Structure of Atmosphere

Introduction

The Earth’s atmosphere is a huge envelope of gases that envelops the globe from its surface to more than 10,000 km into space. By controlling temperature, blocking dangerous sun radiation, and supplying vital gases like carbon dioxide and oxygen, it acts as a barrier to safeguard life. The global energy balance, weather patterns, and climatic processes are all significantly influenced by this sensitive system.

The atmosphere is not uniform; rather, it is stratified according to the composition of gases and temperature variations. Each layer contains unique properties, functions, and processes that are essential to preserving the stability and habitability of Earth.

Composition of Atmosphere – Gases and Particles

Up to around 80–100 km, the atmosphere is a uniform combination of gases (homosphere); beyond that, lighter gases like hydrogen and helium predominate (heterosphere).

Gaseous Composition at Sea Level

Aerosols and Particulates

• Volcanic ash, dust, pollen, soot, and salt crystals.• Condensation nuclei are crucial for the creation of clouds.• Affect the equilibrium of solar radiation.

Vertical Structure – Layers of Atmosphere

Temperature fluctuation with height is used to classify the atmosphere into five primary strata.

1. Troposphere – The Weather Factory

Altitude: The elevation ranges from the surface to roughly 8 km at the poles and 16–18 km at the equator.

Temperature Trend: Drops at an average rate of 6.5°C per km with height.

Temperature Range: -60°C (tropopause) to 15°C (surface).

Tropopause Altitude: on average, about 12 km.

Key Features

• Makes up 75–80% of the atmosphere’s bulk.• This is where almost every meteorological phenomenon, including clouds, rain, storms, and cyclones, occurs.• The highest levels of aerosols and water vapour.

  • Jet streams pass close to the upper boundary, or tropopause.

2. Stratosphere – Home of the Ozone Layer

• Altitude: From 12-50 km.
• Temperature Trend: Increases with altitude.
• Temperature Range: -60°C (lower boundary) to 0°C (upper boundary).
• Stratopause: Around 50 km.

Key Features

• Has an ozone layer (20–30 km), which absorbs ultraviolet (UV) light.• The air is very stable and perfect for commercial flights (above turbulence).• There is very little dust and water vapour present.

3. Mesosphere – The Coldest Layer

• Altitude: From 50-80 km.
• Temperature Trend: Decreases with altitude.
• Temperature Range: 0°C to about -90°C (mesopause).
• Mesopause: Coldest point in the atmosphere.

Key Features

• The layer where meteoroids burn up as a result of air molecules rubbing against them.• Extremely low pressure and density.• The emergence of noctilucent clouds, which are uncommon ice clouds that appear after sunset.

4. Thermosphere (Ionosphere) – The High-Temperature Zone

• Altitude: From 80-600 km.
• Temperature Trend: Increases sharply with altitude.
• Temperature Range: Up to 1500°C or higher.

Key Features

• Has ionised particles (plasma), which allows for the reflection of radio waves.• The area where the Earth’s magnetic field interacts with the solar wind to generate auroras.• Satellites in Low Earth Orbit (LEO) and the International Space Station (ISS) are based here.

5. Exosphere – Transition to Outer Space

• Altitude: Above 600 km (up to ~10,000 km).
• Temperature Trend: Highly variable.
• Gas Composition: Primarily hydrogen and helium.

Key Features

• The air is quite rarefied.• A progressive shift to interplanetary space.• Area designated for space probes and high-altitude satellites.

Temperature Profile and Lapse Rates

Atmospheric Pressure Variation

• At sea level: ~1013.25 hPa (hectopascals).
• At 50 km: ~1 hPa.
• Pressure drops exponentially with height due to reduced air molecular density.

Atmospheric Functions and Importance

1. Sustains Life

• Provides carbon dioxide for photosynthesis and oxygen for respiration.

2. Regulates Temperature

• The atmosphere preserves the Earth’s heat balance by releasing greenhouse gases.

3. Protection from Cosmic Threats

• Blocks damaging UV radiation.• Incoming meteoroids are burned.

4. Weather and Climate Regulation

• Regulates climate systems, precipitation, and winds.

5. Enables Communication and Navigation

• Long-distance radio communication is made possible by the ionosphere’s ability to reflect radio signals.

Layers and Their Key Roles

Facts and Figures

• Atmospheric Extent: ~10,000 km.
• Atmospheric Mass in Troposphere: ~75-80%.
• Ozone Layer Altitude: 20-30 km.
• Jet Stream Altitude: 9-16 km.
• Coldest Point: Mesopause (-90°C).
• Aurora Zone: Thermosphere.

Image source: https://www.earthreminder.com/describe-the-composition-of-the-earths-atmosphere/