Study Notes on Earth's Atmosphere and Global Wind Patterns

Earth's Atmosphere

Gases of Earth's Atmosphere

  • Nitrogen (N₂) - 78%

    • Mostly exists in the form of molecular nitrogen (N₂).

    • Unusable directly by plants without being fixed.

  • Oxygen (O₂) - 21%

    • Produced by photosynthesis in plants.

    • Essential for respiration in both animals and plants.

  • Argon - 0.93%

    • An inert, noble gas with no significant chemical activity.

  • Water Vapor - 0-4%

    • Varies by region and atmospheric conditions.

    • Acts as a temporary greenhouse gas (GHG), although it is less concerning compared to CO₂ because it cycles quickly through the atmosphere.

  • Carbon Dioxide (CO₂) - 0.04%

    • The most significant greenhouse gas in terms of 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 is comprised of major gases, each with different relative abundances.

    • It is structured into layers based on temperature gradients, which include:

    • Troposphere

    • Stratosphere

    • Mesosphere

    • Thermosphere

    • Exosphere

Layers of Earth's Atmosphere

  1. Troposphere

    • Extends from 0 to approximately 16 km.

    • Most dense layer due to the weight of the gases above it.

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

    • Temperature decreases with altitude.

    • Ozone (O₃) in this layer is harmful, leading to respiratory issues and smog formation.

  2. Stratosphere

    • Ranges from approximately 16 km to 60 km.

    • Less dense due to lower pressure.

    • Contains the ozone layer, which absorbs harmful UV-B and UV-C rays that can mutate DNA, potentially leading to cancer.

    • Temperature increases with altitude due to ozone layer absorbing UV rays.

  3. Mesosphere

    • Extends from approximately 60 km to 85 km.

    • Even less dense and temperature decreases since fewer molecules are there to absorb solar radiation.

  4. Thermosphere

    • From approximately 85 km to 600 km above Earth.

    • The hottest layer, with temperatures reaching up to 3,100°F (approximately 1,704°C) due to absorption of highly energetic solar radiation.

    • Contains charged gas molecules; this layer produces auroras (e.g., aurora borealis).

  5. Exosphere

    • Outermost layer where the atmosphere merges with space.

Temperature Gradient in the Atmosphere

  • Thermosphere: Temperature increases due to high-energy solar absorption.

  • Mesosphere: Temperature decreases with altitude due to lesser density and fewer absorbing molecules.

  • Stratosphere: Temperature increases as altitude increases due to ozone absorption.

  • Troposphere: Temperature decreases as altitude increases due to loss of heat from Earth’s surface.

Global Wind Patterns

Atmospheric Circulation

  • Influences include:

    • Energy from sunlight.

    • Density properties of air.

    • The rotation of Earth (Coriolis Effect).

Air Properties

  • Warm air rises because it is less dense.

  • Warm air can hold more moisture than cold air.

  • Rising air experiences less pressure, which causes it to expand in volume.

    • This expansion leads to adiabatic cooling (cooling caused by expansion).

  • Sinking air experiences more pressure; contraction causes it to heat up (adiabatic heating).

  • Cool air cannot hold as much water vapor as warm air, causing it to condense and rain.

Coriolis Effect

  • Refers to the apparent deflection of objects traveling through the atmosphere due to Earth’s rotation.

    • Air at 30° latitude moves back to lower pressure at the equator.

    • Winds between 0-30° move from west to east.

    • Winds between 30°-60° move from east to west because Earth spins faster at 30° (~870 mph) compared to 60° (~500 mph).

Global Wind Patterns

  1. Intertropical Convergence Zone (ITCZ)

    • Located at the equator; intense solar heating leads moist tropical air to rise.

    • Air moving out from 30° latitude toward 0° and 60° due to high pressure at 30° and low pressure at 0° and 60°.

    • The air that rises at the equator is associated with low pressure, while descending air at 30° latitude is associated with high pressure.

    • Winds blowing between 0°-30° are referred to as easterlies (Eastern trade winds).

  2. Hadley Cells

    • Located between 0° to 30° with high moisture.

    • High pressure at 30° results in hot, dry deserts.

    • Moisture is released as rain at the ITCZ.

  3. Ferrel Cells

    • Occur between 30° to 60°.

    • This area has more variable weather patterns driven by westerly winds.

  4. Polar Cells

    • Extends from 60° to the poles.

    • Cold, polar air dominates resulting in dry conditions.

Key Implications of Wind Patterns

  • Global wind patterns drive ocean currents which rotate clockwise in the Northern Hemisphere and counterclockwise in the Southern Hemisphere.

  • Winds contribute to the climate and weather patterns experienced throughout the continental United States.

Summary of Atmospheric Layers and Characteristics

  • Troposphere: Most dense, temperature decreases, common weather phenomena occur.

  • Stratosphere: Contains ozone layers, temperature increases.

  • Mesosphere: Least dense, temperature decreases.

  • Thermosphere: Hottest layer, absorbs high-energy radiation, molecular excitation produces auroras.

  • Exosphere: Outermost boundary where atmosphere transitions into space.