Air Pressure and Winds

Air Pressure and Weather Air pressure is a

measure of how hard air is pushing on the ground

Barameter – measures this pressure

http://www.free-online-private-pilot-ground-school.com/images/mercurial-barometer.gif

Air Pressure and Weather Air pressure

decreases with altitude

Air Pressure and Weather Air pressure changes

daily Caused by changes in

air density related to temperature

Warm air is less dense than cooler air

Larger pressure changes occur as weather changes Used to forecast

weather

Air Pressure and WeatherThe FALL of the barometer (decreasing pressure) In very hot weather, the fall of the barometer denotes thunder. Otherwise, the sudden

falling of the barometer denotes high wind. In frosty weather, the fall of the barometer denotes thaw. If wet weather happens soon after the fall of the barometer, expect but little of it. In wet weather if the barometer falls expect much wet. In fair weather, if the barometer falls much and remains low, expect much wet in a few

days, and probably wind. The barometer sinks lowest of all for wind and rain together; next to that wind, (except it

be an east or north-east wind).The RISE of the barometer (increasing pressure) In winter, the rise of the barometer presages frost. In frosty weather, the rise of the barometer presages snow. If fair weather happens soon after the rise of the barometer, expect but little of it. In wet weather, if the mercury rises high and remains so, expect continued fine weather

in a day or two. In wet weather, if the mercury rises suddenly very high, fine weather will not last long. The barometer rises highest of all for north and east winds; for all other winds it sinks.The barometer UNSETTLED (unsteady pressure) If the motion of the mercury be unsettled, expect unsettled weather. If it stands at "MUCH RAIN" and rises to "CHANGEABLE" expect fair weather of short

continuance. If it stands at "FAIR" and falls to "CHANGEABLE", expect foul weather. Its motion upwards, indicates the approach of fine weather; its motion downwards,

indicates the approach of foul weather.

Air Pressure and Weather Falling air

pushes hard high pressure Compresses and

warms

Rising air doesn’t push as much low pressure Expands and

cools

Air Pressure and Weather Low pressure = rising air = expanding air = cooling

air= water condenses = clouds and precipitation

High pressure = falling air = compressing air = heating up = air holds more water = fair weather (hard for clouds to form)

Make a Barometer

“Dry” barometer

Construct in class – monitor every day for a week

“Wet” barometer

Wind

Air moves because the unequal heating and cooling of Earth (and the atmosphere)

Air moves from areas of high pressure (cool, sinking air) to areas of low pressure (warm, rising air) creates wind

http://www.rrbenergy.com/images/concept-wind.jpg

Land/Sea Breezes

Unequal heating of air over land and water result in breezes near shorelines

Land warm during day rises; cool sea breeze replaces rising air

Land cool during night air sinks; cool land breeze blows out to sea

See Animation

Global Air Movements

If Earth did not rotate and was all land or water – we’d have two big convection currents, one in the northern hemisphere, one in the southern

Air would heat up at equator, rise, cool down over poles and fall

Global Air Movements

However, Earth DOES rotate…

Results in Coriolis effect: Moving particles

deflect to the right in the northern hemisphere and the left in southern hemisphere

See Animation

Global Air Movements

Coriolis effect combines with heat imbalance to create global wind systems that transport colder air to warmer areas and vice versa balances Earth’s heat energy

Animate it!

L

H

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Jet Streams

Narrow bands of fast, high-altitude, westerly winds form between wind zones

Polar and Subtropical jet streams

Disturbances form along jet streams and cause large-scale weather systems

Weather systems follow jet stream

Position of jet streams varies

http://www.fas.org/irp/imint/docs/rst/Sect14/FIG07_014A.jpg

http://oceanservice.noaa.gov/education/yos/resource/JetStream/global/images/jetstream3.jpg

Jet Streams

Video Explanation

Jet Stream

Jet Stream