Heating the EarthHeating the EarthAir PressureAir Pressure

Energy From the Sun

Where We Get Our Where We Get Our EnergyEnergy

• The Sun is a major source of energy for Earth.

• You can feel the radiant energy warming your skin

• Radiation- movement of energy through empty space

Sun’s EnergySun’s Energy

Absorption of EnergyAbsorption of Energy

• Dark surfaces absorb light, and it is usually changed into heat

• Surfaces that reflect light, such as white, remain cooler

ConductionConduction• The troposphere is heated by moving

heat through matter

• How does heat move through a metal pan?

• Conduction- heat moves from an area of higher temperature to area of lower temperature

RadiationRadiation

• Radiant energy travels from the Sun through space in waves

• Radiation passes easily through the atmosphere to the surface

• Surface radiates most back into atmosphere

ConvectionConvection• Transfer of heat within a liquid or gas

• As air heats it expands, becomes lighter

• Warm air becomes lighter than cool air, so warm air rises

• Cooler, denser air sinks

Forms of EnergyForms of Energy

• Let’s look at this animation for radiation, conduction, and convection

• http://www.wisc-online.com/Objects/ViewObject.aspx?ID=SCE304

What is Air Pressure?What is Air Pressure?

• Pressure- the amount of force per unit of area

• Weight- weight (force) is measured in Newtons

• Ex.- Holding a book (pg. 260)• Force over small area causes more

pressure than a large area

Air Pressure in Air Pressure in AtmosphereAtmosphere

• Air molecules are in constant motion and pulled toward Earth’s center by gravity

• Force of all the molecules moving causes air pressure

• Air pressure is greatest near surface

ElevationElevation

• What happens to air pressure as elevation changes?

• Air pressure decreases as distance above surface increases

• Very little weight of air pressing down

Water VaporWater Vapor

• Water evaporates from lakes, rivers, and oceans

• Water vapor molecules are lighter than other gas molecules

• So, more water vapor in air, the lower the air pressure

Measuring Air PressureMeasuring Air Pressure• Barometer- air pressure is measured

with this instrument

• Air pressure pushes down on the surface of the mercury in the containter

• Standard air pressure- 760 mm of mercury or 1 atmosphere or 1,013.20 mb

BarometersBarometers

How do Winds Form?How do Winds Form?• Wind- the horizontal movement of air

along Earth’s surface

• Earth’s atmosphere is always in motion

• Winds form as cool, heavy air moves toward warm, light air

• Cool air moves along the surface toward warmer air

How do Winds form?How do Winds form?• Winds are also caused by differences

in air pressure

• Cold, heavy air have high air pressure (Highs)

• Warm, light air have low air pressure (Lows)

• Speed of wind depends on the differences in air pressure

Air CurrentsAir Currents

• Air currents- up-and-down movements of air

• Some areas of Earth are warmed more than others

• Warmer air expands, becomes less dense

• Figure 11-21 pg. 266

Global WindsGlobal Winds

• Winds blow from regions of high pressure to regions of low pressure

• Differences in air pressure produce patters of global winds

• Large wind systems that circle the Earth

Global WindsGlobal Winds

• At the equator, warm air rises and moves toward the poles

• At the poles, cool air sinks and moves toward the equator

• Why do we receive cold winds during the winter in Nebraska?

Coriolis EffectCoriolis Effect• Winds curve as they move from high-

to low-pressure regions

• Winds toward equator curve to the west in the Northern Hemisphere

• Winds toward poles curve to the east

• Wind directions are reversed in Southern Hemisphere

Coriolis EffectCoriolis Effect

Trade WindsTrade Winds

• Prevailing pattern of easterly winds

• Found mainly in the tropics

• Responsible for steering tropical storms in the southern hemisphere

Prevailing WesterliesPrevailing Westerlies

• Blow strongest between 35-65 degrees latitude

• Felt strongest during winter seasons

• Blow from west to east

• Responsible for steering cyclones

Polar EasterliesPolar Easterlies

• Cold, dry winds that blow at high latitudes

• Blow from east to west

• Often weak and irregular winds

Sea and Land BreezesSea and Land Breezes

• All winds are caused by temperature differences and changes in air pressure

• Breeze coming from the sea toward the land is a sea breeze

• Breeze coming from the land toward the sea is a land breeze

Sea BreezeSea Breeze

• During the day, air over land is warmer and lighter than air over water

• The cooler, heavier air over the ocean moves in toward the land

• The result is a sea breeze

Sea BreezeSea Breeze

Land BreezeLand Breeze• At night, land cools faster than water

• Air over land becomes cooler than the air

• Heavier air over the land moves toward the water

• Warmer, lighter air rises over the land

Land BreezeLand Breeze