Earth's Atmosphere and Climate

Earth's Atmosphere

Gases of Earth's Atmosphere

  • Nitrogen: 78%

    • Mostly in the form of N₂

    • Unusable to plants without fixation processes.

  • Oxygen: 21%

    • Produced by photosynthesis in plants.

    • Necessary for respiration in animals and plants.

  • Argon: 0.93%

    • An inert, noble gas with minimal reactivity.

  • Water Vapor: 0-4%

    • Varies by region and atmospheric conditions.

    • Acts as a temporary greenhouse gas (GHG), though less concerning than CO₂.

    • Cycles quickly through the atmosphere.

  • Carbon Dioxide (CO₂): 0.04%

    • The most important greenhouse gas contributing to global warming.

    • Removed from the atmosphere primarily through photosynthesis.

Structure of the Earth's Atmosphere

Learning Objective

  • Describe the structure and composition of the Earth's atmosphere.

Essential Knowledge

  • The atmosphere comprises major gases each contributing to its relative abundance.

  • The atmosphere's layers are defined by temperature gradients and include:

    • Troposphere

    • Stratosphere

    • Mesosphere

    • Thermosphere

    • Exosphere

Layers of Earth's Atmosphere

  1. Exosphere

    • Outermost layer where the atmosphere merges with outer space.

  2. Thermosphere

    • Characterized as the hottest layer

    • Range: 85 km to 600 km above Earth

    • Temperature increases due to absorption of highly energetic solar radiation, reaching temperatures of up to 3,100°F.

    • Absorbs harmful X-rays and UV rays, which can produce phenomena such as the northern lights (aurora borealis).

  3. Mesosphere

    • Middle layer (from 50 to 85 km) where temperature decreases as density decreases, leaving fewer molecules to absorb sunlight.

  4. Stratosphere

    • Layer between 16 km and 50 km.

    • Less dense due to lower pressure from layers above it.

    • Contains the ozone layer (peak ozone layer for UV absorption that can damage DNA).

    • Temperature increases due to the ozone layer absorbing UV-B and UV-C rays.

  5. Troposphere

    • Extends from 0 km to 16 km, the densest layer due to pressure from the overlying layers.

    • Contains most of the atmosphere's gas molecules and water vapor.

    • Temperature decreases with altitude as a result of being further from the Earth's surface heat.

    • Ozone in this layer (O₃) is a respiratory irritant and damages plant stomata, contributing to smog.

Temperature Gradients of the Atmosphere

  • Troposphere: Temperature decreases as one moves farther from the Earth's surface.

  • Stratosphere: Temperature increases with altitude due to ozone layer heating.

  • Mesosphere: Temperature decreases due to fewer molecules as elevation increases.

  • Thermosphere: Temperature spikes upwards due to energy absorption.

Global Wind Patterns

Atmospheric Circulation

Learning Objective

  • Explain how environmental factors can result in atmospheric circulation.

Essential Knowledge

  • Global wind patterns are influenced by:

    • Intense solar radiation at the equator, leading to density differences.

    • The Coriolis Effect, which demonstrates the deflection of air due to Earth's rotation.

Key Concepts on Air Properties

  1. Warm air rises due to lower density.

  2. Warm air can hold more moisture than cold air.

  3. Expanding air experiences less pressure, which leads to adiabatic cooling.

  4. Sinking air experiences increased pressure leading to adiabatic warming.

  5. Cool air has lower capacity for moisture, resulting in condensation (leading to precipitation).

Adiabatic Processes

  • Adiabatic Cooling: The process of rising air cooling due to expansion as it moves to lesser pressure.

  • Adiabatic Heating: The process where descending air warms up as it is compressed under higher pressure.

The Coriolis Effect

  • The Coriolis Effect describes the appearance of deflection of moving objects in the atmosphere due to Earth's rotation.

    • At 30°N, air moves back toward low pressure areas like the equator.

    • Winds at 0° to 30° N blow from west to east (eastern trade winds).

    • Between 30° to 60° N, winds blow from east to west (westerlies).

    • Between 30° to 60° S also feature westerlies.

Hadley Cells

  1. At the Intertropical Convergence Zone (ITCZ), moist tropical air is heated, causing it to rise.

  2. This rising air creates low pressure at the equator.

  3. As it rises, it cools and water condenses into rain, falling back to Earth.

  4. The cool, dry air descends approximately at 30° latitude, creating high pressure areas.

  5. The descending air flows back towards the equator as warm, dry air.

Wind Diagramming & Patterns

  • As a result, at 30° latitude, areas experience high pressure (deserts), and moisture travels from the ITCZ towards the poles.

  • The actions of these differing pressures and temperatures create distinct climates in various regions.

Summary of Global Wind Patterns

  • Winds are directed by the rotation of the Earth and variations in temperature, leading to complex global circulation patterns.

  • The interaction between air cells (Hadley, Ferrel, and Polar cells) creates specific weather patterns and climatic conditions around the globe.