Heating the Earth Air Pressure Energy From the Sun

Where We Get Our Energy 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 Energy

Absorption of Energy Dark surfaces absorb light, and it is usually changed into heat Surfaces that reflect light, such as white, remain cooler

Conduction 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

Radiation 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

Convection 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 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? 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 Atmosphere 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

Elevation What happens to air pressure as elevation changes? Air pressure decreases as distance above surface increases Very little weight of air pressing down

Water 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 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

Barometers

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? 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 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 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 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 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 Effect

Trade Winds Prevailing pattern of easterly winds Found mainly in the tropics Responsible for steering tropical storms in the southern hemisphere

Prevailing Westerlies Blow strongest between 35-65 degrees latitude Felt strongest during winter seasons Blow from west to east Responsible for steering cyclones

Polar Easterlies Cold, dry winds that blow at high latitudes Blow from east to west Often weak and irregular winds

Sea 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 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 Breeze

Land 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 Breeze