Solar Radiation and the Seasons Notes

Chapter 2: Solar Radiation and the Seasons

  • Key geography for seasons

    • Arctic Circle: 66.5° N
    • Tropic of Cancer: 23.5° N
    • Equator
    • Tropic of Capricorn: 23.5° S
    • Vernal (Spring) Equinox: March 21–22 — Incoming solar energy is equal in both hemispheres.
    • Summer Solstice: June 21–22 — Incoming solar energy greatest in the Northern Hemisphere.
    • Autumnal (Fall) Equinox: September 22–23 — Incoming solar energy equal in both hemispheres.
    • Winter Solstice: December 21–22 — Incoming solar energy greatest in the Southern Hemisphere.
    • Note: The seasonal cycle is driven by Earth’s tilt and orbital geometry, not solely by distance to the Sun.

  • Energy: what it is and basic forms

    • Energy is defined as the ability to do work.
    • Kinetic energy: the energy of motion.
    • Potential energy: energy that can be used; includes gravitational and chemical potentials.
    • Forms of energy include motion (kinetic), light and other radiation, heat, electrical power, etc.
    • Examples of chemical potential energy (five types): Battery, Gasoline, Firewood, Food, Explosives.
    • Reservoir behind a hydroelectric dam is a classic potential-energy example (gravitational potential energy).
    • Energy is conserved (First Law of Thermodynamics): the total amount of energy remains constant, though it can move between objects/systems.

  • Energy transfer mechanisms (ways energy moves even though total energy is conserved)

    • 1) Conduction: heat transfer by physical contact, from regions of higher temperature to lower temperature.
    • 2) Convection: heat transfer by the movement of fluid (air or water); vertical transport of heat.
    • 3) Radiation: transfer of energy by electromagnetic radiation; does not require a medium.

  • Conduction in the atmosphere

    • Occurs at the atmosphere–surface interface.
    • Partly responsible for daytime heating and nighttime cooling (the diurnal cycle).

  • Convection in the atmosphere

    • Vertical transport of heat via rising warm air and sinking cooler air.
    • Diagrams illustrate hot air rising from surfaces and cooler air sinking.
    • Horizontal transport of heat is called advection.

  • Radiation: the third mechanism of energy transfer

    • Radiation does not require a medium; can occur through vacuum (e.g., Sun → Earth).
    • Emission of energy by all bodies depending on temperature.

  • Radiation: key characteristics

    • Wavelength: distance between wave crests (affects type of radiation).
    • Amplitude: height of the wave (relates to intensity).
    • Wave speed: constant (in vacuum) and equal to the speed of light, $$c \