CLIMATE

COMPOSITION AND STRUCTURE OF ATMOSPHERE

The atmosphere is a vital component of the Earth, essential for sustaining life. It is a mixture of gases, water vapour, and dust particles enveloping the Earth. Air is indispensable for life; humans can survive for days without food and water but only minutes without air. The atmosphere contains life-supporting gases such as oxygen, necessary for animals and humans, and carbon dioxide, essential for plants. Approximately 99% of the atmosphere's total mass is confined within 32 km from the Earth's surface. The air itself is colourless and odourless, perceptible only when it moves as wind. The atmosphere's composition varies with altitude; for example, oxygen becomes almost negligible at about 120 km, and carbon dioxide and water vapour are present only up to 90 km. Carbon dioxide plays a crucial meteorological role by being transparent to incoming solar radiation but opaque to outgoing terrestrial radiation, thus contributing to the greenhouse effect. Its volume has been increasing due to fossil fuel combustion, leading to global warming. Ozone, found between 10 and 50 km altitude, acts as a protective filter absorbing harmful ultraviolet rays from the sun. Water vapour is a variable gas that decreases with altitude and latitude, constituting up to 4% of air volume in warm, wet tropics but less than 1% in cold, dry regions. It absorbs solar radiation and preserves Earth's heat, acting like a blanket to moderate temperature extremes. Dust particles, including sea salts, soil, smoke, ash, pollen, and meteor debris, are concentrated mostly in the lower atmosphere but can be transported higher by convection. These particles serve as nuclei for water vapour condensation, forming clouds. The atmosphere is stratified into five layers based on temperature: troposphere, stratosphere, mesosphere, thermosphere, and exosphere. The troposphere, extending up to 13 km on average (8 km at poles, 18 km at equator), contains dust and water vapour and is the site of all weather and climate changes. Temperature here decreases with height at about 1°C per 165 meters. The tropopause separates the troposphere from the stratosphere and maintains a nearly constant temperature. The stratosphere extends to about 50 km and contains the ozone layer, which shields life from ultraviolet radiation. Above lies the mesosphere (up to 80 km), where temperature decreases again, reaching about -100°C at the mesopause. The ionosphere, between 80 and 400 km, contains charged particles (ions) that reflect radio waves back to Earth. The outermost layer, the exosphere, merges gradually into outer space and contains extremely rarefied gases. While all layers influence Earth, geographers mainly focus on the troposphere and stratosphere, where weather and climate phenomena occur. The main elements of weather and climate include temperature, pressure, winds, humidity, clouds, and precipitation, which are elaborated in subsequent chapters.

• Atmosphere is a mixture of gases, water vapour, and dust particles enveloping Earth.
• 99% of atmospheric mass lies within 32 km of Earth's surface.
• Carbon dioxide is transparent to solar radiation but traps terrestrial radiation, causing the greenhouse effect.
• Ozone layer (10-50 km) absorbs harmful ultraviolet rays from the sun.
• Water vapour varies with altitude and latitude, influencing temperature and weather.
• Atmosphere is divided into five layers: troposphere, stratosphere, mesosphere, thermosphere, and exosphere.
• 📌 Atmosphere: The layer of gases surrounding Earth essential for life.
• 📌 Greenhouse Effect: Warming of Earth's surface due to gases trapping terrestrial radiation.
• 📌 Ozone Layer: A layer in the stratosphere that absorbs ultraviolet radiation.

COMPOSITION OF THE ATMOSPHERE

The atmosphere is composed primarily of gases, water vapour, and dust particles. The major gases include nitrogen (about 78%) and oxygen (about 21%), with other gases like argon, carbon dioxide, and trace gases making up the remainder. The proportion of these gases remains relatively constant up to about 90 km altitude, except for water vapour and carbon dioxide which decrease with height. Carbon dioxide, though a minor component, is meteorologically significant because it is transparent to incoming solar radiation but absorbs outgoing terrestrial radiation, contributing to the greenhouse effect. Its concentration has increased in recent decades due to human activities such as burning fossil fuels, leading to global warming. Ozone, another important gas, is concentrated between 10 and 50 km altitude in the stratosphere. It absorbs harmful ultraviolet radiation from the sun, protecting living organisms on Earth. Water vapour is a variable gas, constituting up to 4% of the atmosphere in warm, humid tropical regions but less than 1% in cold, dry polar and desert areas. It decreases with altitude and latitude and plays a crucial role in weather and climate by absorbing solar radiation and preserving Earth's heat. Water vapour also influences atmospheric stability and instability, affecting cloud formation and precipitation. Dust particles in the atmosphere originate from various sources such as sea salts, soil, smoke, ash, pollen, and meteoric debris. These particles are mostly concentrated in the lower atmosphere but can be transported to higher altitudes by convection. Dust and salt particles act as hygroscopic nuclei around which water vapour condenses to form clouds, playing a vital role in the water cycle and weather phenomena.

• Major gases: Nitrogen (~78%), Oxygen (~21%), Argon, Carbon dioxide, and trace gases.
• Carbon dioxide absorbs terrestrial radiation, causing the greenhouse effect.
• Ozone layer (10-50 km) absorbs ultraviolet radiation.
• Water vapour varies from 4% in tropics to less than 1% in polar and desert regions.
• Dust particles originate from sea salts, soil, smoke, ash, pollen, and meteors.
• Dust particles serve as nuclei for cloud formation.
• 📌 Carbon Dioxide: A greenhouse gas absorbing terrestrial radiation.
• 📌 Ozone: A gas in the stratosphere absorbing ultraviolet rays.
• 📌 Water Vapour: Variable gas influencing weather and climate.