Layers of Atmosphere

The Earth's atmosphere which is crucial for climate and weather consists of distinct layers. The troposphere is responsible for weather by influencing winds and monsoons. Above it, the stratosphere protects earth with its ozone layer and stable conditions for aviation. The mesosphere above this shields the Earth and its lifeforms from meteors. Beyond this, the thermosphere with rising temperatures hosts the International Space Station and displays auroras. The exosphere fades into space and holds satellites. This atmospheric structure, influenced by various gas compositions, supports life in a delicate heat budget. This balance of heat budget creates the Earth's climate, highlighting the profound connection between atmospheric dynamics and climate stability. In this era of climate uncertainty and climate change, understanding the atmospheric structure is important for making effective policy decision regarding global warming

Climate and weather play pivotal roles within the Earth system, influencing and being influenced by components such as the atmosphere, hydrosphere, and biosphere, collectively determining the planet's habitability. The surge in Extreme Weather Events (EWE) indicates a growing awareness that the equilibrium of our Earth system is under disruption due to a myriad of natural and human-induced factors, primarily due to climate change. A significant contributor to this climate shift is alterations in atmospheric composition, notably the increase in greenhouse gases such as CO2 and the depletion of ozone. Consequently, a critical understanding of the atmosphere—its structure, composition, and its role in shaping climate and weather patterns—becomes imperative in addressing these complex environmental dynamics.

The Atmosphere is a layer of gases that surrounds a planet, held in place by the planet's gravity. It is an important component for supporting the life on Earth. It furnishes the air essential for breathing, acts as a shield against the Sun's harmful ultraviolet (UV) radiation, retains heat to maintain the planet's warmth, and moderates the temperature extremes. Distinct layers within the atmosphere exhibit temperature variations primarily due to the absorption of solar radiation. At the surface, visible light is absorbed, while near ultraviolet radiation prevails in the middle atmosphere, and far ultraviolet radiation dominates in the upper atmosphere.

The column of atmosphere is divided into five different layers based on its Temperature Troposphere, stratosphere, mesosphere, thermosphere, and exosphere, each is defined by unique features such as temperature and pressure.

1. The Troposphere:
   • Physical Features
     • The troposphere is the lowest layer of the atmosphere having an average height of 13 km, reaching approximately 8 km near the poles and 18 km at the equator due to heat. Its height peaks during summer and is lowest during winter.
     • The temperature declines at the rate of 1° C for every 165m of height.
     • This region is marked by temperature inversion and vigorous convective air currents causing turbulence.
   • Composition:
     • Troposphere composes of dust particles and water vapor, this layer is the site of all climate, weather changes and biological activity.
     • Volume Contains 75-80% of total atmosphere including clouds.
     • 99% of water vapour & Aerosols is found in this region.
   • Regulates weather & climate:
     • The troposphere generates Earth’s winds and shapes weather patterns such as pressure system.
     • The troposphere influences monsoon, jet streams, polar vortex, water cycle and aids in smog formation.
   • The Stratosphere is the layer above the troposphere, divided by the boundary called the "tropopause".
   
   
2. The Stratosphere:
   • Physical Features:
     • The Stratosphere begins above the tropopause extending up to 50 km.
     • Temperatures increase with altitude in the stratosphere, up to the Stratopause
     • Convection and mixing of air in the stratosphere is limited because of which air in the stratosphere is quite stable.
     • There are no clouds or water vapour in the lower stratosphere.
   • Presence of Ozone Layer(Ozonosphere): The ozone layer in stratosphere absorbs harmful ultra-violet radiation, providing a shield against this intense energy and also aids in thermal regulation of stratosphere.
   • Commercial jet aircraft navigate in the lower stratosphere to avoid the turbulence prevalent in the troposphere.
   
   
3. The Mesosphere:
   • Positioned above the stratosphere, the mesosphere extends up to 80 km. Similar to the troposphere, temperatures decline with increasing altitude in this layer, reaching approximately minus 100°C at 80 km.
   • The upper boundary of the mesosphere is termed the mesopause.
   • The mesosphere harbors the coldest temperatures in Earth's atmosphere, dropping to about -90°C (-130°F) near its upper limit.
   • Noctilucent clouds, or night shining clouds, form in the upper atmosphere, specifically in the mesosphere, making them the highest clouds in the sky.
   • The mesosphere serves as the zone where meteors burn up beacuse the presence of sufficient gases in mesosphere causes friction which generates heat, hence protecting earth.
   • Collectively, the stratosphere and mesosphere constitute the middle atmosphere.
   
   
4. The ionosphere
   • The ionosphere is positioned between 80 and 400 km above the mesopause.
   • It comprises electrically charged particles known as ions.
   • It can be subdivided into two layers- Thermosphere and Exosphere.
   • This layer is crucial for radio communication, as it reflects radio waves transmitted from Earth back to the Earth's surface.
   • In this region, temperature experiences an increase with height due to solar radiation.
   
   
5. The Thermosphere
   • Temperature: The temperature in the thermosphere increases altitude, ranging from 600 to 3000 F (600-2000 K). This temperature rise is due to the absorption of intense solar radiation by the limited molecular oxygen in thermosphere.
   • Composition: The atmosphere is extraordinarily rarefied in the thermosphere, with gas molecules spaced hundreds of kilometers apart.
   • The International Space Station (ISS) orbits within the thermosphere.
   • The Thermosphere is marked by moving ions, which when collided with the electrically neutral gases, generates distinctive green lights called Auroras which are observed in Polar regions.
   
   
6. The Exosphere
   • The outermost layer above the thermosphere is termed the exosphere. This is the highest layer, and there is limited knowledge about its characteristics.
   • The contents in this layer are extremely rarefied, gradually blending with outer space with no clear upper boundary.
   • Temperature increases gradually as one moves through the exosphere.
   • Light gases such as helium and hydrogen float into space from the exosphere.
   • The exosphere is home to most of the Earth’s Satellites.
   
   

An alternative approach to characterizing the atmosphere considers whether the gases are uniformly mixed (homosphere) or arranged in layers (heterosphere).

• The homosphere encompasses the troposphere, stratosphere, mesosphere, and the lower thermosphere.
• The heterosphere comprises most of the thermosphere along with the entire exosphere. In this region, gases are stratified based on molecular weight, with oxygen and nitrogen positioned near the bottom and hydrogen and helium at the top.

The atmosphere consists of gases, water vapor, and dust particles, with varying proportions of gases in the upper atmospheric layers.

Permanent Gases in the Atmosphere (Listed in descending order of volume):

1. Nitrogen = 78.08%
2. Oxygen = 20.95%
3. Argon = 0.93%
4. Carbon Dioxide = 0.036%
5. Neon = 0.002%
6. Helium
7. Krypton
8. Xenon
9. Hydrogen

Nitrogen: Nitrogen is taken out of the atmosphere and deposited on Earth's surface, mainly facilitated by nitrogen-fixing bacteria and through precipitation associated with lightning. This deposited nitrogen enriches the soils and various water bodies, providing essential nutrients for plant growth.

Oxygen: It undergoes a continuous exchange between the atmosphere and living organisms through the processes of photosynthesis and respiration. During photosynthesis, oxygen is produced as sunlight converts carbon dioxide and water into glucose. Respiration, conversely, is the process where living organisms consume oxygen and release carbon dioxide.

Water vapor Water vapor is a variable gas in the atmosphere that diminishes as altitude increases. In tropical regions characterized by warmth and humidity, it could make up around 4% of the air volume. Conversely, in arid and frigid zones like deserts and polar regions, its proportion may fall below 1% of the air. It serves crucial roles on Earth:

• It redistributes heat energy through latent heat energy exchange.
• The condensation of water vapor results in precipitation, supplying fresh water to Earth's surface for plants and animals.
• It contributes to warming the Earth's atmosphere through the greenhouse effect.

Carbon Dioxide: The volume of carbon dioxide in the atmosphere has increased by over 35% in the past three centuries. This increase is primarily due to human activities such as burning fossil fuels, deforestation, and other forms of land-use change. Carbon dioxide, besides being a significant greenhouse gas, is naturally cycled between the atmosphere and living organisms through the processes of photosynthesis and respiration.

Earth's atmosphere is a vital layer of gases that sustains life. It has five distinct layers, each with unique features like temperature and pressure. The troposphere houses our weather and climate, while the stratosphere protects us from harmful UV radiation. The mesosphere is the coldest region, and the ionosphere enables radio communication. The thermosphere experiences high temperatures due to solar radiation, while the exosphere, the outermost layer, gradually blends with space. Understanding these layers and their interactions is crucial for studying Earth's climate and space exploration.