UPSC Topic Wise Notes - Upsc Exam Topic wise notes

The atmosphere is a layer of gases that surrounds the Earth and is held in place by gravity. It plays a crucial role in supporting life on Earth by regulating temperature, providing oxygen for respiration, and protecting the planet from harmful radiation.

Composition

The Earth's atmosphere is composed primarily of nitrogen (about 78%) and oxygen (about 21%), with trace amounts of other gases such as argon, carbon dioxide, neon, helium, and methane.
Water vapour is also an essential component of the atmosphere, although its concentration varies depending on factors such as temperature and humidity.

Layers of the Atmosphere

The atmosphere is divided into several layers based on temperature and altitude. The main layers, from lowest to highest, are the troposphere, stratosphere, mesosphere, thermosphere, and exosphere.

Troposphere: The lowest layer of the atmosphere, where weather occurs and most of Earth's clouds and air pollutants are found.
Stratosphere: Above the troposphere, the stratosphere contains the ozone layer, which absorbs and scatters ultraviolet (UV) radiation from the Sun, protecting life on Earth.
Mesosphere: The mesosphere is above the stratosphere and is characterized by decreasing temperatures with altitude. It is where most meteors burn up upon entering Earth's atmosphere.
Thermosphere: The thermosphere is the outermost layer of the atmosphere and is known for its high temperatures due to the absorption of solar radiation. It is also where auroras occur.
Exosphere: The outermost layer of the atmosphere, where molecules gradually transition into space. It merges with the Earth's magnetosphere and extends thousands of kilometres into space.

Functions and Properties

Protection from Solar Radiation: The atmosphere absorbs and scatters harmful UV radiation from the Sun, protecting life on Earth from the damaging effects of excessive exposure.
Greenhouse Effect: Certain gases in the atmosphere, such as carbon dioxide and water vapour, trap heat and contribute to the greenhouse effect, which helps regulate Earth's temperature.
Weather and Climate: The atmosphere plays a crucial role in regulating weather patterns and climate by redistributing heat energy from the Sun around the planet through processes such as convection, conduction, and radiation.
Oxygen for Respiration: Oxygen in the atmosphere is essential for respiration in plants, animals, and other aerobic organisms, enabling them to extract energy from organic molecules.

Human Impacts

Human activities, such as burning fossil fuels, deforestation, and industrial processes, have led to an increase in greenhouse gas concentrations, contributing to global warming and climate change.
Air pollution, including emissions of pollutants such as carbon monoxide, sulfur dioxide, and nitrogen oxides, can degrade air quality and pose health risks to humans and ecosystems.

Understanding the Earth's atmosphere and its properties is essential for studying weather and climate, predicting atmospheric phenomena, and addressing environmental challenges related to air quality and climate change. Continued research and monitoring of the atmosphere are critical for safeguarding the health of the planet and its inhabitants.

3. Composition

The Earth's atmosphere is composed of various gases, particles, and trace elements that together create the air we breathe and the environment in which weather and atmospheric phenomena occur. The composition of the atmosphere can be broken down into several key components.

Major Gases

Nitrogen (N2): Nitrogen is the most abundant gas in the Earth's atmosphere, making up approximately 78% of the total volume. It is an essential component of proteins and nucleic acids and is crucial for the growth and development of living organisms.
Oxygen (O2): Oxygen is the second most abundant gas in the atmosphere, accounting for approximately 21% of the total volume. It is necessary for respiration in aerobic organisms and plays a vital role in combustion and various chemical reactions.
Argon (Ar): Argon is the third most abundant gas in the atmosphere, making up about 0.93% of the total volume. It is a noble gas and is chemically inert, meaning it does not readily react with other substances.
Carbon Dioxide (CO2): Carbon dioxide is present in trace amounts in the atmosphere, making up about 0.04% of the total volume. It plays a crucial role in the greenhouse effect and is a key component of the carbon cycle.

Trace Gases

Water Vapor (H2O): Water vapour is a variable component of the atmosphere, typically ranging from less than 1% to 4% of the total volume. It is the primary greenhouse gas and plays a significant role in the Earth's energy balance, weather patterns, and precipitation.
Neon (Ne), Helium (He), Methane (CH4), Krypton (Kr), Xenon (Xe): These are among the other trace gases present in the atmosphere, each contributing to the overall composition and properties of the air.

Particulate Matter

Particulate matter refers to tiny particles suspended in the atmosphere, including dust, pollen, soot, ash, and aerosols.
These particles can originate from natural sources such as volcanic eruptions, wildfires, and dust storms, as well as human activities such as combustion, industrial processes, and transportation.
Particulate matter plays a role in atmospheric processes, including cloud formation, precipitation, visibility, and air quality. Fine particulate matter (PM2.5) and coarse particulate matter (PM10) are of particular concern due to their impacts on human health and the environment.

Trace Elements

In addition to gases and particulate matter, the atmosphere also contains trace elements such as ozone (O3), nitrogen oxides (NOx), sulfur dioxide (SO2), carbon monoxide (CO), and volatile organic compounds (VOCs).
These compounds can have significant impacts on air quality, human health, and ecosystems, particularly in urban and industrialized areas.

The composition of the Earth's atmosphere is dynamic and can vary depending on factors such as location, altitude, weather conditions, and human activities. Understanding the composition of the atmosphere is essential for studying atmospheric processes, predicting weather and climate patterns, assessing air quality, and addressing environmental challenges such as air pollution and climate change.

4. Gases

The Earth's atmosphere is composed of various gases, each with its own unique properties and concentrations.

Nitrogen (N2): Nitrogen is the most abundant gas in the Earth's atmosphere, making up approximately 78% of the total volume. It is a colourless, odourless, and inert gas, meaning it does not react readily with other substances under normal conditions. Nitrogen is an essential component of proteins and nucleic acids and is crucial for the growth and development of living organisms.
Oxygen (O2): Oxygen is the second most abundant gas in the atmosphere, accounting for approximately 21% of the total volume. It is necessary for respiration in aerobic organisms, enabling the extraction of energy from organic molecules through cellular respiration. Oxygen also plays a vital role in combustion and various chemical reactions, including the oxidation of materials.
Argon (Ar): Argon is the third most abundant gas in the atmosphere, making up about 0.93% of the total volume. It is a noble gas, meaning it is chemically inert and does not readily react with other substances. Argon is used in various industrial applications, such as welding, lighting, and as a shielding gas in metalworking processes.
Carbon Dioxide (CO2): Carbon dioxide is present in trace amounts in the atmosphere, making up about 0.04% of the total volume. It plays a crucial role in the greenhouse effect, trapping heat in the Earth's atmosphere and contributing to global warming and climate change. Carbon dioxide is a byproduct of combustion, respiration, and other natural and human activities.
Water Vapor (H2O): Water vapour is a variable component of the atmosphere, typically ranging from less than 1% to 4% of the total volume. It is the primary greenhouse gas and plays a significant role in the Earth's energy balance, weather patterns, and precipitation. Water vapour is responsible for the formation of clouds, fog, rain, snow, and other forms of precipitation.
Other Trace Gases: The atmosphere also contains trace amounts of other gases, including neon (Ne), helium (He), methane (CH4), krypton (Kr), xenon (Xe), ozone (O3), nitrogen oxides (NOx), sulfur dioxide (SO2), and volatile organic compounds (VOCs), among others. These gases may have important roles in atmospheric chemistry, air quality, and climate processes.

The composition of gases in the atmosphere can vary depending on factors such as location, altitude, weather conditions, and human activities. Understanding the distribution and behaviour of atmospheric gases is essential for studying atmospheric processes, predicting weather and climate patterns, and assessing air quality and environmental impacts.

5. Water Vapour

Water vapour is the gaseous form of water, consisting of water molecules in the gas phase. It is an essential component of the Earth's atmosphere and plays a crucial role in various atmospheric processes, weather patterns, and the Earth's climate system.

Formation and Sources: Water vapour is formed through the process of evaporation, where liquid water changes into water vapour due to heating or increased energy input. It can also be released into the atmosphere through sublimation (the direct transition from solid to gas) and transpiration (the release of water vapour by plants). The primary sources of water vapour include oceans, lakes, rivers, and other surface water bodies, as well as soil moisture and vegetation.
Distribution and Variability: Water vapour is unevenly distributed in the atmosphere, with higher concentrations near the Earth's surface and lower concentrations at higher altitudes. Its concentration in the atmosphere is highly variable and depends on factors such as temperature, humidity, wind patterns, and regional climate conditions. Water vapour concentrations are typically highest in warm and humid environments and lower in cold and dry environments.
Role in the Water Cycle: Water vapour plays a central role in the Earth's water cycle, which involves the continuous movement of water between the atmosphere, land, and oceans through processes such as evaporation, condensation, precipitation, runoff, and groundwater flow. Evaporation and transpiration release water vapour into the atmosphere, where it condenses to form clouds and eventually falls back to the Earth's surface as precipitation (rain, snow, sleet, hail).
Greenhouse Gas and Climate Regulation: Water vapour is the most abundant greenhouse gas in the Earth's atmosphere and plays a critical role in regulating the planet's temperature and climate. It absorbs and emits infrared radiation, trapping heat in the Earth's atmosphere and contributing to the greenhouse effect, which helps maintain the Earth's surface temperature within a habitable range. Changes in water vapour concentrations and distribution can influence cloud formation, precipitation patterns, and regional climate variability, with implications for weather extremes and climate change.
Weather and Cloud Formation: Water vapour is essential for the formation of clouds, which consist of tiny water droplets or ice crystals suspended in the atmosphere. Clouds play a crucial role in weather systems and patterns, affecting factors such as temperature, humidity, precipitation, and atmospheric stability. Water vapour condenses onto microscopic particles known as cloud condensation nuclei (CCN), leading to the formation of cloud droplets and the subsequent development of clouds.

Water vapour is a fundamental component of the Earth's atmosphere, influencing weather, climate, and the distribution of water resources on the planet. Its interactions with other atmospheric constituents and processes are central to understanding Earth's atmospheric dynamics and climate system.

6. Dust Particles

Dust particles, also known as particulate matter (PM), are tiny solid or liquid particles suspended in the air. They can originate from natural sources such as dust storms, volcanic eruptions, wildfires, and sea spray, as well as human activities such as industrial processes, vehicle emissions, construction, and agriculture.

Composition

Dust particles can vary widely in composition, size, shape, and chemical properties depending on their source and atmospheric conditions.
Natural dust sources may contain minerals, soil, pollen, spores, sea salt, and organic matter, while anthropogenic sources may include combustion byproducts, industrial pollutants, and chemical aerosols.

Size Distribution

Dust particles range in size from nanometers (ultrafine particles) to micrometres (fine particles) and larger particles visible to the naked eye.
The size distribution of dust particles influences their behaviour in the atmosphere, including their transport, dispersion, deposition, and interactions with other atmospheric constituents.

Transport and Dispersion

Dust particles can be transported over long distances by wind currents, atmospheric circulation patterns, and weather systems.
Large dust storms and desertification events can generate massive plumes of airborne dust that travel across continents and oceans, impacting air quality, visibility, and weather conditions in distant regions.

Health and Environmental Impacts

Inhalation of dust particles can pose health risks, particularly for vulnerable populations such as children, the elderly, and individuals with respiratory or cardiovascular conditions.
Fine and ultrafine dust particles (PM 2.5 and PM10) can penetrate deep into the lungs and enter the bloodstream, causing or exacerbating respiratory diseases, cardiovascular problems, and other health issues.
Dust deposition on soil, vegetation, water bodies, and built environments can affect ecosystem health, soil fertility, water quality, agricultural productivity, and infrastructure maintenance.

Climate Effects

Dust particles can influence Earth's climate by absorbing or reflecting solar radiation, altering atmospheric temperature profiles, and modifying cloud properties and precipitation patterns.
Dust aerosols can act as cloud condensation nuclei (CCN) or ice nuclei (IN), affecting cloud formation, cloud microphysics, and the radiative properties of clouds.
In regions with high dust emissions, such as deserts and arid areas, dust aerosols can contribute to regional and global climate variability and change.

Dust particles play diverse and complex roles in Earth's atmosphere, affecting air quality, human health, ecosystem dynamics, weather patterns, and climate variability. Understanding the sources, transport mechanisms, and impacts of dust particles is essential for mitigating their adverse effects and managing air quality and environmental health.

7. Structure

The Earth's atmosphere is a complex system composed of multiple layers with varying properties, composition, and dynamics. Understanding the structure of the atmosphere is crucial for comprehending atmospheric processes, weather phenomena, and climate patterns.

7.1. Exosphere

The exosphere is the outermost layer of Earth's atmosphere, extending from the top of the thermosphere to the boundary of space. It is the least dense and most tenuous layer, gradually transitioning into the vacuum of outer space.

Composition: The exosphere contains only a sparse amount of gas molecules and atoms, primarily hydrogen (H), helium (He), oxygen (O), and other trace gases such as carbon dioxide (CO2) and nitrogen (N2). The composition of the exosphere is influenced by processes such as atmospheric escape, solar wind interactions, and outgassing from planetary surfaces.
Density and Pressure: The exosphere is characterized by extremely low densities and pressures, with gas molecules and atoms widely spaced apart. The density of the exosphere decreases exponentially with increasing altitude, and gas molecules are more likely to escape into space rather than collide with each other.
Temperature: Due to the low density of particles in the exosphere, there is no well-defined temperature in this layer. Instead, the temperature can vary significantly depending on factors such as solar activity, time of day, and location. While individual gas particles in the exosphere can have high kinetic energies, the overall temperature of the exosphere is often considered to be very cold, especially in regions away from the Sun.
Boundary with Space: The exosphere gradually transitions into the vacuum of outer space without a clear boundary. Instead, it merges with the interplanetary medium, where the influence of Earth's gravity diminishes, and particles are no longer bound to the planet. The boundary between the exosphere and space is often defined by the Kármán line, located approximately 100 kilometres (62 miles) above sea level. This boundary marks the altitude at which conventional aircraft can no longer maintain lift and must switch to rocket propulsion.
Satellite Orbits: The exosphere is where satellites and spacecraft orbit the Earth, travelling in low Earth orbit (LEO) or geostationary orbit (GEO) to perform various scientific, communication, navigation, and surveillance missions. Satellites in the exosphere experience minimal atmospheric drag and can remain in orbit for extended periods, provided they are periodically boosted to counteract orbital decay.
Auroras and Atmospheric Escape: The exosphere is where interactions between solar wind particles and Earth's magnetic field produce auroras, colourful light displays observed near the poles. Gas particles in the exosphere, particularly hydrogen and helium, can escape into space through processes such as thermal escape, photoionization, and collisional escape. This loss of atmospheric gases contributes to the long-term evolution of Earth's atmosphere and its interactions with the space environment.

The exosphere is a fascinating region of Earth's atmosphere where the boundaries between the planet and outer space blur, and where the effects of solar radiation, planetary motion, and atmospheric dynamics intersect.

7.2. Thermosphere

The thermosphere is a layer of Earth's atmosphere located above the mesosphere and below the exosphere. It is characterized by high temperatures and is known for its ability to absorb large amounts of solar radiation.

Altitude and Extent: The thermosphere extends from the mesopause, which marks the boundary between the mesosphere and the thermosphere, to an altitude of about 600 kilometres (373 miles) above the Earth's surface. It is the fourth layer of the atmosphere, situated above the stratosphere and mesosphere and below the exosphere.
Temperature Profile: Despite its name, the thermosphere is not uniformly hot. While temperatures can soar to thousands of degrees Celsius in the upper thermosphere, the density of gas molecules is so low that it would not feel hot to the touch. Temperature increases with altitude in the thermosphere due to the absorption of solar radiation by gases such as oxygen and nitrogen. However, the low density of gas molecules means that there are few collisions between particles, resulting in a lack of thermal conduction.
Solar Radiation Absorption: The thermosphere is known for its ability to absorb large amounts of solar radiation, particularly in the form of ultraviolet (UV) and X-ray radiation. The absorbed solar energy causes the thermosphere to heat up, leading to the high temperatures observed at higher altitudes.
Auroras: The thermosphere is where auroras, such as the aurora borealis (Northern Lights) and aurora australis (Southern Lights), occur. The interaction of charged particles from the Sun with gases in the upper atmosphere causes these colourful light displays. Solar wind particles and magnetospheric electrons collide with gas molecules in the thermosphere, exciting them and causing them to emit light at various wavelengths.
Satellite Orbits: The thermosphere is where many satellites and spacecraft orbit the Earth. Satellites in low Earth orbit (LEO) typically travel through the lower thermosphere, while those in geostationary orbit (GEO) are located above the thermosphere in the exosphere. The low density of gas molecules in the thermosphere means that satellites experience minimal atmospheric drag, allowing them to maintain stable orbits for extended periods.
Ionosphere: The thermosphere contains a region known as the ionosphere, where gas molecules are ionized by solar radiation. This ionization leads to the formation of charged particles, or ions, which can reflect radio waves and affect radio communications and navigation systems. The ionosphere plays a crucial role in long-distance radio communication, high-frequency (HF) radio propagation, and global positioning system (GPS) signals.

The thermosphere is a dynamic and complex region of Earth's atmosphere, characterized by high temperatures, solar radiation absorption, and the occurrence of auroras. Its unique properties make it an important area for scientific research and space exploration.

7.3. Mesosphere

The mesosphere is the third layer of Earth's atmosphere, situated above the stratosphere and below the thermosphere. It is characterised by decreasing temperatures with increasing altitude and is home to various atmospheric phenomena.

Altitude and Extent: The mesosphere extends from the stratopause, which marks the boundary between the stratosphere and the mesosphere, to an altitude of about 85 kilometres (53 miles) above the Earth's surface. It is situated above the troposphere and stratosphere and below the thermosphere in the atmospheric layering.
Temperature Profile: Temperature decreases with altitude in the mesosphere, reaching extremely cold temperatures as low as -90°C (-130°F) at the mesopause, the boundary between the mesosphere and the thermosphere. The mesosphere experiences some of the coldest temperatures in the Earth's atmosphere due to its high altitude and low pressure.
Atmospheric Dynamics: The mesosphere is characterized by turbulent mixing and vertical transport of gases, which play a role in redistributing heat and atmospheric constituents. Gravity waves, atmospheric tides, and planetary-scale waves generated by weather systems in the troposphere and stratosphere can propagate into the mesosphere, influencing its dynamics and circulation patterns.
Noctilucent Clouds: Noctilucent clouds, also known as polar mesospheric clouds, form in the mesosphere at high latitudes during the summer months. These wispy, iridescent clouds are composed of ice crystals and are visible at twilight when illuminated by sunlight from below the horizon.
Meteor Showers: The mesosphere is where most meteors burn up upon entering the Earth's atmosphere, producing visible streaks of light known as shooting stars or meteors. Meteoroids, fragments of asteroids or comets, collide with gas molecules in the mesosphere, generating heat and ionizing the air to produce luminous trails.
Ionization: The mesosphere contains a layer of ionized gases known as the mesopause, where ultraviolet (UV) radiation from the Sun and cosmic rays ionize atmospheric molecules. The ionization of gases in the mesosphere contributes to the formation of the ionosphere, a region of the upper atmosphere important for radio communication and navigation.

The mesosphere is a dynamic and important region of Earth's atmosphere, playing a role in atmospheric circulation, climate dynamics, and the interaction of Earth with extraterrestrial objects such as meteors and cosmic rays. Its unique properties and phenomena make it an area of scientific interest and research.

7.4. Stratosphere

The stratosphere is the second layer of Earth's atmosphere, situated above the troposphere and below the mesosphere. It is characterized by increasing temperatures with altitude and the presence of the ozone layer.

Altitude and Extent: The stratosphere extends from the tropopause, which marks the boundary between the troposphere and the stratosphere, to an altitude of about 50 kilometres (31 miles) above the Earth's surface. It is situated above the troposphere and below the mesosphere in the atmospheric layering.
Temperature Profile: Unlike the troposphere, where temperature decreases with altitude, the stratosphere exhibits a temperature inversion, with temperatures generally increasing with altitude. This temperature inversion is due to the presence of the ozone layer, which absorbs ultraviolet (UV) radiation from the Sun, leading to the heating of the stratospheric gases.
Ozone Layer: The stratosphere contains a layer of ozone (O3) molecules known as the ozone layer, which is primarily located in the lower portion of the stratosphere between about 10 and 50 kilometres (6 to 31 miles) altitude. Ozone molecules in the ozone layer absorb UV radiation from the Sun, particularly UV-B and UV-C rays, preventing them from reaching the Earth's surface and protecting living organisms from harmful radiation. The concentration of ozone in the ozone layer is not uniform and can vary with altitude, latitude, and season. Ozone concentrations are highest in the tropics and lower at higher latitudes.
Stratospheric Circulation: The stratosphere experiences relatively stable atmospheric conditions with weak vertical mixing compared to the troposphere. Large-scale circulation patterns, such as the Brewer-Dobson circulation, play a role in transporting gases, including ozone, between the tropics and polar regions in the stratosphere.
Aviation and Weather: The stratosphere is an important region for aviation, particularly for commercial jet aircraft flying at high altitudes. Jet streams, which are fast-flowing air currents, can be found in the upper stratosphere and are utilized by aircraft to enhance fuel efficiency and reduce flight time. Weather phenomena such as thunderstorms, clouds, and turbulence are rare in the stratosphere due to its stable and dry conditions.
Climate and Climate Change: Changes in the stratospheric ozone layer, such as ozone depletion caused by human-made chlorofluorocarbons (CFCs), have significant implications for Earth's climate and atmospheric chemistry. Ozone depletion leads to increased UV radiation at the Earth's surface, which can have harmful effects on human health, ecosystems, and materials. Understanding the dynamics of the stratosphere and the ozone layer is essential for monitoring and mitigating the impacts of human activities on Earth's atmosphere and climate.

The stratosphere is a critical component of Earth's atmosphere, protecting from harmful UV radiation and influencing global climate patterns. Its unique properties and processes make it an area of active scientific research and study.

7.5. Troposphere

The troposphere is the lowest layer of Earth's atmosphere, extending from the Earth's surface up to an average altitude of about 8 to 15 kilometres (5 to 9 miles) above sea level. It is characterised by decreasing temperatures with increasing altitude and is where most weather phenomena occur.

Altitude and Extent: The troposphere extends from the Earth's surface up to the tropopause, which marks the boundary between the troposphere and the stratosphere. It is the lowest layer of the atmosphere and is where the majority of Earth's weather, climate, and atmospheric processes take place.
Temperature Profile: Temperature generally decreases with altitude in the troposphere, with an average lapse rate of about 6.5°C per kilometre (3.5°F per 1,000 feet). This temperature gradient is primarily due to the absorption of solar radiation by the Earth's surface, leading to the warming of the lower troposphere, and the adiabatic cooling of air as it rises and expands.
Weather and Atmospheric Processes: The troposphere is where most weather phenomena occur, including clouds, precipitation, storms, and wind patterns. Air circulation in the troposphere is driven by uneven heating of the Earth's surface by the Sun, leading to the formation of convective currents, atmospheric convection, and vertical mixing of air masses.
Moisture and Cloud Formation: The troposphere contains most of the Earth's water vapour and is the primary region where clouds form and precipitation occurs. Water vapour in the troposphere plays a crucial role in regulating Earth's climate and weather patterns through processes such as evaporation, condensation, and latent heat release.
Airplane Flight and Human Activities: The troposphere is where commercial aircraft operate, flying at altitudes typically ranging from the surface up to about 10 kilometres (6 miles) above sea level. Human activities such as pollution emissions, industrial activities, agriculture, and transportation release pollutants and greenhouse gases into the troposphere, influencing air quality, climate, and environmental health.
Tropospheric Circulation: Large-scale circulation patterns, such as the Hadley cells, Ferrel cells, and polar cells, drive atmospheric circulation in the troposphere, transporting heat, moisture, and energy between the equator and the poles. These circulation patterns play a fundamental role in shaping global climate patterns, regional weather systems, and the distribution of heat and moisture across the Earth's surface.

The troposphere is a dynamic and vital component of Earth's atmosphere, serving as the primary region where weather and atmospheric processes occur. Its structure, circulation, and interactions with the Earth's surface and other atmospheric layers play a crucial role in regulating Earth's climate, weather patterns, and environmental conditions.

8. Altitude vs. Temperature

The relationship between altitude and temperature in the Earth's atmosphere is complex and influenced by various factors, including solar radiation, atmospheric composition, and atmospheric dynamics. Generally, temperature tends to decrease with increasing altitude, a phenomenon known as the lapse rate. However, this relationship is not uniform and can vary depending on the location, time of day, and atmospheric conditions.

Troposphere: In the troposphere, the temperature typically decreases with increasing altitude at a rate of about 6.5°C per kilometre (3.5°F per 1,000 feet), known as the environmental lapse rate. This decrease in temperature is primarily due to the adiabatic expansion of air as it rises and expands, leading to a decrease in air pressure and temperature. Near the Earth's surface, the troposphere is warmed by the absorption of solar radiation by the Earth's surface, while higher altitudes receive less direct solar heating, resulting in cooler temperatures.
Stratosphere: In the stratosphere, temperature generally increases with altitude due to the presence of the ozone layer, which absorbs ultraviolet (UV) radiation from the Sun and heats the surrounding air. This temperature increase, known as a temperature inversion, is in contrast to the troposphere and occurs from an altitude of about 15 kilometres (9 miles) up to the stratopause at approximately 50 kilometres (31 miles).
Mesosphere: In the mesosphere, temperature decreases with increasing altitude, similar to the troposphere, but at a much lower rate. Temperatures in the mesosphere can reach extremely cold values, dropping as low as -90°C (-130°F) at the mesopause. The decrease in temperature in the mesosphere is primarily due to radiative cooling and the low density of gases at these altitudes.
Thermosphere: In the thermosphere, temperature increases with altitude due to the absorption of solar radiation by gases such as oxygen and nitrogen. However, despite the temperature increase, the density of gas molecules in the thermosphere is extremely low, and the region does not feel hot. The temperature in the thermosphere can vary widely depending on solar activity, with temperatures reaching thousands of degrees Celsius at higher altitudes during periods of high solar activity.

The relationship between altitude and temperature in the atmosphere is influenced by a combination of factors, including solar radiation, atmospheric composition, adiabatic processes, and heat transfer mechanisms. Understanding these relationships is essential for studying atmospheric dynamics, climate patterns, and weather phenomena.

Previous Year Questions

1. With reference to the Earth's atmosphere, which one of the following statements is correct? (250 Words)

(a) The total amount of insolation received at the equator is roughly about 10 times of that received at the poles.

(b) Infrared rays constitute roughly two-thirds of insolation.

(d) Infrared waves are a part of the visible spectrum of electromagnetic waves of solar radiation.

Answer: C

2. Consider the following statements: (UPSC 2018)

The Earth’s magnetic field has reversed every few hundred thousand years.
When the Earth was created more than 4000 million years ago, there was 54% oxygen and no carbon dioxide.
When living organisms orginated, they modified the early atmosphere of the Earth.

Which of the statements given above is/are correct?

(a) 1 only (b) 2 and 3 only (c) 1 and 3 only (d) 1, 2 and 3

Answer: C

Mains

1. Troposphere is a very significant atmosphere layer that determines weather processes. How? (upsc 2022)

ATMOSPHERE

ATMOSPHERE

ATMOSPHERE

ATMOSPHERE

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