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Chapter 1
The Earth as a Rotating Planet
This chapter deals with the way solar radiation drives energy and matter flows in the
atmosphere and oceans and how these flows are linked to weather and climate. This
chapter introduces you to some basic ideas about the Earth, its rotation, and revolution.
 The Earth is shaped as an oblate ellipsoid because the Earth's rotation causes it to
bulge slightly at the equator.
 The Earth rotates on its axis in an eastward (retrograde) direction and revolves
(counterclockwise) around the sun .
 The Earth's rotation has three important environmental effects:
1. It imposes a daily, or diurnal, cycle of daylight, air temperature, air humidity, and
air motion.
2. It produces the Coriolis effect which deflects the flow of fluids (air and water) to
the right or left of their original path in the northern or southern hemisphere’s,
respectively.
3. As the Earth rotates, the combined effects of both the moon’s and suns’
gravitational pull on different sides of the Earth creates a rise and fall of ocean
water known as tides.
 The Geographic Grid provides a system for locating features on the Earth’s surface
using parallels of latitude and meridians of longitude.
 Latitude is the angular distance of a point north or south of the equator. It increases
from a minimum of 0° at the equator to a maximum of 90° at the north and the south
poles. Lines of latitude are parallel to each other and describe circles that decrease in
circumference away from the equator.
 Longitude is the angular distance of a point east or west of the prime meridian located
at Greenwich, England. It increases to the west and the east away from the prime
meridian (0°) to a maximum of 180°. 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.
 A map projection is a system that allows for the representation of a curved/spherical
geographic grid on a flat grid surface.
 Map scale relates measured distance on a map to actual distance on the Earth’s
surface.
 The polar projection (centered on either the north or south pole) produces a map with
true relative shapes and sizes of small areas.
 The Mercator projection portrays a rectangular grid of meridians as straight vertical
lines intersected by parallels as straight horizontal lines which represent the true
compass direction of any straight line on the map. Meridians are equally spaced but
parallels at higher latitudes. This map projection is particularly useful for showing the
flow of winds and ocean currents as well as lines of equal air temperature and
pressure.
 The Goode projection uses two sets of mathematical curves (sine curves and ellipses)
to depict meridians. This projection indicates the true sizes of geographical areas on
the Earth’s surface.
 The standard time system is based on twenty-four time zones that keep time
according to standard meridians that are spaced 15° apart and represent a time
difference of one hour.
 The international date line is located near 180° longitude. Crossing this line in a
westward direction requires the calendar to be advanced by one day.
 Daylight savings time is an adjustment of the clock during the longest daylight period
of the year (high sun season) to transfer the morning light to the early evening (to
allow society to benefit from longer summer evenings). Clocks are set one hour ahead
in the spring and returned to standard time in the autumn (set back by one hour).
 The Earth revolves counterclockwise around the sun every 365¼ days in an elliptical
orbit.
 The Earth is closest to the sun at perihelion (~ January 3) and farthest from the sun at
aphelion (~ July 4).
 The Earth’s axis of rotation is tilted 23½° away from the perpendicular (to the plane
of the ecliptic) and its north pole always points towards the North Star, Polaris.
 The Earth’s axial tilt in combination with the its revolution around the sun produce the
progression of the seasons.
 At an equinox (vernal equinox-March, autumnal equinox-September), everywhere
on Earth experiences a 12-hour day and a 12-hour night.
 At a solstice (June, December), polar regions experience either a 24-hour day or a 24hour night.
 The maximum solar radiation is received at the subsolar point which crosses the
equator twice in the course of a year as it moves between the Tropic of Cancer (23
½°N) to the Tropic of Capricorn (23 ½°S).
 Two important facts about the Sun-Earth energy flow system:
1. Half of the Earth is always receiving solar energy.
2. Solar energy is not received uniformly over the Earth’s surface.