# Wind

Document Sample

```					Wind
Factors affecting wind
I.     Wind - is the result of horizontal differences in air
pressure.
1. Air flows from areas of higher pressure to lower
pressure.
2. Solar energy is the ultimate driving force of wind –
unequal heating of the earth surface will generate
these pressure differences.
3. Three factors that control wind
2.   Coriolis effect
3.   Friction
• Pressure-gradient starts the wind moving
– Difference between high and low pressure. Wind will travel
from areas of high pressure to areas of low pressure.

• Pressure differences create wind – the greater the
differences the greater the wind.

• Isobars-lines that connect places of equal air pressure.
– The space in-between these isobars is expressed as the
• Close isobars – step gradient (high winds)
• Wide isobars – gentle gradient (low winds)

Difference between high and low pressure. Wind will
travel from areas of high pressure to areas of low
pressure.

On a non-rotating planet the wind will travel directly
across isobars from areas of high pressure to areas of
low pressure.
Coriolis Effect
• Coriolis Effect – the deviation of fluids & winds to the right in the
northern hemisphere due to the rotation (spinning) of the Earth.

• Shift in Wind Direction due to the Coriolis Effect.
The deflection of the wind is always directed at right angles to the
direction of air flow due to the rotation of the earth.

Affects only wind direction, not wind speed.

Deflection is affected by wind speed (the greater the wind speed
the greater the deflection).

Is strongest at poles (the earth spins or rotates faster at the poles
then at the equator) and weakest at equator.
Examples of the Coriolis Effect

Notice the deflection that takes place due to
the rotation of the Earth.
Examples of the Coriolis Effect

Notice the deflection that takes place due to
the rotation of the Earth.
How does the Coriolis Effect, effect the
movement of wind (air)?

In the diagram above, the Pressure Gradient Force
will start the wind moving from areas of high
pressure to areas of low pressure.

The Coriolis Effect will deflect or pull the wind to
the right in the Northern Hemisphere and to the
left in the Southern Hemisphere.

The actual path or direction of the wind has
changed.
Friction
• Friction only effects wind within a few
kilometers of Earth’s surface.
– Acts to slow air movement, which alters wind
direction.
What is a Geostrophic Wind?

The horizontal air pressure gradient causes air parcels to accelerate across isobars
from areas of high pressure toward areas of low pressure.

The Coriolis effect then deflects air parcels to the right in the Northern Hemisphere.

As the wind gains speed, the Coriolis effect increases in magnitude until it balances

The result is an un-accelerated horizontal wind blowing parallel to isobars that is called
the Geostrophic wind.
Jet Stream
The jet stream is the comparatively narrow current of air that moves around the Northern
and Southern Hemispheres of the Earth in wavelike patterns.

It can be compared to a "river" of wind moving at high speed.

The jet stream varies from about 100 to 400 miles (161 to 644 kilometers) wide and 1 to 3
miles (1.6 to 4.8 kilometers) thick.

Its strongest winds are generally encountered at about 30,000 feet (9,144 meters) in
altitude—in the troposphere.
The Jet Stream is created by the pressure
difference between the cold air (cP) in
Canada and warm air (cT) in the southwest
United States.
Surface Winds
Surface Winds are winds that come into connect with the Earth’s surface.
An example of a surface wind includes the Santa Ana Winds

The Santa Ana is a hot, dry, dusty wind in southwestern California that blows
westward through the canyons toward the coastal areas during spring and late fall.

The wind has its origin in the relatively stable, high-pressure weather system called
the Great Basin High that usually exists over southern Idaho, Utah, Nevada, and
eastern California
Surface Winds cont…
Surface Winds are winds that come into connect with the Earth’s surface

Examples of a surface wind includes a Chinook Wind

The orographic effect can leave lifted air to lose moisture and become drier and warmer.

This gives rise to the Chinook Wind effect (a U.S. term; called foehn winds elsewhere)
involving hot winds coming off the mountains.

When developed these can often be strong and may cause problems if fires occur in
timber and brush on the mountains.
Wind Farms