Convection in Our Atmosphere

Credit to: Burnett Middle School8th Grade Science

Previous KnowledgeWhat do you already know about convection?

CONVECTIONis the transfer of heat by the movement of warmed

matter (air or liquid)

The Sun provides the energy that drives convection within the atmosphere and

oceans, producing winds and ocean currents.

Hot Air is Less Dense!

Atmospheric Density

What is most dense

SINKS!

CONVECTION

CONVECTION

CONVECTION CURRENTSmove the air in our atmosphere!

We have global winds that blow because of these large convection currents

CONVECTIONWind over the shore changes

direction because of EARTH’S UNEVEN

WARMING & COOLING!

We can these local winds

Convection Currents

Click the Video button to watch a movie about

convection currents.

CONVECTIONDEMOS!

Tea baghttp://www.youtube.com/watch?v=YsCXw2bQU50&feature=youtu.be

Colored Waterhttp://www.youtube.com/watch?v=G9QJ1vv2WyM

http://www.youtube.com/watch?v=7xWWowXtuvA

Why are the heating elements placed beneath hot water tanks in people’s homes? Hot water rises.

So when the element heats the water, and the hot water rises, the water tank is filled with hot water.

Why does hot air rise and cold air sink?

Cool air is more dense than warm air, so the cool air ‘falls through’ the warm air.

Wind

Wind is the movement of air from an area of high pressure to an area of low pressure. This is caused by the unequal heating of the Earth’s surface.As air is heated, it becomes less dense and rises. The air pressure is also lower .Cooler, more dense air, has a higher pressure, and moves under the warmer air. This causes a convection current, creating windThe greater the pressure difference, the faster the air moves, and the stronger the wind blows.

How is Wind Measured?Wind direction is measured with a wind vane, which points in the direction the wind is coming from.This is how the wind is named. A western wind is blowing from the west.This means a northern wind actually blows toward the south.Wind speed is measured with an instrument called an anemometer.

Why We have Global WindsSince the air near the equator is less dense, it

rises forming areas of low pressure.The cold air near the poles sinks because it is

more dense, forming areas of high pressure.The air moves in large circular patterns

called convection currents.The change in density is due to

the unequal heating of Earth’s surface

Warm Moist Air Rises

Cool Dry Air Sinks

Cool Dry Air Sinks

Cold Moist Air Rises

Cold Moist Air Rises

Very Cold Air Sinks

Very Cold Air Sinks

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Wind Moves from HIGH

to LOW

Objects are

deflected to the

RIGHT in the

Northern

Hemisphere

But why?

The Coriolis EffectAs Earth rotates, the Coriolis effect turns winds in the Northern Hemisphere toward the right.

Northern Global Wind PatternsPolar Easterlies

90 – 60 latitude from the eastPrevailing Westerlies

60 – 30 latitude from the westTrade winds

30 – 0 latitude from the East

Global Winds• Polar Easterlies are the wind belts that extend from the poles to 60° latitude in both hemispheres. They form as cold, sinking air moves away from the poles. They can carry cold arctic air over the U.S. which can produce snow and freezing weather.

• Westerlies are the wind belts found between 30° and 60° latitude in both hemispheres. They blow toward the poles from west to east. These winds can carry moist air of the U.S. producing rain and snow.

• Trade Winds are the winds that blow from 30° latitude almost to the equator in both hemispheres. They curve to the West as they blow toward the equator.

Global Winds, continuedThe Doldrums The trade winds of the Northern and Southern Hemispheres meet in an area around the equator called the doldrums. there is very little wind because the warm, rising air creates an area of low pressure. The name doldrums means “dull” or “sluggish.”

Global WindsSailing the global winds activity

Jet StreamsNarrow belts of high-speed winds that blow

in the upper troposphere and lower stratosphere. Knowing the path of a jet stream is important not only to pilots but also to meteorologists. Because jet streams affect the movement of storms, meteorologists can track a storm if they know the location of a jet stream.

Jet StreamsJet Streams form at

latitudes where wind systems come together

High speed westerly winds form high above the surface

Local WindsLocal winds move over a short distanceCaused by the heating of a small area of Earth’s surface

Sea Breeze•The sun warms the land faster than the water, so the air above the land becomes warmer. •The cooler air over the water moves inland

Land Breeze•At night, the land cools faster than the water, so the air above the land becomes cooler.•The cooler air over the land moves out to the water.

Local Winds

• Local winds generally move short distances and can blow from any direction.

• Mountain and valley breezes are examples of local winds caused by an area’s geography.

• Sea and land breezes are affected by temperature.

Air CurrentsUnited streaming video – 11 minutes