Lecture 6 Part 1 Notes on Earth's Energy Balance and Heat Transfer

Earth’s Energy Balance

  • Definition: The balance between solar radiation inputs (insolation) and outputs of the earth (radiation to space).
  • Insolation: Solar radiation intercepted by Earth (incoming solar radiation).
  • Inputs: Shortwave radiation (UV, visible light, near-infrared wavelengths).
  • Outputs: Longwave radiation (thermal infrared wavelengths).
  • Transmission: Energy passes through the atmosphere without interruption.

Earth’s Energy Budget

  • Steady-State Equilibrium: Overall energy system remains balanced but varies by location on Earth.

Energy and Heat

  • Heat Definition: Flow of kinetic energy between different bodies resulting from temperature differences.
  • Kinetic Energy: Energy of motion linked to molecular vibration measured as temperature.

Sensible Heat vs Latent Heat

  • Sensible Heat: Heat we can sense, associated with temperature.
  • Latent Heat: Energy involved in phase changes of substances (e.g., liquid to gas).

Methods of Heat Transfer

  1. Radiation:
  • Transfer of heat via electromagnetic waves that can travel through vacuums.
  • Wien’s Law: Hotter objects emit shorter wavelengths.
  1. Conduction:
  • Molecule-to-molecule heat transfer through materials.
  • Efficiency of transfer varies by material conductivity.
  1. Convection:
  • Physical mixing or circulation of heat, often involving vertical motion in fluids.
  • Warmer, less dense substances rise; cooler, denser ones sink.

Examples of Heat Transfer in Environment

  • Radiation and Conduction:
  • Differences in temperature between land and water, lighter and darker surfaces, soil layers.
  • Convection:
  • Atmospheric and oceanic circulation, air mass movements, and internal Earth motions.
  • Advection:
  • Horizontal wind movements among land and sea.

Insolation at the Earth's Surface

  • Variation in solar radiation received across different regions of the Earth.
  • Average annual solar radiation represented in watts per square meter.

Energy Budget by Latitude

  • Equatorial regions: Energy surplus due to direct sunlight.
  • Polar regions: Energy deficit; energy is transported poleward from surplus areas.

Daily Solar Radiation Patterns

  • Key Moments: Midnight (coolest), Local Noon (warmest), Lag after noon.
  • Temperature variations throughout the day due to insolation absorption and release.

Scattering

  • Definition: Insolation reflected back into space.
  • Influencers: Atmospheric gases, dust, water vapor, and pollutants.
  • Diffuse Radiation: Scattered energy reaches Earth without shadows.

Scattering Principles

  • Rayleigh’s Scattering: Shorter wavelengths scatter more (blue sky effect), longer wavelengths scatter less (red sunsets).
  • Mie Scattering: Larger particles scatter all color wavelengths evenly resulting in white light.

Refraction

  • Definition: Bending of insolation as it moves through different mediums like air and water.
  • Effect: Causes phenomena like rainbows and extended daylight at sunrise/sunset.

Reflection and Albedo

  • Reflection: Portion of energy bounces back into space.
  • Albedo: Reflective quality of surfaces, with higher percentages for lighter surfaces.

Absorption

  • Energy Assimilation: Radiation absorbed by materials converts to heat or chemical energy.
  • Breakdown of incoming solar radiation absorption:
  • 31% reflected,
  • 45% absorbed by surfaces,
  • 24% absorbed by atmosphere.

Atmospheric Gases and Aerosols

  • Selective Absorption: Oxygen and ozone absorb UV radiation; CO2 and water vapor absorb longwave radiation.
  • Aerosols Impact: Volcanic eruptions can cool the climate by injecting particles into the atmosphere.

Global Dimming

  • Decline in insolation from pollution: Haze can cool Earth, leading to less evaporation and moisture.

Greenhouse Effect

  • Delays longwave radiation escaping to space, essential for life by maintaining warmth on Earth.
  • Gases involved: CO2, methane, nitrous oxide, and water vapor.

Effects of Clouds

  • Dual function: Can cool (reflecting sunlight) and warm (trapping heat).
  • Impact based on cloud cover, type, altitude, and thickness.

Urban Heat Island (UHI) Effect

  • Urban areas retaining heat due to buildings and surfaces like pavements.
  • Temperature can be significantly higher within urban areas compared to rural areas.
  • Solutions: Green roofs mitigate heat absorption.

Solar Power

  • Pros: Renewable, low maintenance, no operational emissions.
  • Cons: Environmental impact from production and disposal, energy storage challenges.

How Solar Panels Work

  • A functioning mechanism to convert solar energy into usable power.