AIR MASS, FRONTS, CYCLONES AND JET STREAM

Cyclones are large-scale weather systems characterized by low-pressure centers and counterclockwise (in the Northern Hemisphere) or clockwise (in the Southern Hemisphere) circulation. These systems are often associated with strong winds, heavy rain, and other severe weather conditions. Cyclones can form in different regions and under various conditions, including tropical oceans and mid-latitude regions. 

Formation

• Tropical cyclones, also known as hurricanes or typhoons depending on their location, form over warm ocean waters near the equator.
• These storms require warm ocean temperatures (usually above 26.5°C or 80°F) and favourable atmospheric conditions, including low wind shear and high humidity, to develop and intensify.
• As warm, moist air rises from the ocean surface, it condenses and releases latent heat, fueling the storm's growth and intensification.
• Mid-latitude cyclones, also known as extratropical or frontal cyclones, form along weather fronts in the mid-latitudes (between 30° and 60° latitude).
• These cyclones develop as a result of temperature contrasts between air masses, with warm air rising and cold air sinking, leading to the formation of a low-pressure centre and cyclonic circulation.

Structure

• Cyclones are characterized by a central area of low pressure, known as the eye (in tropical cyclones), surrounded by a rotating ring of clouds and thunderstorms called the eyewall.
• In tropical cyclones, the eye is a relatively calm and clear area with light winds and subsiding air, while the eyewall contains the strongest winds and heaviest rainfall.
• In mid-latitude cyclones, the low-pressure centre is often associated with a cold or warm front and a complex system of cloud bands, rain, and thunderstorms.

Impact

• Strong winds capable of causing widespread damage to infrastructure, vegetation, and homes.
• Heavy rainfall leads to flooding, landslides, and mudslides, particularly in coastal and low-lying areas.
• Storm surges, or abnormal rises in sea level, which can inundate coastal regions and cause significant coastal erosion and damage.
• Tornadoes, particularly in the outer bands of tropical cyclones, which can produce localized areas of extreme wind damage.

Tracking and Forecasting

• Meteorologists use a variety of tools and techniques to track and forecast the movement and intensity of cyclones.
• Satellite imagery, weather radar, and aircraft reconnaissance are used to monitor the development and movement of tropical cyclones.
• Numerical weather prediction models are used to simulate the behaviour of cyclones and provide forecasts of their future tracks and intensities.

Cyclones are powerful weather systems characterized by low-pressure centers and rotating winds. These storms can form over tropical oceans or mid-latitude regions and can cause a range of severe weather impacts, including strong winds, heavy rain, and coastal flooding. Understanding the formation, structure, and behaviour of cyclones is essential for mitigating their impacts and providing accurate forecasts and warnings to the public.

Tornadoes are rapidly rotating columns of air that extend from thunderstorms to the ground. They are among the most powerful and destructive weather phenomena, capable of producing extremely high winds, causing widespread damage, and posing serious threats to life and property. 

Formation

• Tornadoes typically form within severe thunderstorms known as supercells, which are characterized by rotating updrafts called mesocyclones.
• The exact mechanism of tornado formation within supercells is not fully understood, but it is believed to involve the interaction of strong vertical wind shear and atmospheric instability.
• As warm, moist air rises rapidly within the thunderstorm updraft, it may begin to rotate horizontally due to wind shear. If this rotating air is tilted vertically by updrafts within the storm, it can develop into a rotating column of air known as a tornado.

Structure

• Tornadoes are characterized by a rotating column of air, or vortex, that extends from the base of a thunderstorm to the ground.
• The visible portion of a tornado is often surrounded by a rotating cloud of debris and dust, known as the condensation funnel or debris cloud.
• Tornadoes vary widely in size and intensity, ranging from relatively weak and short-lived to large and extremely violent storms capable of causing catastrophic damage.

Classification

• Tornadoes are classified based on the damage they cause using the Enhanced Fujita (EF) scale, which ranges from EF0 (weak) to EF5 (violent).
• The EF scale takes into account factors such as wind speed, damage to structures, and the extent of damage along the tornado's path.
• EF0 and EF1 tornadoes typically cause minor damage, while EF2 and EF3 tornadoes can cause significant damage to homes and buildings. EF4 and EF5 tornadoes are the most destructive, capable of completely destroying well-built structures.

Hazards

1. Extremely high winds: Tornadoes can generate winds exceeding 200 miles per hour (320 kilometers per hour), capable of leveling buildings, uprooting trees, and tossing vehicles through the air.
2. Flying debris: The intense winds within tornadoes can turn everyday objects into deadly projectiles, causing injuries and fatalities.

Forecasting and Safety

• Meteorologists use radar, satellite imagery, and weather models to forecast the potential for tornado formation and issue tornado watches and warnings to alert the public.
• Safety measures during tornadoes include seeking shelter in a sturdy building or storm shelter, staying away from windows, and taking cover in a basement or interior room on the lowest level of the building.

Tornadoes are powerful and destructive rotating columns of air that form within severe thunderstorms. They pose significant hazards to life and property and require careful monitoring and preparedness efforts to mitigate their impact. Understanding tornado formation, structure, classification, hazards, and safety measures is essential for minimizing the risk posed by these deadly storms.

Monsoons are large-scale seasonal wind patterns that bring about significant changes in weather conditions, particularly in regions bordering the Indian Ocean and adjacent landmasses. These seasonal winds are characterized by a reversal in direction between winter and summer months and are associated with the alternating wet and dry seasons. 

Definition

• Monsoons are seasonal wind systems that result from differential heating and cooling of land and ocean surfaces.
• The term "monsoon" originates from the Arabic word "mausim," meaning season, and was first used to describe the seasonal reversal of winds in the Indian Ocean region.
• Monsoons are characterized by a change in wind direction between winter (dry) and summer (wet) seasons, along with significant shifts in precipitation patterns.

Types of Monsoons

1. Tropical Monsoons: These occur in regions near the equator, where intense heating of land surfaces during summer months creates low-pressure systems, drawing moist air from nearby oceans. Tropical monsoons are common in South Asia, Southeast Asia, and parts of Africa.
2. Subtropical Monsoons: These occur in subtropical regions, such as the southwestern United States and northern Mexico, where the interaction between land and sea leads to seasonal variations in wind patterns and precipitation.

Phases of Monsoons

• Onset: The onset of the monsoon refers to the establishment of seasonal wind patterns and the arrival of significant rainfall after a dry period. In South Asia, for example, the onset of the summer monsoon is marked by the arrival of the southwest monsoon winds, which bring heavy rainfall to the region.
• Peak: The peak of the monsoon season is characterized by intense rainfall and high humidity, often leading to flooding and agricultural productivity.
• Withdrawal: The withdrawal of the monsoon marks the end of the wet season and the return to drier conditions. In South Asia, the withdrawal of the summer monsoon is marked by the retreat of the southwest monsoon winds and the onset of dry, northeast winds.

Impact of Monsoons

• Monsoons play a crucial role in shaping climate, agriculture, and water resources in affected regions.
• Heavy rainfall during the wet season replenishes water sources, supports agricultural productivity, and sustains ecosystems.
• Conversely, inadequate or excessive rainfall during the monsoon season can lead to droughts, floods, crop failures, and other socioeconomic challenges.

Forecasting and Monitoring

• Meteorological agencies use a variety of tools and techniques to forecast and monitor monsoon patterns, including satellite imagery, weather models, and historical data.
• Early warning systems help communities prepare for and mitigate the impacts of extreme weather events associated with monsoons, such as floods and landslides.

Monsoons are seasonal wind patterns characterized by a reversal in direction between dry and wet seasons. They play a vital role in shaping weather patterns, water resources, and agricultural productivity in affected regions, while also posing challenges such as flooding and drought. Understanding the dynamics and impacts of monsoons is essential for effective climate adaptation and disaster management efforts.

 

6. Fronts

 

Fronts are boundaries between air masses with different characteristics, such as temperature, humidity, and density. These transition zones play a significant role in shaping weather patterns and can lead to the development of various types of precipitation and severe weather. 

Formation

• Fronts form when air masses with contrasting properties come into contact with each other. The interaction between these air masses results in the formation of a transition zone or boundary known as a front.
• There are four main types of fronts: cold fronts, warm fronts, stationary fronts, and occluded fronts.

Types of Fronts

• Cold Fronts: Cold fronts form when a cold air mass advances and displaces a warmer air mass. As the cold air pushes underneath the warm air, it lifts the warm air rapidly, leading to the formation of cumulonimbus clouds and potentially severe thunderstorms. Cold fronts are often associated with abrupt changes in weather conditions, including strong winds, heavy rain, and cooler temperatures.
• Warm Fronts: Warm fronts form when a warm air mass advances and replaces a colder air mass. As the warm air gradually rises over the colder air, it produces stratiform clouds and precipitation, typically in the form of light rain or drizzle. Warm fronts are associated with more gradual changes in weather conditions, including increasing temperatures and humidity.
• Stationary Fronts: Stationary fronts occur when two air masses meet but neither advances significantly. Instead, they remain relatively stationary, with the warmer air rising gradually over the colder air. Stationary fronts can lead to prolonged periods of cloudy weather and light to moderate precipitation.
• Occluded Fronts: Occluded fronts form when a fast-moving cold front overtakes a slow-moving warm front. As the colder air advances and lifts both the warm air ahead of it and the cool air behind it, it creates a complex mixture of clouds and precipitation. Occluded fronts are often associated with widespread cloud cover and precipitation, including rain, snow, or a mix of both.

Weather Associated with Fronts

• Frontal passages are often accompanied by changes in weather conditions, including changes in temperature, humidity, wind direction, and precipitation.
• Depending on the type of front and the atmospheric conditions, fronts can produce a wide range of weather phenomena, including thunderstorms, lightning, heavy rain, snow, and strong winds.
• Fronts can also trigger the development of severe weather events, such as tornadoes, hailstorms, and blizzards, particularly when cold fronts interact with warm, moist air masses.

Forecasting and Monitoring

• Meteorologists use various tools and techniques, including satellite imagery, weather radar, and numerical weather prediction models, to forecast the movement and intensity of fronts.
• Frontal passages are typically accompanied by changes in atmospheric pressure, wind speed, and cloud cover, which can be monitored and analyzed to provide advance warning of impending weather changes.

Fronts are boundaries between air masses with different characteristics and play a critical role in shaping weather patterns and producing various types of precipitation and severe weather. Understanding the dynamics and behaviour of fronts is essential for forecasting and monitoring weather conditions and providing timely warnings to the public.

 

Previous Year Questions 1. Consider the following statements: (upsc 2015) The winds which blow between 30°N and 60°S latitude throughout the year are known as westerlies. The moist air masses that cause winter rains in North-Western region of India are part of westerlies. Which of the statements given above is/are correct? (a) 1 only         (b) 2 only         (c) Both 1 and 2             (d) Neither 1 nor 2 Answer: B 2. Consider the following statements: (upsc 2020) Jet streams occur in the Northern Hemisphere only. Only some cyclones develop an eye. The temperature inside the eye of a cyclone is nearly 10ºC lesser than that of the surroundings. Which of the statements given above is/are correct? (a) 1 only         (b) 2 and 3 only             (c) 2 only               (d) 1 and 3 only  Answer: C 3. With reference to Ocean Mean Temperature (OMT), which of the following statements is/are correct? (upsc 2020) OMT is measured up to a depth of 26ºC isotherm which is 129 meters in the south-western Indian Ocean during January-March. 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 Mains 1. Tropical cyclones are largely confined to South China Sea, Bay of Bengal and Gulf of Mexico. Why? (UPSC 2014) 2. The recent cyclone on east coast of India was called ‘Phailin’. How are the tropical cyclones named across the world? Elaborate. (UPSC 2013)