely, if the active phase is located far away over the Pacific Ocean during this period, the onset may be delayed or the monsoon may initially remain weak.
- Another important impact of the MJO is on extreme rainfall events. When its active phase coincides with other favourable weather systems such as low-pressure areas or monsoon depressions over the Bay of Bengal or the Arabian Sea, rainfall intensity can increase dramatically.
- This may result in widespread flooding, landslides in mountainous regions, and urban flooding in major cities. Many episodes of exceptionally heavy monsoon rainfall in India have been linked to a strong active phase of the MJO.
- The MJO also plays a crucial role in the formation and intensification of tropical cyclones over the Bay of Bengal and the Arabian Sea. During its active phase, the atmosphere becomes more unstable, humidity increases, and vertical wind conditions become more favourable for cyclone development.
- Consequently, the probability of cyclogenesis and cyclone intensification rises when the active MJO is present over the northern Indian Ocean. In contrast, the suppressed phase generally inhibits cyclone formation by creating less favourable atmospheric conditions.
- India's agricultural sector is particularly sensitive to the MJO because agriculture depends heavily on the distribution of monsoon rainfall.
- An active MJO phase can provide beneficial rainfall for crops such as rice, cotton, sugarcane, and pulses. However, if the rainfall becomes excessive, it may damage standing crops through flooding and waterlogging. Similarly, an extended suppressed phase can reduce rainfall, leading to moisture stress and lower agricultural productivity.
- The MJO also affects temperature patterns across India. During the active phase, increased cloud cover and rainfall generally reduce daytime temperatures and provide relief from heat. During the suppressed phase, clear skies allow greater solar heating, often resulting in hotter daytime conditions and, in some seasons, the development of heat waves.
- Meteorologists in India, especially at the India Meteorological Department, closely monitor the MJO because it is one of the most reliable indicators for extended-range weather forecasting.
- Since the MJO evolves over several weeks, it helps forecasters predict active and weak phases of the monsoon, the likelihood of heavy rainfall, and the potential for tropical cyclone formation about two to four weeks in advance.
- This information is valuable for agriculture, water resource management, disaster preparedness, and reservoir operations.
4. What is the difference between Madden-Julian oscillation and ENSO?
- The Madden–Julian Oscillation (MJO) and the El Niño–Southern Oscillation (ENSO) are two of the most important climate phenomena affecting global weather.
- Although both originate in the tropical regions and influence rainfall, temperature, monsoons, and tropical cyclones, they differ significantly in their nature, duration, movement, and impacts.
- Understanding these differences is essential for interpreting weather and climate variations across the world.
- The Madden–Julian Oscillation is primarily an atmospheric phenomenon. It consists of a moving zone of enhanced and suppressed cloud formation and rainfall that travels eastward around the equator.
- The MJO originates over the tropical Indian Ocean and usually moves across the maritime continent, the tropical Pacific Ocean, and sometimes into the Atlantic Ocean. The complete cycle generally takes 30 to 60 days, making it an intra-seasonal weather phenomenon.
- In contrast, ENSO is a coupled ocean-atmosphere phenomenon. It develops due to changes in sea surface temperatures and atmospheric pressure across the equatorial Pacific Ocean. ENSO has three phases: El Niño, La Niña, and the neutral phase.
- Unlike the MJO, ENSO does not move continuously around the globe. Instead, it remains centred over the equatorial Pacific Ocean and influences global climate through changes in ocean temperatures and atmospheric circulation.
- An ENSO event typically lasts 9 to 12 months, although some events may continue for nearly two years.
- Another major difference lies in the timescale. The MJO is a short-term oscillation that affects weather patterns over several weeks. Meteorologists use it to forecast rainfall, tropical cyclones, and monsoon activity two to four weeks in advance.
- ENSO, on the other hand, operates over much longer periods and is used for seasonal climate forecasting, helping predict rainfall and temperature anomalies several months ahead.
- The movement of these two phenomena also differs considerably. The MJO is a travelling disturbance that continuously propagates eastward around the equator.
- Wherever its active phase passes, it enhances cloud formation, thunderstorms, and rainfall, while the following suppressed phase brings drier conditions.
- ENSO does not travel in this manner. Instead, it represents large-scale warming (El Niño) or cooling (La Niña) of the central and eastern equatorial Pacific Ocean, with atmospheric circulation adjusting to these ocean temperature changes.
- The influence of the two systems on the Indian monsoon is also different. A favourable active phase of the MJO over the Indian Ocean can strengthen the southwest monsoon for several weeks, leading to active monsoon spells and heavy rainfall.
- However, once the MJO moves away, its influence diminishes. ENSO affects the overall seasonal strength of the monsoon. During El Niño years, India often experiences weaker monsoon rainfall and an increased likelihood of drought, while La Niña years generally favour stronger monsoon rainfall and wetter-than-normal conditions.
- Although this relationship is not absolute, it remains one of the most important factors influencing India's seasonal rainfall.
- The MJO also has a strong influence on tropical cyclone formation because its active phase creates favourable atmospheric conditions for cyclone development over the Indian Ocean, western Pacific, and other tropical basins.
- ENSO also affects cyclone activity, but mainly by altering ocean temperatures and large-scale wind patterns over an entire cyclone season rather than over a few weeks.
- An important distinction is that the MJO is primarily driven by changes in atmospheric convection, whereas ENSO is driven by interactions between the ocean and the atmosphere, especially variations in sea surface temperatures and trade winds across the Pacific Ocean.
- Although they are different phenomena, the MJO and ENSO can interact with each other. For example, repeated strong MJO events can sometimes influence the evolution of El Niño or La Niña conditions by affecting westerly wind bursts over the Pacific Ocean.
- Similarly, the background conditions created by ENSO can modify the strength and behaviour of the MJO.
5. Why is the Southwest Monsoon critical for Kharif agriculture in India?
- The Southwest Monsoon is the backbone of India's agricultural economy and plays a decisive role in the success of the Kharif cropping season. Kharif crops are sown with the onset of the monsoon, generally during June and July, and harvested between September and October.
- Since a large proportion of India's cultivated land is still dependent on rainfall rather than irrigation, the timing, amount, and distribution of monsoon rainfall directly determine agricultural productivity, food security, and rural livelihoods.
- The southwest monsoon provides nearly 70–75% of India's annual rainfall, making it the primary source of water for agriculture.
- As the monsoon winds reach the Indian subcontinent from the Arabian Sea and the Bay of Bengal, they bring widespread rainfall across most parts of the country.
- This rainfall replenishes soil moisture, enabling farmers to prepare fields and sow Kharif crops such as rice, maize, cotton, soybean, groundnut, millets, pulses, and sugarcane.
- The onset of the southwest monsoon marks the beginning of the Kharif agricultural season.
- A timely arrival allows farmers to sow seeds at the optimum time, ensuring proper germination and healthy crop establishment. If the monsoon is delayed, sowing operations are postponed, shortening the growing season and often reducing crop yields. In severe cases, farmers may have to shift to short-duration or drought-resistant crop varieties.
- Apart from the onset, the distribution of rainfall throughout the season is equally important. Crops require water at different stages of growth, including germination, vegetative growth, flowering, and grain filling.
- Well-distributed rainfall ensures a continuous supply of moisture during these critical stages.
- However, prolonged dry spells or breaks in the monsoon can lead to moisture stress, poor plant growth, and lower productivity.
- Conversely, excessive rainfall within a short period can cause waterlogging, flooding, and root damage, affecting crop health and yield.
- The southwest monsoon is particularly important because nearly half of India's net sown area remains rain-fed, despite significant expansion of irrigation facilities. Farmers in these regions rely almost entirely on monsoon rainfall.
- Consequently, a good monsoon generally leads to higher agricultural production, while a weak or deficient monsoon often results in drought, crop failure, and financial distress among farming communities.
- Monsoon rainfall also replenishes reservoirs, lakes, rivers, ponds, and groundwater aquifers, which provide irrigation water during the later stages of the Kharif season and for the subsequent Rabi cropping season. Adequate reservoir storage ensures sufficient water availability for irrigation, drinking water, hydropower generation, and industrial use throughout the year.
- The performance of the Kharif season has a significant impact on India's food security. Crops such as rice and pulses constitute staple food items for millions of people.
- A successful monsoon leads to higher food grain production, improved food availability, and stable market supplies. In contrast, poor monsoon performance may reduce agricultural output, creating supply shortages and increasing dependence on buffer stocks or imports.
- The southwest monsoon also influences the Indian economy. Agriculture supports a substantial share of the country's population, particularly in rural areas. A normal monsoon generally increases farm incomes, boosts rural demand for goods and services, and supports overall economic growth.
- Conversely, a deficient or erratic monsoon can reduce agricultural income, lower rural consumption, and adversely affect sectors such as fertilizers, farm machinery, consumer goods, and banking.
- The monsoon has an important bearing on inflation, especially food inflation. Good rainfall usually leads to abundant production of cereals, vegetables, fruits, and pulses, helping stabilize food prices. On the other hand, deficient rainfall often reduces agricultural output, leading to higher food prices and contributing to overall inflationary pressures in the economy.
- The southwest monsoon also supports allied activities such as animal husbandry, fisheries, and horticulture. Adequate rainfall improves pasture availability for livestock, replenishes ponds used in inland fisheries, and provides favourable conditions for the cultivation of fruits, vegetables, and plantation crops. Thus, its benefits extend well beyond crop production.
6. Way Forward
An IMD bulletin on Wednesday forecast low to moderate rainfall activity in the areas covered by the monsoon — which is only around half of the country’s landmass. Around this time in June, the monsoon normally covers almost the entire country.
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For Prelims: Indian and World Geography
For Mains: eneral Studies I: Important Geophysical phenomena such as earthquakes, Tsunami, Volcanic activity, cyclone etc
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Previous Year Questions
1.With reference to Ocean Mean Temperature (OMT), which of the following statements is/are correct? (UPSC CSE, 2020)
1. OMT is measured up to a depth of 26ºC isotherm which is 129 meters in the south-western Indian Ocean during January-March. 2. OMT collected during January-March can be used in assessing whether the amount of rainfall in monsoon will be less or more than a certain long-term mean. Select the correct answer using the code given below: (a) 1 only (b) 2 only (c) Both 1 and 2 (d) Neither 1 nor 2 Answer (b)
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Source: Indianexpress
