CLOUDS AND PRECIPITATION

CLOUDS AND PRECIPITATION

A cloud is an accumulation of tiny water droplets and ice crystals suspended in the Earth’s atmosphere. Clouds are essential in the climate system as they reflect sunlight and help cool the planet.

Process of Cloud Formation:

1. Water vapor: Water exists in the air as tiny gas particles, called water vapor.
2. Aerosols: Tiny particles like dust and salt float in the air, known as aerosols.
3. Condensation: When the air cools, water vapor sticks to aerosols, leading to condensation. This forms small droplets around the aerosols.
4. Cloud formation: As these small droplets combine, they grow in size, eventually forming clouds. Clouds are primarily produced through condensation as the air cools and loses its capacity to hold water vapor, resulting in cloud formation.

Causes of Cloud Formation:

There are five primary factors that lead to the rising and cooling of air, which results in cloud formation:

1. Surface heating: When the ground is heated by the sun, it causes the air in contact with it to rise. This rising air, often referred to as thermals, forms cumulus clouds.
2. Topography or orographic forcing: Air is forced to rise over geographic features like mountains or hills. As the air rises, it cools, resulting in cloud formation. Layered clouds are commonly produced in this manner.
3. Frontal: Clouds form when warm air rises over a cold mass of air along fronts. A front is the boundary between two air masses, one warm and moist, and the other cold and dry.
4. Convergence: Air from different directions converges and rises, which can lead to the formation of cumulus clouds and cause showery conditions.
5. Turbulence: Sudden changes in wind speed with altitude create turbulent eddies in the air, contributing to cloud formation.

Importance of Clouds:

1. Regulate energy: Clouds help balance the Earth’s energy by reflecting and scattering solar radiation while absorbing the Earth’s infrared energy.
2. Precipitation: Clouds are essential for precipitation, as they are necessary to condense water vapor into rain or snow.
3. Maintain heat budget:
   • At night: Clouds trap heat and keep temperatures warm by reducing heat loss.
   • During the day: Clouds help keep temperatures cooler by acting as a shield against direct sunlight.
4. Hydrological cycle: Clouds are a critical part of the water cycle, as they facilitate rainfall and snowfall.
5. Weather forecasting: Studying clouds provides valuable data for understanding weather and predicting climatic patterns.

PRECIPITATION

Precipitation occurs when condensed water particles in the air grow large enough to overcome the resistance of air and fall to the ground. This process happens after the continuous condensation of water vapor, and when droplets reach a sufficient size, they are released as rain, snow, or other forms of moisture.

Precipitation Hypothesis – Collision-Coalescence Hypothesis:

1. Assumption: This hypothesis assumes that clouds contain differently sized water droplets.
2. Collision: Water droplets of various sizes collide in the cloud due to convection currents. Small droplets are initially suspended in the cloud until they grow large enough to fall.
3. Coalescence: Larger droplets collide with smaller droplets, causing them to merge and grow in size.
4. Fall down: Eventually, as droplets grow too large to remain suspended, they fall to the ground as precipitation.

Ice Crystal Formation Theory:

1. Assumption: This theory assumes that supercooled water droplets exist in clouds. These droplets remain in liquid form even at temperatures below freezing.
2. Competition for water vapor: Both ice crystals and supercooled water droplets compete for the same available water vapor within the cloud.
3. Ice crystal growth: Ice crystals grow because there is lower vapor pressure around the crystal than around the water droplet. The ice crystal attracts more vapor, which then turns into ice. As this happens, water droplets lose their vapor to the ice crystals, and the ice crystals continue to grow until they are large enough to fall.
4. Crystal becomes larger: As ice crystals fall through the lower and warmer parts of the cloud, they collect additional moisture, growing even larger.
5. Precipitation: These ice crystals may fall as snowflakes or melt into raindrops before reaching the Earth’s surface.

Types of Precipitation/Rainfall:

1. Convectional Rainfall:
   • Air rises: Air heated at the surface becomes lighter and rises in convection currents. As it rises, it cools and condensation occurs, forming cumulus clouds.
   • Release of latent heat: The process releases latent heat of condensation, which forces the air to rise even higher.
   • Characteristics:

• Duration: Convectional precipitation is usually heavy but short in duration.
• Localized: It is highly localized and confined to specific areas.
• Minimum cloudiness: Occurs with minimal cloud cover.
• Form: Often associated with hail and graupel (soft hail).
• Location: Occurs mainly in summer and is common in equatorial regions such as the Congo Basin, Amazon Basin, and islands of Southeast Asia.

1. Frontal and Cyclonic Rainfall:
   • Meeting of different air masses: When two air masses with different temperatures meet, turbulence is created. Along the front where the masses meet, convection occurs and precipitation is generated.
   • Characteristics:

• Front: A front is the boundary that separates two different air masses, which plays a crucial role in the formation of precipitation.
• Duration: The type of rainfall is mainly for a few hours to a few days.
• Location: The Tropic and Temperate Zones receive such rainfall.
• Example: For instance, in north-west Europe, cold continental air and warm oceanic air converge to produce heavy rainfall in adjacent areas.

1. Orographic Rainfall:

• Uplift of air: Wind forces moist air to rise as it moves towards mountainous terrain. The mountain forces the air to ascend further, leading it to cool and condense.
• Precipitation process: Once the air cools as it rises, condensation occurs, and the air undergoes precipitation.
• Formation of thick clouds: The rising air mass becomes unstable, forming large, dense clouds. As these clouds move upward, they further condense into droplets and fall as raindrops.
• Characteristics:
• Heavy rainfall on the windward side: Orographic rainfall is primarily seen on the windward side of mountains where moist air is forced upward, causing heavy rain.
• Rain shadow region: The leeward side (opposite side of the mountain) is often dry and may receive little to no rainfall, forming a rain shadow area.
• Mountains as barriers: Mountains act as barriers that force moist air to rise, resulting in this type of rainfall.
• Location: This type of rainfall is observed in mountainous and hilly regions.
• Example: Mahabaleshwar (on the windward side of the Western Ghats) receives over 600 cm of rainfall, whereas Pune (in the rain shadow) receives only about 70 cm.

CLOUD SEEDING

Cloud seeding is an artificial method used to induce moisture in clouds and cause rainfall. This is done by spreading substances like dry ice or silver iodide aerosols into the upper parts of clouds.

• Current Example: The UAE’s National Center of Meteorology has employed cloud seeding to mitigate extreme weather conditions.

Methods of Cloud Seeding:

1. Hygroscopic cloud seeding: Involves dispersing salts (through flares or explosives) into lower portions of clouds. These salts grow as they absorb moisture.
2. Static cloud seeding: Uses chemicals like silver iodide, which form crystals around which moisture condenses.
3. Dynamic cloud seeding: Boosts vertical air currents, causing more water to pass through clouds, ultimately leading to increased rainfall.

Applications of Cloud Seeding:

1. Environmental:
   • Water Pollution Control: Cloud seeding can help maintain minimum river flows and dilute the effects of treated wastewater discharges from industries and municipalities.
   • Tackle Air Pollution: Cloud seeding can potentially be used to settle down toxic air pollutants through the rain.
     • For Example: Recently, Central Pollution Control Board along with other researchers were mulling use of cloud seeding to tackle Delhi’s air pollution.

1. Economic:
   • Boosting the Economy: By creating rain, cloud seeding can enhance agricultural productivity, especially in drought-affected areas, supporting local economies.
     • Example: Project Varshadhari in Karnataka in 2017 aimed at aiding drought-stricken regions.
   • Agriculture: It creates rain to assist crop production and improve harvests in dry regions.
   • Power Generation: Cloud seeding has been used in places like Tasmania, Australia, to augment water availability for hydroelectric power over the past 40 years.
   • Tourism: Cloud seeding can transform arid or dry areas into more hospitable climates, enhancing tourism opportunities.
2. Geographic:
   • Creation of Rain: It is a useful technique to increase rainfall in regions suffering from water scarcity or drought, enhancing food security and creating a conducive environment for living.
   • Weather Regulation: Cloud seeding can help control adverse weather conditions in specific regions.
     • Example: The Project Sky Water in the USA in 1962 was focused on weather modification, including fog dispersal and hail suppression.
   • Geographically Oriented Uses: It can be utilized in specific locations, such as airports, where it helps create stable weather conditions for flight operations.

Challenges of Cloud Seeding:

1. Use of Potentially Harmful Chemicals: The chemicals used (like silver iodide) may have adverse effects on the environment. Plants could absorb these chemicals, leading to contamination of crops and ecosystems.
2. Expensive Method: Cloud seeding is costly, as it requires planes to disperse the chemicals into the clouds, making it unaffordable for regions lacking financial resources.
3. Abnormal Weather Patterns: Artificially induced rain may disrupt normal weather cycles, potentially causing droughts in regions that normally receive moisture.
4. Pollution: Residual chemicals like silver iodide, dry ice, or salt can have toxic effects on the environment. Additionally, cloud seeding could contribute to greenhouse gas emissions.
5. Dependence on Atmospheric Conditions: Cloud seeding can only be successful under specific atmospheric conditions, which are not always predictable or controllable. For example, the presence of sufficient moisture in the atmosphere is essential.

CLOUDBURST

A cloudburst is a weather phenomenon characterized by an extreme amount of precipitation occurring within a short period in a small geographical area. Cloudbursts typically involve unexpected rainfall exceeding 100 mm/h over an area of around 20-30 square kilometers.

• Current Incident: As an example, around five bodies were recovered, and more than 40 people were reported missing after a cloudburst hit a remote village in Jammu and Kashmir’s Kishtwar district on 28 July 2021.

Occurrence of Cloudbursts:

1. Common in mountains: Although cloudbursts can happen in plains, they are more likely to occur in mountainous regions.
2. Upward movement of air: Cloudbursts occur when saturated clouds are unable to release rain due to the warm air rising rapidly and preventing precipitation.
3. Raindrop gain size: Raindrops are carried upwards by air currents instead of falling, which allows them to gain size.
4. Quick flash: At some point, the raindrops become too heavy to remain suspended and fall together, resulting in a sudden, intense downpour.
5. Maximum relative humidity: Cloudbursts often occur when there is maximum humidity and cloud cover, and slow-moving winds cause a rapid condensation of moisture.
6. No need for cloud clash: It is not necessary for cloudbursts to involve the collision of clouds with solid bodies like mountains. For example, in June 2013, a cloudburst occurred in the Himalayan region when monsoon winds and ascending jet streams resulted in heavy rainfall, causing devastating floods and landslides.

Characteristics of Cloudbursts:

1. Cumulonimbus cloud: Cloudbursts are often associated with cumulonimbus clouds, which are vertical columns formed as air moves upward over hilly terrain.
2. Hilly area most suitable: Hilly terrains are conducive to cloudbursts due to the rising heated air currents.
3. Form: These clouds typically produce rain, thunder, and lightning.
4. Elevation: Cloudbursts usually occur at elevations between 1,000-2,500 meters above sea level.

Impact of Climate Change:

1. Increasing frequency: Several studies suggest that climate change will result in an increased frequency and intensity of cloudbursts in cities across the globe.
2. WMO research: In May 2021, the World Meteorological Organization (WMO) stated that there is approximately a 40% chance of the global temperature temporarily rising by 1.5°C above pre-industrial levels within the next five years. There is also a 90% chance that at least one year between 2021 and 2025 will be the warmest on record, potentially displacing 2016 from the top position.
3. Himalayan region more prone: More cloudbursts are occurring in the Himalayan region because the temperature rise in this area is higher than the global average rate, exacerbating climate issues.

VARIABILITY OF RAINFALL

Rainfall variability refers to the degree to which the amount of rainfall varies over time and across different geographical regions. This is a crucial factor in climatology and is influenced by:

• Natural Factors: These include geographical factors like river basins, pressure belts, wind directions, altitude, and latitude.
• Anthropogenic Factors: These human-influenced factors include deforestation (places with more trees tend to receive more rainfall) and the construction of dams, which can alter rainfall patterns.

Types of Rainfall Variability:

There are two components of rainfall variability: temporal and areal. The image highlights temporal variation, which describes how rainfall varies across seasons.

1. Temporal Variation: Meteorologists recognize four seasons with varying rainfall distribution:

• Cold Weather Season: There is little rainfall during this period in some parts of India. Weak temperate cyclones from the Mediterranean, known as Western Disturbances, can bring rain to parts of northwestern India.
• Hot Weather Season: Sudden contact between dry and moist air masses can lead to local storms and torrential rains.
• Southwest Monsoon Season: Over 80% of annual rainfall in India occurs during the monsoon season, which lasts from June to September. The monsoon typically begins in early June in coastal areas (Kerala, Karnataka, Goa, and Maharashtra) and by early July in the interior regions. Monsoon rainfall is influenced by relief and topography, with a declining trend as one moves further inland from the coast.
• Retreating Monsoon: By the end of September, the monsoon weakens and moves southward. The weather in northern India becomes dry, while the eastern part of the peninsula may still receive rain.

2. Spatial Distribution of Rainfall:

• The average annual rainfall in India is about 125 cm, but there are significant spatial variations across the country.

Areas of High Rainfall:

• The highest rainfall occurs along the west coast, particularly the Western Ghats, as well as in the sub-Himalayan areas, such as the northeast and the hills of Meghalaya.
• In some parts of the Khasi and Jaintia hills, rainfall exceeds 1,000 cm, while in the Brahmaputra Valley and adjacent hills, rainfall is generally less than 200 cm.

Areas of Medium Rainfall:

• Rainfall ranging between 100-200 cm is experienced in the southern parts of Gujarat, east Tamil Nadu, the northeastern peninsula (covering Odisha, Jharkhand, Bihar), parts of eastern Madhya Pradesh, the northern Ganga plain, and areas along the sub-Himalayas and the Cachar Valley in Manipur.

Areas of Low Rainfall:

• Regions like Western Uttar Pradesh (UP), Delhi, Haryana, Punjab, Jammu and Kashmir, eastern Rajasthan, Gujarat, and the Deccan Plateau receive rainfall between 50-100 cm.

Areas of Inadequate Rainfall:

• Parts of the peninsular region, such as Andhra Pradesh, Karnataka, and Maharashtra, as well as Ladakh and most of western Rajasthan, receive less than 50 cm of rainfall annually.
• Observation: In northern India, rainfall tends to decrease as you move westward, whereas in peninsular India, rainfall decreases from east to west (except in Tamil Nadu).

Characteristics and Reasons of Variability:

• Rainfall decreases from east to west in the plains region: In the summer, there are several low-pressure cells across the plains. As monsoon winds move from east to west, moisture levels decrease due to successive rainfall in each low-pressure zone. By the time the monsoon winds reach the western parts of the plains (such as Delhi and Haryana), most of the moisture has been exhausted, leading to lesser rainfall.
• Haryana and Punjab: These regions do not experience desert-like conditions like Rajasthan because they receive rainfall due to Western Disturbances in winter. However, their summer rainfall is minimal.
• No significant rainfall in Gujarat and Rajasthan: Monsoon winds passing through these areas do not encounter orographic barriers, which is why they receive very little rainfall.
  • Example: The monsoon winds flow almost parallel to the Aravalis, leaving no significant obstruction that could lead to rainfall.
• Semi-arid regions in Peninsular India: Places on the windward side of mountains, like the Western Ghats, receive ample rainfall, while those on the leeward side remain dry or semi-arid due to the rain shadow effect.

• Example: The southwest monsoon winds from the Arabian Sea strike the Western Ghats nearly perpendicularly, causing significant rainfall in the Western Coastal Plain.
• Rain Shadow Area: Regions like Maharashtra, Karnataka, Telangana, Andhra Pradesh, and Tamil Nadu lie in the rain shadow of the Western Ghats and receive scanty rainfall.

• Cherrapunji and Mawsynram: These locations receive abnormally high rainfall due to a funneling effect that channels clouds between mountains, followed by orographic upliftment. The result is extremely dense clouds and heavy rainfall.
• Madden–Julian Oscillation (MJO): The MJO is a significant source of intra-seasonal fluctuations in monsoon systems. About 33–80% of intra-seasonal variability in monsoon rainfall is associated with the MJO.

Changing Pattern of Rainfall in India:

There is a general consensus that India’s monsoon patterns are changing in terms of intensity, duration, frequency, and spatial distribution:

1. Extremes have increased: The frequency of extreme rainfall events has increased threefold over recent years.
2. Floods and droughts increased: There are more frequent floods in the northwest and northeast, while the southern region faces increased rainfall deficits and droughts.
3. Delay in monsoon onset: The onset of the monsoon has been delayed due to a climate regime shift, such as a transition from a weak to a strong El Niño period.
4. Reduced length of the rainy season: Monsoon seasons are ending earlier, reducing the duration of the rainy season.
5. Random breaks: Monsoon seasons are witnessing random break periods, during which there is little or no rainfall.

Factors Affecting Monsoon Patterns:

1. Global warming and climate change: These factors contribute to changes in monsoon intensity and distribution.
2. Frequent El Niño and La Niña: Along with the Indian Ocean Dipole and the Atlantic Niño, these phenomena influence rainfall variability.
3. Break periods: Break periods in the monsoon are linked to rainfall systems moving northward from the equatorial region.
4. Deforestation: Deforestation plays a critical role in disrupting the natural monsoon patterns.

To maintain the balance of the monsoon pattern, India must work towards restoring the balance of nature and collaborating with other nations. This is essential to prevent permanent changes in the monsoon’s behavior.

Significance of Rainfall Variability:

1. Agriculture: Indian farmers heavily depend on the monsoon season. Variability in rainfall can significantly affect agricultural output, leading to droughts or floods.
2. Indirectly affects the economy: Rainfall variability can have an indirect economic effect. If one sector (e.g., agriculture) flourishes or suffers due to rainfall, it has ripple effects on other sectors of the economy.
3. Energy Security: Variations in rainfall alter river flows, which impacts hydropower plants and other water-dependent energy sources.
4. Waterway transport: Inland water transport relies on river water levels, which fluctuate with rainfall. Variability in water flow can affect the movement of goods and services.
5. Fishing and allied activities: Fishing in India is primarily inland, and it depends on river water flows, which are affected by rainfall variability.
6. Drinking water: A significant portion of India’s drinking water comes from underground sources or rainwater. Erratic rainfall patterns can threaten the availability of safe drinking water.

Way Forward

1. Systematic method of water storage: India lacks a comprehensive system to store surplus water. More water is wasted due to inefficient storage methods, and improved strategies are needed to prevent floods and water scarcity.
2. Interlink River Project: The government has been exploring the idea of interlinking rivers. This would involve transferring water from surplus areas to water-deficit regions, improving water management across the country.
3. Mapping climate change: Regions should be mapped to monitor and understand how climate change affects rainfall patterns, so that proper mitigation measures can be taken.
4. Proper weather forecasting: Enhanced weather forecasting, along with flood warning systems, is essential for accurate prediction and preparation in vulnerable regions.

INDIAN OCEAN DIPOLE (IOD)

The Indian Ocean Dipole (IOD) is a coupled atmosphere-ocean phenomenon characterized by temperature differences between the sea surface in the eastern Indian Ocean (Bay of Bengal) and the western Indian Ocean (Arabian Sea). The IOD plays a crucial role in influencing the Indian monsoon, alongside other phenomena like El Niño and La Niña.

Characteristics of IOD:

1. Temperature difference: The IOD is caused by differences in sea-surface temperatures, leading to a pressure difference between the eastern and western parts of the Indian Ocean. This pressure difference drives wind patterns.
2. Development: The IOD typically develops in the equatorial region of the Indian Ocean from April to May, peaking in October.
3. Three Phases of IOD:

• Neutral Phase: During this phase, water flows from the Pacific between Indonesia’s islands, keeping the sea warm northwest of Australia. Air rises above this region and descends over the western Indian Ocean basin, leading to westerly winds along the equator.
• Positive Phase: During the Positive IOD phase, the eastern equatorial Indian Ocean near Sumatra and Indonesia becomes cooler than normal, while the western part of the Indian Ocean near the African coast becomes unusually warm. This phase is generally beneficial for the Indian monsoon, bringing heavy rains to India.
• Negative Phase: The opposite of the Positive IOD. In a Negative IOD phase, the eastern equatorial Indian Ocean (near Sumatra in Indonesia) becomes abnormally warm, while the western tropical Indian Ocean (near the African coast) becomes relatively cooler. This disrupts the monsoon progression over India by preventing moisture-laden winds from reaching the Indian subcontinent.

Impact on the Southwest Monsoon:

• Increased rainfall due to Positive IOD: While no direct correlation is established between the Indian monsoon and IOD, studies suggest that Positive IOD years result in higher-than-normal monsoon rainfall over central India. The Positive IOD has been shown to counteract the effects of El Niño Southern Oscillation (ENSO), leading to increased monsoon rainfall in several ENSO years.
  • Example: In ENSO years like 1983, 1994, and 1997, the Positive IOD helped negate the negative effects of El Niño, resulting in enhanced monsoon rains.
• Droughts due to Negative IOD: In contrast, Negative IOD complements El Niño, exacerbating its effects and leading to severe drought conditions.
  • Example: In 1992, a Negative IOD combined with El Niño led to deficient rainfall in India.
• Cyclones: A Positive IOD results in increased cyclogenesis (formation of cyclones) in the Arabian Sea, while a Negative IOD leads to stronger-than-usual cyclogenesis in the Bay of Bengal. Cyclone formation in the Arabian Sea is suppressed during a Negative IOD phase.

Other Effects:

• Effects of IOD on El Niño: The IOD can amplify the effects of El Niño, making sea-surface temperatures (SST) more powerful in the far eastern regions of the Pacific. It may cause El Niño-like anomalies, particularly in the Indian Ocean region. When coupled with El Niño, the IOD amplifies weather anomalies and can escalate the rate of effects related to El Niño.

2020 IOD Positive Cycle (Effects on Other Countries):

1. Africa:
   • Cyclone Idai (2019): The 2019 East Africa cyclones, including Cyclone Idai, killed thousands due to warmer-than-normal waters offshore. These cyclones were linked to the 2020-21 cyclone season in the southwestern Indian Ocean.
   • Heavy downpours: East Africa experienced devastating heavy rains, with rainfall up to 300% above average between October and mid-November, leading to widespread damage. The Famine Early Warning Systems Network attributed the extreme weather to the positive IOD.

• Flash floods and landslides: Countries such as Djibouti, Ethiopia, Kenya, Uganda, Tanzania, Somalia, and South Sudan have been severely impacted by flash floods and landslides, harming many communities in the region due to IOD-related weather anomalies.

1. Australia:
   • Bushfires: Around 100 bushfires were reported in New South Wales (NSW), with the most severe forming a “mega blaze” north of Sydney.
   • Fire danger: The Australian Bureau of Meteorology warned communities of increased fire danger due to warmer-than-usual days and nights throughout the summer. These conditions are linked to IOD effects.
2. Indonesia:
   • Floods: The 2020 Jakarta floods were attributed to a convective IOD cycle, which disrupted the normal movement of moist air. This caused the moisture to move toward southwest Asia instead of its usual path toward Australia.

MADDEN JULIAN OSCILLATION (MJO)

The Madden Julian Oscillation (MJO) is a large-scale phenomenon characterized by disturbances in clouds, wind, and pressure, which move eastward at a speed of 4-8 meters per second. The MJO circles the globe in approximately 30-60 days, but sometimes, it can take up to 90 days. The MJO mainly affects the tropical region between 30°N and 30°S of the equator. India is within this band, and multiple MJO events can occur within a single monsoon season. Though its effect is mostly seen in the tropics, mid-latitude regions can also feel its influence.

Phases of the Madden Julian Oscillation: The MJO consists of two main phases.

1. Enhanced Rainfall Phase: During this phase, surface winds converge, pushing air upward through the atmosphere. This rising air increases condensation and leads to increased rainfall.
2. Suppressed Rainfall Phase: In this phase, winds at the top of the atmosphere converge, forcing the air to sink. As the air sinks, it dries out, which suppresses rainfall.

Eight Phases/Stages of MJO:

The MJO cycle progresses through eight distinct phases as it travels across the globe. These stages explain how enhanced convection (which leads to increased rainfall) moves from one region to another.

1. Stage 1: Enhanced convection (precipitation) begins over the western Indian Ocean.
2. Stages 2 and 3: Enhanced convection gradually moves eastwards across Africa, the Indian Ocean, and parts of the Indian subcontinent.
3. Stages 4 and 5: Enhanced convection reaches the Maritime Continent (areas like Indonesia and the West Pacific).
4. Stages 6, 7, and 8: Enhanced convection moves further eastward across the western Pacific Ocean and eventually vanishes in the central Pacific.

At the end of the eighth stage, the cycle completes, and the next MJO cycle begins. This cyclical movement plays a significant role in influencing global weather patterns, especially rainfall.

MJO Effect on Indian Monsoon:

1. Intense rainfall in the active phase: During the MJO’s active phase, it brings intense rainfall and frequent cyclonic activity in the tropics, including the onset of the monsoon season in India. It can result in one or two weeks of intense rainfall, as witnessed in June in India.
2. Periodicity of MJO:
   • Short stay: If the MJO cycle lasts around 30 days, it tends to bring good rainfall during the monsoon because it revisits the Indian Ocean frequently over the four-month-long monsoon season.
   • Longer stay: If the MJO cycle exceeds 40 days, it doesn’t provide as much rainfall and can result in a dry monsoon.
   • MJO with El Niño: If the MJO is present over the Pacific Ocean along with an El Niño, it can have detrimental effects on Indian monsoon rainfall.

Effects of MJO on Global Weather:

1. Modulate the time and strength of the monsoon: The MJO can affect both the timing and strength of monsoon seasons globally. Enhanced convection can hasten the onset of the monsoon, while suppressed convection can delay its arrival.
2. Influences tropical cyclones: The MJO influences the frequency and strength of tropical cyclones in nearly all ocean basins. It creates favorable conditions for cyclonic activity, including the Atlantic hurricane season.
3. Changes in Jet Stream: MJO-induced changes in the jet stream can result in significant weather shifts, such as cold air outbreaks or flooding rains in regions like the United States and North America.
4. MJO and ENSO (El Niño Southern Oscillation): The MJO can affect the El Niño and La Niña phenomena. While it doesn’t cause these events, it can accelerate their development or enhance their impacts, especially during weak ENSO periods.
5. SSW (Sudden Stratospheric Warming): Research suggests that the MJO can influence the beginning of SSW events, which are sudden and dramatic warmings of the stratosphere, leading to significant weather anomalies.

EL NIÑO AND LA NIÑA

Under normal circumstances, trade winds blow westward along the equator in the Pacific Ocean, pushing warm surface water from South America toward Asia. This movement causes upwelling, where cold water rises from the depths to replace the displaced warm water. El Niño and La Niña are two opposing climate patterns that disrupt these normal conditions.

El Niño:

• Meaning: El Niño refers to the phenomenon where the surface waters of the central and eastern tropical Pacific Ocean experience warming, leading to above-average sea surface temperatures (SSTs).
• Characteristics:
  • Reversal of winds: Under normal conditions, surface winds (known as easterly winds) blow from east to west along the equator. During El Niño, these winds either weaken significantly or reverse direction, causing westerly winds to blow instead.
  • Not a regular event: El Niño is not a predictable or regularly occurring event. It happens irregularly, typically every two to seven years, but its exact timing is not predictable.

Effects of El Niño:

1. Impact on the Ocean: El Niño affects ocean temperatures, the strength of ocean currents, and the health of coastal fisheries. It also influences weather patterns from Australia to South America and beyond.
2. Increased Rainfall: Warmer surface waters caused by El Niño lead to increased convection and precipitation. This brings heavier rainfall to areas like South America, often leading to coastal flooding and erosion.
3. Positive Impact: In some cases, El Niño has a positive effect. For example, it reduces the likelihood of hurricanes forming in the Atlantic Ocean.
4. In South America: El Niño brings increased rainfall to South America, but it also causes droughts in regions such as Indonesia and Australia. These droughts harm water supplies, threatening both agriculture and reservoirs.
5. Impact on Marine Life: Warmer waters off the coast of Peru and Ecuador during El Niño have devastating effects on marine ecosystems, affecting species that rely on upwelling for nutrients.
6. Fishing Decrease: Fish catches along the South American coast drop significantly during El Niño years because upwelling (which brings cold, nutrient-rich waters to the surface) is reduced or absent.
7. In the Western Pacific: El Niño pushes warm surface waters toward the western Pacific, near Asia and Australia, creating warmer-than-normal sea surface temperatures by about 0.5–4.5°C.
8. Indian Climate: There is a strong inverse relationship between El Niño and the Indian monsoon. El Niño years are often associated with weaker monsoons in India.
9. Drought in India: Since 1871, six of India’s most severe droughts have coincided with El Niño events, including significant droughts in 2002 and 2009.

La Niña:

• Meaning: La Niña is a phenomenon characterized by the cooling of the ocean surface or below-average sea surface temperatures (SSTs) in the central and eastern tropical Pacific Ocean.
• Characteristics:
  • High pressure over Eastern Equatorial Pacific: During La Niña, water temperatures in the Eastern Pacific become cooler than normal, creating strong high pressure over the eastern equatorial Pacific. This leads to intensified trade winds along the equator.

Effects of La Niña:

1. Europe: La Niña typically results in milder winters in Northern Europe (especially in the UK). It can cause colder winters in southern and western Europe, sometimes resulting in snowfall in the Mediterranean region.
2. North America: The continental United States feels the most impact from La Niña. The broader effects include:
   • Stronger winds in the equatorial regions, especially over the Pacific.
   • Favorable conditions for hurricanes in the Caribbean and central Atlantic regions.
   • Increased frequency of tornadoes in various states of the U.S..
3. South America: La Niña often brings drought to countries such as Peru and Ecuador in South America. However, La Niña generally has a positive impact on the fishing industry in western South America, as cooler waters can increase nutrient upwelling, benefiting marine life.
4. Western Pacific: In the Western Pacific, La Niña increases the potential for landfall of tropical cyclones, especially in regions most vulnerable to these effects, such as continental Asia and China.
   • La Niña is associated with heavy floods in Australia.
   • Warmer temperatures are observed along the Western Pacific, the Indian Ocean, and the Somalian coast.
5. India Climate: La Niña usually brings heavier rains and a stronger monsoon to India. This can lead to flood-like conditions in coastal regions.

Monitoring El Niño and La Niña:

1. Scientific Buoys Technology: Scientists, governments, and non-governmental organizations (NGOs) use various technologies, such as buoys, to monitor El Niño.
   • Buoy Meaning: A buoy is an object that floats in water and serves as a locator or warning point for ships. They are often brightly colored (fluorescent).
2. Measuring by Buoys: These buoys measure ocean and air temperatures, currents, winds, and humidity to collect data on El Niño events.
3. Transmission of Data: Buoys transmit collected data to researchers and forecasters worldwide, allowing scientists to predict El Niño more accurately and understand its development and impacts.
4. Oceanic Niño Index (ONI): The ONI is used to measure deviations from normal sea surface temperatures, helping monitor the intensity of El Niño events.
5. Variation in Intensity: El Niño events can vary in intensity:
   • Weak El Niño: May cause a 4–5°F increase in temperature with moderate local effects.
   • Strong El Niño: Can lead to 14–18°F increases, causing significant worldwide climatic changes.

Impact of Climate Change on El Niño and La Niña:

1. More Frequent and Extreme: Climate change may lead to more frequent and extreme El Niño and La Niña events.
2. CO₂ Effect: The impact of CO₂ on ENSO (El Niño Southern Oscillation) sea surface temperature fluctuations may decrease as atmospheric carbon dioxide levels rise.
3. Effect on El Niño: Due to increased evaporation, future El Niño events may lose heat to the environment more quickly.
4. Prevent Temperature Extremes During ENSO: The temperature difference between the eastern and western tropical Pacific may decrease in the future, minimizing extreme temperature events during ENSO cycles.
5. Tropical Instability Waves (TIWs): TIWs may weaken in the future, disrupting La Niña events. Monthly variability in the Pacific and Atlantic Oceans is dominated by these waves.

Differences Between El Niño and La Niña