CH 2 - Heating the Earth's Surface and Atmosphere(1)

CH 2: HEATING EARTH'S SURFACE AND ATMOSPHERE

By Tom Carboni

Facts About Earth and Sun Scale

  • The Sun’s diameter is 109 times that of Earth.

  • Approximately 1.31 million Earths could fit inside the Sun.

  • Distance from Earth to the Sun: 93 million miles.

  • Light from the Sun takes 8 minutes and 20 seconds to reach Earth.

  • Sun’s corona temperature: ~3.5 million °F; core temperature can exceed 27 million °F.

Factors Affecting Temperature Distribution Across Planetary Surfaces

Solar Insolation vs Distance

  • Solar Irradiance (Insolation): Energy per unit time per unit area.

  • Distance from Sun (in 10^9 m) and corresponding irradiance values:

    • Mercury: 57, 9116.4 W/m²

    • Venus: 108, 2611.0 W/m²

    • Earth: 150, 1366.1 W/m²

    • Mars: 227, 588.6 W/m²

    • Jupiter: 778, 50.5 W/m²

    • Saturn: 1426, 15.04 W/m²

    • Uranus: 2868, 3.72 W/m²

    • Neptune: 4497, 1.51 W/m²

    • Pluto: 5806, 0.878 W/m²

  • Notes on energy intensity: Energy at twice the distance (3r) from the Sun is spread over four times the area, resulting in one-fourth the intensity.

Earth's Motions

  • Rotation: Earth spins on its tilted axis (23.5° tilt).

  • Revolution: Earth orbits around the Sun.

Perihelion and Aphelion

  • Perihelion: Point in orbit closest to the Sun.

  • Aphelion: Point in orbit farthest from the Sun.

  • Changes in distance from the Sun cause negligible radiation change at Earth’s surface.

Latitude and Longitude

Latitude

  • Latitude lines: Imaginary lines running east-west, measuring degrees north/south from the Equator.

Longitude

  • Longitude lines: Imaginary lines running north-south, measuring degrees east/west from the Prime Meridian.

  • Earth rotates 360° in 24 hours = 15° per hour (defining time zones).

Important Lines of Latitude

  • Significant parallels mark Earth’s tilt: 66.5°N, 23.5°N, 23.5°S, 66.5°S.

What Causes the Seasons?

  • Earth’s Tilt: The primary cause; alters sun's angle and energy absorption on Earth's surface throughout the year.

Seasonal Dynamics

  • Southern Hemisphere experiences winter when it is summer in the Northern Hemisphere.

Defining the Seasons

  • Equinox: March 21-22 and September 22-23. The sun is vertical at the equator.

  • Solstices: June 21-22 (Sun vertical at 23.5°N), December 21-22 (Sun vertical at 23.5°S).

Kepler’s Second Law

  • Celestial bodies sweep out equal areas in equal times, indicating variable orbit speeds and seasonal length based on eccentricity.

Earth-Sun Geometry

Solar and Zenith Angles

  • Solar Angle: Angle between surface and sun’s rays.

  • Zenith Angle: Angle between sun rays and the vertical.

Solstices and Equinoxes

  • Maximum and minimum daylight during solstices.

  • Equal daylight at equinoxes.

Calculating Angles

  • Solar Elevation Angle: 90° - (latitude - solar declination).

  • Zenith Angle: Difference between location latitude and solar declination.

  • Solar Declination: Latitude where sun rays are perpendicular.

Temperature and Heat

  • Temperature: Average kinetic energy of atoms/molecules.

  • Heat: Energy transferred due to temperature differences.

Latent vs. Sensible Heat

  • Latent Heat: Heat from phase changes.

  • Sensible Heat: Detectable heat without phase change.

Mechanisms of Heat Transfer

  1. Conduction: Heat transfer through molecular collisions.

  2. Convection: Heat transfer via fluid motion due to density changes.

  3. Radiation: Emission of energy as electromagnetic waves.

Solar Radiation

  • Travels through space as light and heat.

  • Wavelength: Distance between wave crests.

  • Types of Radiation: Visible light, infrared (heat), ultra-violet (can cause burns).

Radiation Laws

  • Stefan-Boltzmann Law: Energy emitted by a body per area is proportional to its temperature.

  • Wein’s Displacement Law: Inverse relationship between temperature and peak emission wavelength.

Incoming Solar Radiation Fate

  • Transmission: Energy passing through without reaction.

  • Absorption: Energy retained and re-emitted.

  • Reflection: Light bounces back at same angle.

  • Scattering: Weaker rays in various directions.

Greenhouse Effect

  • Greenhouse Gases: CO2 and H2O absorb and re-emit outgoing LW radiation, trapping heat.

  • Earth's average temperature would be 0°F without this effect, while it currently averages 59°F.

Energy Balance

  • Tropics have energy surplus; mid-latitudes and polar regions have deficits.

  • Energy transfer via global wind systems and ocean currents stabilizes average temperatures.

Solar Insolation and Latitude Effects

  • Solar insolation decreases from low to high latitudes.

  • Incoming solar radiation at Top of Atmosphere is greater than at the surface due to obstruction and absorption by the atmosphere.

Conclusion

  • Understanding mechanisms of heating Earth's surface and atmosphere is essential in grasping climate dynamics and energy balance.

End of Chapter 2 Material