Chapter 3 of 'earth environments past,present,future' -Huddart and Tim Stott

Energy in the Atmosphere and the Earth Heat Budget

Overview

• The Earth’s energy budget consists of all incoming and outgoing energy, achieving an equilibrium where gains equal losses.

• Energy is fundamental to various natural processes such as wind formation, weather patterns, water currents, and photosynthesis.

• Total energy flux to Earth is estimated at 174 petawatts, with 99.978% originating from solar radiation.

Key Concepts

Solar Radiation

• Solar radiation is the primary energy source for Earth, impacting all biological and geological processes.

• Earth absorbs and emits energy in various forms including heat and radiation, which contributes to its energy budget.

Total Energy Flux

• Total energy flux to Earth is about 174 petawatts (1 petawatt = 10^15 watts).

• Breakdown of energy sources:

  • 99.978% from solar radiation (~340 W/m²)

  • 0.013% from geothermal energy (~0.045 W/m²)

  • 0.002% from tidal energy (~0.0059 W/m²)

  • 0.007% from waste heat from fossil fuels (~0.025 W/m²)

Forms of Energy

• Energy exists in forms such as:

  • Kinetic Energy: Energy of movement.

  • Potential Energy: Energy stored in an object based on its position.

  • Thermal Energy (Heat): Total energy of a substance due to molecular motion.

• Temperature vs Heat: Temperature measures average kinetic energy of molecules, while heat measures total kinetic energy.

• Absolute Zero: The lowest temperature possible, 0 K (−273.15 °C).

Heat Transfer Mechanisms

• Heat transfer occurs via:

  • Conduction: Transfer through materials from higher to lower temperature without movement of molecules.

  • Convection: Transfer through fluids where warmer, less dense areas rise and cooler, denser areas sink.

  • Radiation: Energy emitted in the form of electromagnetic waves by all objects above absolute zero.

Electromagnetic Radiation

• Electromagnetic radiation encompasses various wavelengths, measured in micrometers (µm).

• The spectrum ranges from gamma rays and X-rays to ultraviolet radiation, visible light, infrared, microwaves, and radio waves.

Radiation Laws

1. Stefan–Boltzmann Law:

   • Total energy radiated per unit area is proportional to the fourth power of the thermodynamic temperature:

   • Formula: F = σT⁴ (where F = radiant flux, T = temperature in K, σ = Stefan's constant).

2. Wien’s Law:

   • The wavelength of maximum energy emitted from a black body is inversely proportional to the temperature:

   • Formula: λmax = α/T.

Insolation and Albedo

• Insolation refers to solar radiation energy received on an exposed surface.

• Albedo is the reflectivity of surfaces, affecting energy absorption:

  • Different surfaces (like ice, water, forest) have varying albedo values.

Net Radiation

• The concept of net radiation refers to the balance between incoming solar radiation absorbed by Earth and outgoing infrared radiation.

• Net radiation varies across the Earth's surface, with latitudes receiving different solar inputs:

  • Energy surplus between 40°N and 40°S.

  • Energy deficit beyond these latitudes.

Seasonal Variation

• The Earth's axial tilt (23.5°) affects seasonal radiation:

  • Summer/Winter Solstice: North Pole tilted towards Sun results in summer, while the opposite Pole is in winter.

  • Equinoxes: Both hemispheres receive equal sunlight.

Conclusion

• Understanding energy flows in Earth's systems is crucial for climate science and predicting environmental changes.

• Natural processes involve complex interactions of heat transfer and energy distribution influenced by Earth's position relative to the Sun.