+

Heating Earth’s Surface and Atmosphere Chapter 2

+

2.1 Earth-Sun Relationship

+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.

+

+

+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.

+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 atmosphereAt 90° rays travel the shortest path to the surfaceAt lesser angles the rays have farther to travel and

more rays get dispersed

+Earth-Sun RelationshipsEarth’s orientation

+Earth- Sun Relationship

+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.

+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

+Earth-Sun Relationships

+

2.2 Energy, Temperature and Heat

+Energy, Temperature, and HeatEnergy, 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.

+Energy, Temperature, and HeatEnergy, 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.

+Energy, Temperature, and HeatEnergy, 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.

+

2.3 Mechanisms of Heat Transfer

+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 verticallyWarm air rising creates thermal currents.Advection describes the primarily horizontal component

of convective flow.

+Mechanisms of Heat Transfer

Radiation

+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.

+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.

+

2.4 What Happens to Incoming Solar Radiation?

+What Happens to Incoming What Happens to Incoming Solar Radiation?Solar Radiation?

Reflection:Light bounces back from an object at the same

angle and intensity.

Scattering:Scattering produces a large number of weaker rays

traveling in different directions.

Backscattering:Scattering, both backwards and forwards, is known

as backscattering.

+What Happens to Incoming What Happens to Incoming Solar Radiation?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.

+What Happens to Incoming What Happens to Incoming Solar Radiation?Solar Radiation?

+

+What Happens to Incoming What Happens to Incoming Solar Radiation?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.

+

2.5 The Role of Gases in the Atmosphere

+The Role of Gases in the Atmosphere

Heating of the atmosphereWhen gas molecules absorb radiation,

this energy is transformed into internal molecular motion, detected as a rise in temperature

+The Role of Gases in the Atmosphere

+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.

+The Role of Gases in the Atmosphere

+

2.6 Earth’s Heat Budget

+Earth’s Heat BudgetEarth’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)

+

+Earth’s Heat BudgetEarth’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.