24.3 solar energy and winds about half of the sunlight that reaches earth is absorbed by the...

24.3 Solar Energy and Winds

About half of the sunlight that reaches Earth is absorbed by the surface. The rest is either reflected back into space or absorbed in the atmosphere.

20% of incoming sunlight absorbed by clouds and gases

50% absorbed by surface

5% reflected by surface

25% reflected by clouds, dust, and gases


What happens to the energy Earth receives from the sun?

Energy in the Atmosphere

Some solar energy that reaches Earth’s atmosphere is reflected back, some is absorbed by the atmosphere, and some is absorbed by Earth’s surface.


How is energy transferred within the troposphere?


Energy is transferred within the troposphere in three ways: radiation, convection, and conduction.


About 30 percent of the incoming solar energy is reflected back into space by clouds, dust in the air, gases, and Earth’s surface.

About 20 percent of the sun’s energy is absorbed by clouds and gases.

About half of the solar energy passes through the atmosphere and is absorbed by the surface.



The atmosphere is heated primarily by energy that is reradiated by Earth’s surface.

• The energy radiated back into the atmosphere is mostly infrared radiation.

• Gases in the atmosphere, including water vapor and carbon dioxide, allow visible light to pass through but absorb most infrared radiation.



• These gases radiate some of this absorbed energy back to Earth’s surface, warming the lower atmosphere in a process called the greenhouse effect.

• Without the greenhouse effect, Earth’s surface would be much cooler than it is.



When Earth’s surface is heated, much of this energy is radiated back as infrared radiation.


Solar radiation

Infraredradiation


Energy is transferred within the troposphere.• Radiation from the sun heats Earth’s surface,

which then radiates heat skyward.• The air in direct contact with Earth’s surface is

heated by conduction. • Warm air near the surface expands and rises,

and cooler, denser air sinks, forming convection currents that move heat through the troposphere.



Energy in the AtmosphereA. Radiation Much of the sun’s

radiation reaches Earth’s surface, where it heats the land and water. Land and water radiate heat back into the atmosphere.

B. Conduction The conduction process transfers heat from land and water directly to the few meters of air nearest Earth’s surface.

C. Convection Convection moves heat through the troposphere. As surface air is heated by radiation and conduction, rising warm air is replaced by denser, downward-flowing cool air.

A

B

C


What causes winds?

Wind

Winds are caused by differences in air pressure.


Air naturally flows from areas of higher pressure to areas of lower pressure.

• This flow is wind, which is the mainly horizontal movement of air.

• Larger pressure differences produce stronger winds.

Wind


Differences in air pressure are often caused by the unequal heating of Earth’s surface.

• As air is heated, it expands.• As it becomes less dense, air rises.• Cooler, denser air flows in to replace it.• This process occurs on both local and global

scales, producing local and global winds.

Wind


What are some examples of local winds and global winds?

Local Winds

The breezes that occur where land meets a large body of water are examples of local winds.


On a hot summer day, there is often a cool breeze blowing in from the water to the beach. This breeze is an example of a local wind, a wind that blows over a short distance.

Local winds are caused by the unequal heating of Earth’s surface within a small region.

Local Winds


Water has a higher specific heat than land and takes longer to heat up and cool down.

• The sun heats the land more quickly than it heats the water.

• The air above the land becomes warmer than the air above the water.

• The warm air expands and rises. The cooler air over the water flows toward the land, creating a sea breeze.

Local Winds


At night, these temperature and pressure conditions are reversed.

• Land cools off more quickly than water. • The cooler air over land has a higher density

than the warmer air over water.• The result is a land breeze, where cooler air

over land moves toward water.

Local Winds


Sea breezes and land breezes are local winds.

Local Winds

Sea breeze Land breeze

Cooler air moving toward

the land

Warm air rising

Warm air rising

Cooler air moving toward

the water


What are some examples of global winds?

Global Winds

Trade winds, westerlies, and polar easterlies are examples of global winds.


Convection Cells

Winds that blow over long distances from a specific direction are called global winds.

• Global winds are caused by the unequal heating of Earth’s surface across a large region.

• Global winds move in a series of huge bands called convection cells.

Global Winds


Bands of wind are caused by temperature variations across Earth’s surface.

• At the equator, temperatures tend to be warmer than at other latitudes.

• Warm air rises at the equator, creating a low-pressure region.

• This warm air is replaced by cooler air brought by global winds.

• Higher in the atmosphere, air blows away from the equator toward the poles.

Global Winds


Earth is surrounded by a set of global wind belts.

Global Winds

Dry air sinks over the world’s deserts

Warm air rises at the equator until it reaches the top of the troposphere.

The circulating air patterns are called “convection cells.”

The area where the trade winds die out is known as the doldrums

Very cold air sinks at the poles and flows outward, creating winds called polar easterlies.

Earth’s rotation

Polar easterlies


The trade winds are wind belts just north and south of the equator.

In the Northern Hemisphere, they blow from the northeast to the southwest.

Global Winds


The prevailing westerlies occur between 30° and 60° latitude in both hemispheres. These winds generally blow from west to east over much of North America.

The polar easterlies extend from 60° latitude to the poles in both hemispheres.

Global Winds


For hundreds of years, sailing ships have relied on global winds to transport cargo across the oceans.

Global Winds


If Earth were not rotating on its axis, global winds would move in roughly straight paths from the poles to the equator.

The curving effect that Earth’s rotation has on all free-moving objects, including global winds, is called the Coriolis effect.

Global Winds


A. A rocket launched from the North Pole toward the equator would move in a straight line if Earth were not rotating.

B. The Coriolis effect causes such a rocket to appear to curve to the right.

Global Winds Non-rotating Earth

Movement ofrocket

Equator

Equator

Movement ofrocket

Direction of Earth’s rotation

Rotating Earth


Monsoons

Seasonal changes in the heating of Earth’s surface affect the circulation of the atmosphere.

• A monsoon is a wind system that is characterized by seasonal reversal of direction.

• Monsoons are similar to land and sea breezes except that they occur on a much wider scale and longer time frame.

Global Winds


Jet Stream

Global wind patterns are also affected by fast-moving streams of air at high altitudes.

• A belt of high-speed wind in the upper troposphere is called a jet stream.

• Jet streams are caused by great differences in air pressure that develop at high altitudes.

Global Winds


Assessment Questions

1. How does most of the heating of the atmosphere occur? a. solar energy reflected by the atmosphere

b. solar energy absorbed by the atmosphere

c. solar energy reflected from the land and oceans

d. solar energy absorbed then radiated by the surface



1. How does most of the heating of the atmosphere occur? a. solar energy reflected by the atmosphere

b. solar energy absorbed by the atmosphere

c. solar energy reflected from the land and oceans

d. solar energy absorbed then radiated by the surface

ANS: D



2. Which of the following types of wind is a local wind? a. trade windsb. jet streamc. land breezed. monsoon



2. Which of the following types of wind is a local wind? a. trade windsb. jet streamc. land breezed. monsoon

ANS: C

24.3 solar energy and winds about half of the sunlight that reaches earth is absorbed by the...

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