Chapter 1 Notes: The Earth as a Rotating Planet

The Earth as a Rotating Planet

This chapter explores how solar radiation drives energy and matter flows in the atmosphere and oceans, linking these flows to weather and climate. It introduces fundamental concepts about the Earth, its rotation, and revolution.

Earth's Shape and Rotation

  • The Earth is an oblate ellipsoid, bulging at the equator due to its rotation.
  • The Earth rotates eastward (retrograde) and revolves counterclockwise around the sun.

Effects of Earth's Rotation

  • The Earth's rotation has three primary environmental effects:
    1. Diurnal Cycle: It creates a daily cycle of daylight, air temperature, humidity, and air motion.
    2. Coriolis Effect: It deflects the flow of fluids (air and water). In the Northern Hemisphere, deflection is to the right; in the Southern Hemisphere, it's to the left.
    3. Tides: The combined gravitational pull of the moon and sun on different sides of the Earth causes the rise and fall of ocean water, known as tides.

Geographic Grid

  • The Geographic Grid is a system for locating features on Earth using parallels of latitude and meridians of longitude.
Latitude
  • Latitude is the angular distance north or south of the equator.
    • It ranges from 0° at the equator to 90° at the North and South Poles.
    • Lines of latitude are parallel and form circles that decrease in circumference away from the equator.
Longitude
  • Longitude is the angular distance east or west of the prime meridian (Greenwich, England).
    • It increases from 0° at the prime meridian to 180° west and east.
    • Lines of longitude are farthest apart at the equator and converge at the poles.
    • All circles described by meridians of longitude have the same circumference.

Map Projections

  • A map projection is a system for representing the curved geographic grid on a flat surface.
Map Scale
  • Map scale relates measured distances on a map to actual distances on the Earth’s surface.
Polar Projection
  • The polar projection (centered on the North or South Pole) preserves the true relative shapes and sizes of small areas.
Mercator Projection
  • The Mercator projection displays meridians as straight, vertical lines and parallels as straight, horizontal lines.
    • It accurately represents the compass direction of straight lines.
    • Meridians are equally spaced, but parallels are more widely spaced at higher latitudes.
    • Useful for showing wind and ocean currents, as well as lines of equal air temperature and pressure.
Goode Projection
  • The Goode projection uses sine curves and ellipses to represent meridians.
    • It accurately shows the true sizes of geographical areas.

Time Systems

Standard Time
  • The standard time system is based on 24 time zones.
    • Each zone is 15° apart, representing a one-hour time difference.
International Date Line
  • The International Date Line is located near 180° longitude.
    • Crossing westward requires advancing the calendar by one day.
Daylight Saving Time
  • Daylight Saving Time adjusts the clock during the longest daylight period to shift morning light to the evening.
    • Clocks are set one hour ahead in the spring and back one hour in the fall.

Earth's Revolution and Seasons

  • The Earth revolves counterclockwise around the sun every 36514365\frac{1}{4} days in an elliptical orbit.
  • The Earth is closest to the sun at perihelion (around January 3) and farthest at aphelion (around July 4).
  • The Earth’s axis is tilted 2312°23\frac{1}{2}° from the perpendicular to the plane of the ecliptic.
    • The North Pole always points towards Polaris (the North Star).
  • The Earth’s axial tilt, combined with its revolution, causes the seasons.
Equinoxes
  • At an equinox (vernal in March, autumnal in September), all locations on Earth experience 12 hours of daylight and 12 hours of night.
Solstices
  • At a solstice (June, December), polar regions experience either 24 hours of daylight or 24 hours of night.
Solar Radiation
  • Maximum solar radiation is received at the subsolar point.
    • The subsolar point crosses the equator twice a year as it moves between the Tropic of Cancer (2312°N23\frac{1}{2}°N) and the Tropic of Capricorn (2312°S23\frac{1}{2}°S).
  • Important facts about the Sun-Earth energy flow system:
    1. Half of the Earth always receives solar energy.
    2. Solar energy is not received uniformly across the Earth’s surface.