WindsWinds

Wind is the Wind is the horizontalhorizontal movement of air from movement of air from an area of an area of highhigh pressure to an area of pressure to an area of lowlow

pressure.pressure. All winds are caused by All winds are caused by

differences in differences in air air pressurepressure

Most differences in air Most differences in air pressure are due to pressure are due to unequal unequal heatingheating in the in the atmosphereatmosphere

Water has a higher Water has a higher specific heatspecific heat than sand, than sand, so it heats much slower.so it heats much slower.

CoolCool, dense air sinks , dense air sinks and has higher air and has higher air pressurepressure

WarmWarm, less dense air , less dense air rises and has lower rises and has lower pressurepressure

Why Air Moves Air Rises at the Equator

and Sinks at the Poles As the cold air sinks, it creates areas of high pressure around the poles. This cold polar air then flows toward the equator.

Pressure Belts Are Found Every 30º Convection cells are separated by pressure belts, bands of high and low pressure.

Global WindsGlobal Winds Caused by global Caused by global

convection currentsconvection currents.. They blow steadily from They blow steadily from

specific directions over specific directions over great distances.great distances.

The high pressure cool The high pressure cool air at the poles tries to fill air at the poles tries to fill in the low pressure areas in the low pressure areas at the equator.at the equator.

This causes the This causes the global global winds.winds.

This is why the weather This is why the weather systems tend to always systems tend to always come from west to east in come from west to east in Georgia.Georgia.

Polar EasterliesPolar Easterlies

Wind belts that Wind belts that extend from the extend from the poles to poles to 6060°° latitudelatitude

Formed from cold Formed from cold sinking air moving sinking air moving from the poles from the poles creating creating cold cold temperaturestemperatures

WesterliesWesterlies

Wind belts found Wind belts found between 30between 30° ° and 60° latitudeand 60° latitude

Flow towards Flow towards the poles from the poles from west to east west to east carrying carrying moistmoist airair over the over the United StatesUnited States

Trade WindsTrade Winds

Winds that blow Winds that blow from from 3030° almost ° almost to the equatorto the equator

Called the trade Called the trade winds because of winds because of their use by their use by early early sailorssailors

Doldrums and Horse LatitudesDoldrums and Horse Latitudes

DoldrumsDoldrumsLocated along the Located along the

equator where equator where no no winds blowwinds blow because the warm because the warm rising air creates rising air creates and area of low and area of low pressurepressure

Horse LatitudesHorse Latitudes Occur at about 30Occur at about 30° north ° north

and south of the equator and south of the equator where the winds are where the winds are very weakvery weak

Most deserts on the Most deserts on the Earth are located here Earth are located here because of the because of the dry airdry air

Jet StreamJet Stream

The jet streams are The jet streams are narrow belts of narrow belts of high speedhigh speed windswinds that blow in the that blow in the upper upper tropospheretroposphere and lower and lower stratospherestratosphere

SeparatesSeparates warm warm air from cold airair from cold air

Pressure CellsPressure Cells

The earth is The earth is encircled by encircled by several broad several broad prevailing wind prevailing wind belts.belts.

The three The three primary primary circulation cells circulation cells are known as are known as the: the: HadleyHadley cell; cell; Ferrel Ferrel cell; and cell; and PolarPolar cell. cell.

Why Air Moves, continued• The Coriolis Effect

The apparent curving of the path of currents due to the Earth’s rotation is called the Coriolis effect.

• This causes winds to curve to the right in the northern hemisphere, and the opposite in the southern hemisphere.

Measuring WindsMeasuring Winds Winds are described by Winds are described by

their their directiondirection and speed and speed A wind A wind vanevane determines determines

wind directionwind direction The name of a wind is the The name of a wind is the

direction it is coming from direction it is coming from so a north wind is from so a north wind is from the the northnorth. It is headed to . It is headed to the the southsouth..

Wind speed is measured Wind speed is measured with an with an anemometeranemometer..

Local winds are. . .Local winds are. . .

Winds that blow over Winds that blow over shortshort distances distances

Caused by Caused by unequal unequal heating of the earth’s heating of the earth’s surface within a small surface within a small areaarea

This creates local This creates local convection currents.convection currents.

Form only when no winds Form only when no winds are blowing from far awayare blowing from far away

Sea BreezeSea Breeze In the morning the sand In the morning the sand

heats up much faster heats up much faster than the water, so the than the water, so the air above the sand is air above the sand is hotter.hotter.

Hotter air is less dense, Hotter air is less dense, so it rises.so it rises.

The cooler air over the The cooler air over the ocean will push in to ocean will push in to cause the hot air to rise.cause the hot air to rise.

So in the morning the So in the morning the wind is in your face as wind is in your face as you face the ocean.you face the ocean.

Sea Breeze 2Sea Breeze 2

1. Warm air 1. Warm air over land rises over land rises

2. Sea Breeze 2. Sea Breeze moves inland moves inland

3. Cumuli 3. Cumuli develop aloft develop aloft and move and move seaward seaward

4. Upper level 4. Upper level return land return land breeze breeze

5. Cool air 5. Cool air aloft sinks aloft sinks over water over water

6. Sea Breeze6. Sea Breeze

Land BreezeLand Breeze At night, the sand cools At night, the sand cools

very quickly, while the very quickly, while the ocean temperature ocean temperature changes very little.changes very little.

So the warm air over the So the warm air over the ocean rises, pushed up ocean rises, pushed up by the cooler air over the by the cooler air over the beach.beach.

So the wind will hit your So the wind will hit your back as you look out over back as you look out over the ocean at night.the ocean at night.

Land Breeze 2Land Breeze 2

1. Cool air over 1. Cool air over land sinks land sinks

2. Land Breeze 2. Land Breeze moves out over moves out over water water

3. Relatively 3. Relatively warmer water warmer water heats air which heats air which then rises then rises

4. Upper level 4. Upper level return sea breeze return sea breeze

5. Cool air over 5. Cool air over land sinksland sinks

Sea/Land BreezesSea/Land Breezes