Solar Energy and the Atmosphere

Earth-Sun Relationships

Earth’s Motions• Earth has two principal motions—rotation and

revolutionEarth’s Orientation (tilt)• Seasonal changes occur because Earth’s

position relative to the sun continually changes as it travels along its orbit

Energy Transfer as HeatThree mechanisms of energy transfer:Conduction is the transfer of heat through matter

by molecular activityConvection is the transfer of heat by circulation

within a substance.Radiation is the transfer of energy (heat) through

space by electromagnetic waves that travel out in all directions

What Happens to Solar Radiation?

• Scattering:–Clouds, dust and gas reflect and bend light

rays; light rays are sent out in all directions–Causes sky to appear blue (blue light is more

easily bent)– Sunsets appear red because longer

wavelengths (red) are able to reach the surface (we are looking through more atmosphere on the horizon)

What Happens to Solar Radiation?

• Reflection:–20% of solar radiation is absorbed by the

atmosphere–50% is absorbed by the surface–30% is reflected back into space–Albedo: fraction of solar radiation that is

reflected back into space. – Earth’s albedo is 0.3

What Happens to Solar Radiation?

Absorption & Infrared Energy:• As the surface absorbs radiation, it heats up and

releases IR radiation• IR radiation is trapped by water vapor and CO2 in

the atmosphere• This process is called the greenhouse effect

What Happens to Solar Radiation?

Why Temperatures VaryFactors include:• latitude • heating of land and water, • altitude• geographic position• cloud cover• ocean currents

Fig. 7-7, p. 145

Prevailing winds pick up moisture from an ocean.

On the windward side of a mountain range, air rises, cools, and releases moisture.

On the leeward side of the mountain range, air descends, warms, and releases little moisture.

Latitude

Tropical Forest

Deciduous Forest

Coniferous Forest

Tundra (herbs, lichens, mosses)

Polar ice and

snow

Fig. 7-9, p. 147

ElevationMountain ice and snowTundra (herbs, lichens, mosses)Coniferous Forest

Deciduous ForestTropical Forest

Stepped Art

Factors Affecting Wind

• Wind is the result of horizontal differences in air pressure. Air flows from areas of higher pressure to areas of lower pressure

• The unequal heating of Earth’s surface generates pressure differences

• Three factors combine to control wind: pressure differences, the Coriolis effect, and friction

Factors Affecting Wind

Pressure Differences• A pressure gradient is the amount of pressure

change occurring over a given distance• Isobars are lines on a map that connect places

of equal air pressure• Closely spaced isobars indicate a steep pressure

gradient and high winds

Factors Affecting Wind

Coriolis Effect• The Coriolis effect describes how Earth’s

rotation affects moving objects. • In the Northern Hemisphere, all free-moving

objects or fluids, including the wind, are deflected to the right of their path of motion.

• In the Southern Hemisphere, they are deflected to the left

Factors Affecting Wind

Friction • Friction acts to slow air movement, which

changes wind direction• Jet streams are fast-moving rivers of air that

travel in a west-to-east direction (120 - 240 km/hour); little friction

Global Winds

• Convection Cells:–Warm air rises near the equator–Cooler air from the north replaces it at the

surface–The warm air that rose flows northward

and downward as it cools–The convection cells are called Hadley Cells

Fig. 7-4, p. 143

Heat released radiates to spaceCool, dry

air

Condensation and precipitation

Falls, is compressed, warms

Rises, expands, cools

Warm, dry air

Hot, wet air

Flows toward low pressure, picks up moisture and heat

HIGH PRESSURE Moist surface warmed by sun

LOW PRESSURE

LOW PRESSURE HIGH PRESSURE

Global Winds

Fig. 7-6, p. 144

Moist air rises, cools, and releases moisture as rainPolar cap

Arctic tundraEvergreen coniferous forest60°

Temperate deciduous forest and grassland

30°Desert

Tropical deciduous forest

Equator 0° Tropical rain forest

30° Desert

60°Temperate deciduous forest and grassland

Tropical deciduous forest

Polar cap

Fig. 7-8, p. 146

Fig. 7-10, p. 147

Cold Polar

TundraSubpolar

TemperateConiferous forest

Desert

Deciduous forest

GrasslandChaparral Tropical

Hot

DesertWet Rain forest Savanna

Tropical seasonal forest

Dry

Scrubland

Trade Winds• Winds that blow out of the east between 0-

30° latitude

Westerlies• Winds out of the west; between 30-60°

Polar Easterlies• Winds out of the east; from 60-90°

Global Winds

The Doldrums:• Equatorial “Low”• Little or no winds“Horse” Latitudes:• 30° latitude: sub-tropical high• Little or no winds

CURRENTS

Fig. 7-5, p. 143

Warm, less salty, shallow current

Cold, salty, deep current

Fig. 7-2, p. 142