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Heating Earth’s Surface and
Atmosphere Chapter 2

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2.1 Earth-Sun Relationship

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Earth-Sun Relationships
Earth’s two principal motions:
 Rotation is the spinning of the earth on its axis,
resulting in the daily cycle of day and night.
 Revolution is the movement of the Earth in an
elliptical orbit around sun, producing one year.
 Its perihelion, the closest point to sun occurs
on about January 3.
 The aphelion, which is the furthest point from
sun occurs on about July 4.

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Earth-Sun Relationships
What causes the seasons?
 The gradual change in day length accounts for
some of the differences in the seasons.
 A change in angle of the sun (altitude) also
plays a significant role.

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Earth-Sun Relationship
When the sun is directly overhead (at 90°) the
solar rays are more concentrated and more intense
The angle of the sun determines the path solar rays
take as they pass through the atmosphere
 At 90° rays travel the shortest path to the surface
 At lesser angles the rays have farther to travel and
more rays get dispersed

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Earth-Sun Relationships
Earth’s orientation

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Earth- Sun Relationship

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Earth-Sun Relationships
 Solstices:
 The summer solstice occurs on or about June 21 or 22.
 At that time, the sun’s rays are vertical on the Tropic of
Cancer. (23 ½° north latitude)
 It also produces the longest day in the northern
hemisphere.
 The winter solstice occurs on or about December 21 or
22.
 The sun’s rays are then vertical on the Tropic of
Capricorn. (23 ½° south latitude)
 This results in the shortest day in the northern
hemisphere.

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Earth-Sun Relationships
 Equinoxes:
 Equinox means that day and night are equal.
 The autumnal (fall) equinox happens on or about
September 21 or 22.
 The vernal (spring) equinox occurs on or about
March 21 or 22.
 The sun’s rays are vertical on the equator. (0°)
 Earth isn’t tilted away or towards the sun

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Earth-Sun Relationships

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2.2 Energy, Temperature and Heat

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Energy, Temperature, and Heat
Energy is the capacity to do work.
2 forms of energy:
 Kinetic energy describes an object in motion:
the faster the motion, the greater the energy.
 Potential energy means that an object is capable
of motion or work. Substances such as food,
gasoline, or wood contain potential energy.

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Energy, Temperature, and Heat
Temperature:
 Temperature is a measure of the average kinetic
energy of atoms or molecules in a substance.
 As temperature increases, energy is gained.
 Because the particles move faster
 As temperature decreases, energy is lost.

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Energy, Temperature, and Heat
Heat:
 Heat is the energy transferred in or out of object
due to temperature differences.
 Energy absorbed but with no increase in
temperature is called latent heat.
 Sensible heat is heat we can feel or measure
with a thermometer.

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2.3 Mechanisms of Heat Transfer

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Mechanisms of Heat Transfer
 Conduction:
 Conduction is the heat transferred through molecular and
electron collisions from one molecule to another.
 Metals are good conductors
 Convection:
 Convection is the heat transferred via movement or
circulation of a substance, primarily vertically
 Warm air rising creates thermal currents.
 Advection describes the primarily horizontal component
of convective flow.

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Mechanisms of Heat Transfer
Radiation

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Mechanisms of Heat Transfer
 Solar
radiation travels through space providing light
and heat energy.
 Wavelength describes the length of the crest of one radio
wave to the next.
 Visible light, often referred to as “white light,” actually
describes the sensitivity of the human eye to a range of
wavelengths.
 Infrared radiation cannot be seen by the human eye, but is
detected as heat.
 Ultraviolet radiation, on the opposite side of the visible
range, consists of wavelengths that may cause sunburns.

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Mechanisms of Heat Transfer
Laws of radiation:
1. All objects continually emit radiate energy of
a range of wavelengths.
2. Hotter objects radiate more total energy per
unit than colder ones.
3. Hotter objects radiate more short wave
radiation than cooler ones.
4. Objects that are good absorbers of radiation
are also good emitters.

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2.4 What Happens to Incoming
Solar Radiation?

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What Happens to Incoming
Solar Radiation?
 Reflection:
 Lightbounces back from an object at the same
angle and intensity.
 Scattering:
 Scatteringproduces a large number of weaker rays
traveling in different directions.
 Backscattering:
 Scattering,
both backwards and forwards, is known
as backscattering.

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What Happens to Incoming
Solar Radiation?
Reflection and the Earth’s albedo:
 Albedo is the % of radiation reflected by an
object.
 The albedo for Earth is about 30%.
 For the moon, the albedo is about 7%.
 Light objects have higher albedos and darker
objects have lower albedos.

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What Happens to Incoming
Solar Radiation?

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What Happens to Incoming
Solar Radiation?
Diffused light:
 Diffused light is the result of dust particles and
gas molecules scatter light in different
directions.
 This diffusion results in clear days with a bright
blue sky.
 A red sun on the horizon is the result of the
great distance solar radiation must travel before
it reaches your eyes.

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2.5 The Role of Gases in the
Atmosphere

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The Role of Gases in the Atmosphere
Heating of the atmosphere
 When gas molecules absorb radiation,
this energy is transformed into internal
molecular motion, detected as a rise in
temperature

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The Role of
Gases in the
Atmosphere

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The Role of Gases in the Atmosphere
The greenhouse effect:
 The greenhouse effect is a natural phenomenon
and is a result of the Earth’s atmosphere
trapping some outgoing radiation.
 Carbon dioxide and water vapor absorb
longwave radiation, which heats the air.
 The greenhouse effect is NOT the same as
global warming.

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The Role of Gases in the
Atmosphere

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2.6 Earth’s Heat Budget

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Earth’s Heat Budget
Annual energy balance:
 Incoming and outgoing radiation account for the
Earth’s heat budget.
 Figure 2-23 on page 56 (on next slide)

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Earth’s Heat Budget
 Latitudinal heat balance:
 Balance of incoming and outgoing radiation
applicable for whole earth is not maintained on
latitudes.
 At 38°, incoming radiation and outgoing radiation are
equal.
 Above 38°, the atmosphere loses more radiation.
 Below 38°, the atmosphere gains more radiation.
 This
energy imbalance is what drives winds and
ocean currents.