Wind and Air Circulation

Wind is the horizontal movement of air parallel to Earth’s surface.

An anemometer is an instrument that measures wind speed.

Wind is caused by differences in air pressure – which in turn is caused

by changes in atmospheric conditions (Ex: water

vapor, temperature, etc…)

Air pressure gradient is the difference in air pressure over a specific distance.

An isobaric map illustrates the pressure gradient of an area.

When the air pressure gradient is steep, the

isobars are close together.

HIGH WINDS

When the air pressure gradient is gentle, the isobars are further apart.

LOW WINDS or NO WINDS

Wind Direction

Winds moves from areas of high pressure to areas of low pressure.

Due to the Coriolis Effect, the wind direction is deflected to the right in the Northern Hemisphere

and to the left in the Southern Hemisphere.

A weather vane (wind vane) is an instrument that determines the

direction of wind.

The weather vane will point in the direction that the wind is coming from.

The wind is coming from the northwest and is blowing to the southeast.

Convection CellsThe atmosphere is

heated by insolation. Due to the changes in intensity and duration of insolation, unequal

heating leads to difference in air

pressure.

This will lead to the creation of

convection cells – the rising of warm/less dense air and the

descending of cool/more dense air.

Regions where air comes together to

form a vertical current is called convergence.

Regions where air spreads away from a

vertical current is called divergence.

convergence

divergence

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A jet stream is a strong, easterly flowing wind found in the upper troposphere. Jet streams influence the formation and direction of weather patterns.

Jet Stream

Jet Stream

Jet streams help to steer

air masses and fronts.

Planetary Winds and Pressure Belts

How do the winds seem to blow?

Winds blow towards low pressure.

Winds blow away from high pressure.

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Planetary Winds and Pressure Belts

High Pressure

Low Pressure

Due to the Coriolis Effect, winds that move away from a high pressure belts are deflected to the right in the Northern

Hemisphere.

These winds would be deflected to the left in

the Southern Hemisphere.

These are known as planetary winds.

Pressure Belts

Planetary Winds

Planetary Winds and Pressure Belts

The position of Earth’s pressure belts and the

planetray winds that are created will change as different points of the Earth are exposed to

direct insolation during Earth’s revolution around

the Sun.

As a result, different locations on Earth’s

surface will experience seasonal shifts in weather

patterns.

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Weather Movement in the United States Generally speaking, weather patterns

move from the southwest to the northeast in the US due to the

southwest prevailing winds.

Surface Ocean Currents

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Surface ocean currents are caused by wind blowing over the oceans

thus transferring energy to it.

The direction of movement of these ocean currents is a

reflection of the Coriolis Effect (clockwise in

Northern Hemisphere and counterclockwise in Southern Hemisphere) and the landmasses

surrounding the oceans.

As is true of prevailing winds, the positions of surface ocean currents will change seasonally

due to different areas of Earth’s surface receiving maximum insolation as Earth revolves around

the Sun.

Weather Station Model

Wind Direction

The wind blows along the shaft.

The wind originates from the southwest and has a speed of

15 knots at this location.

Wind Speed

Whole feather = 10 knots

Half Feather = 5 knots

1 knot = 1.15 mi/hr