Global WindsUnit 5: Sixth Grade

http://www.youtube.com/watch?v=uBqohRu2RRk

https://games.ciconline.org/windward/content/sailing.html#record

Windward Online Sailing around the world game

Whooosh!!!!!

When you open the valve on a bicycle tube, the air rushes out.

Why? The air inside the tube is

at a higher pressure than the air outside the tube.

This is similar to how winds are formed!

Wind

The movement of air cause by differences in air pressure is called wind

The greater the pressure difference, the faster the wind moves.

Rising and Sinking

Differences in air pressure are generally due to the unequal heating and temperature differences o f the earth.

Remember, warm air is less dense and will rise.

Cool air is more dense and sinks

Air Rises at the Equator

The equator receives more direct solar energy (radiant heating) than other latitudes, so air at the equator is warmer and less dense than the surrounding air. Lighter, one blanket

Warm, less dense air rises and creates an area of low pressure.

This warm, rising air flows toward the poles.

Air Sinks at the Poles

However, at the poles, the air is colder and denser than the surrounding air, so it sinks. Heavier, many blankets

This sinking air creates an area of high pressure around the poles

This cold polar air then flows toward the equator

Air blows from high to low!!

Low Pressure Rising, warmer air

Moist: Clouds, rain, snow, strong winds, warmer air

Snow means low!

High Pressure Sinking, colder air

Dry: Clear skies, sunshine, cool air, little wind

High and Dry!

You may imagine that wind moves in one huge, circular pattern from the poles to the equator.

In fact, air travels in many large circular patterns called convection cells Convection = circulation (moving air)

These convection cells are separated by pressure belts, which are bands of high or low pressure.

These belts are found about every 30* latitude

Pressure Belts

Pressure Beltshttp://www.youtube.com/watch?v=v7CaZOTXCSo

Pressure Belts

As warm air rises over the equator and moves toward the poles, the air begins to cool.

At about 30* North and 30*South latitude, some of this cool air begins to sink

Pressure Belts

This cool sinking air, causes high pressure around 30* N and S latitude.

This cooled air flows back to the equator, where it warms again, and rises.

And the same thing is happening at the poles, just in reverse!

At the poles, the cold air sinks, and moves toward the equator.

The air warms as it moves toward the equator.

Around 60* N and S latitude, the warmer air rises, which creates a low pressure belt.

This air then flows back to the poles

The Coriolis Effect

Pressure differences cause the air to move between the equator and the poles.

But due to the earth’s rotation, the air does not move in straight lines!

This apparent curving of the path of winds is called the Coriolis Effect.

Coriolis Effect

Because of the Coriolis Effect, winds traveling north in the Northern Hemisphere curve to the east, and winds traveling south curve to the west.

How would the Southern Hemisphere compare?

http://www.phschool.com/atschool/phsciexp/active_art/global_winds/index.html

The combination of convection cells found at every 30* latitude and the Coriolis Effect produces patterns of air circulation called Global Winds.

The major global wind systems are the Polar Easterlies, Westerlies, and Trade Winds.

Winds such as the Easterlies and Westerlies are named for the direction from which they blow

Global Winds

Polar Easterlies

The wind belts that extend from the poles to 60* latitude.

They are formed when cold, sinking air (high pressure) moves from the poles toward 60* north and south latitude

Polar Easterlies can carry cold, arctic air over the US, producing snow and freezing weather

Westerlies

The wind belts found between 30* and 60* latitude.

They flow toward the poles from west to east.

Can carry moist air, producing rain or snow (low pressure)

Trade Winds

Winds that blow from 30* latitude almost to the equator are the trade winds.

They are warm, steady breezes that blow almost continuously (low pressure).

The Coriolis Effect makes the trade winds appear to be curving to the west in the Northern Hemisphere

The Doldrums

The trade winds of the N and S 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.

Doldrums means “dull” or “sluggish”

The Horse Latitudes

At about 30* N and S latitude, sinking air creates an area of high pressure.

The winds at these locations are weak.

Most of the world’s deserts are located here because the sinking air is very dry

Jets Stream

Jet streams are narrow belts of high-speed winds that blow in the upper troposphere and lower stratosphere.

They can blow as fast as 400 km/hr

They do not follow regular paths around the earth.

They help pilots and meteorologists

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

Local geographic features, such as a shoreline or a mountain can produce temperature differences that can cause local winds

Local Winds

Sea Breezeshttp://www.youtube.com/watch?v=gM0d3fGew-0&feature=related

Land Breeze

At night, the land cools of faster than the sea. Cooler air descends creating an area of high

pressure. Wind blows from land to sea.

Sea Breeze During the day, land

gets hotter faster. Hot air rises, creating an

area of low pressure. Wind blows from the sea

to the land

Local Winds

• Land heat and cools more rapidly than does the sea. • Water retains heat longer than does land, and also takes

longer to heat and cool. The ocean regulates temperatures of coastal lands because oceans change temperature slowly.

• This causes temperature differences between land sea.

Mountain and Valley Breezes

So why is coastal Georgia usually warmer than Douglasville in winter?