WindWind

Wind is the general horizontal motion Wind is the general horizontal motion of air from one location to another of air from one location to another based on differences in air pressurebased on differences in air pressure

Air speed is measured by an Air speed is measured by an anemometeranemometer

Air movement is governed primarily by Air movement is governed primarily by Pressure gradient forcePressure gradient force Coriolis forceCoriolis force Friction forceFriction force

What causes wind What causes wind movementmovement

Direction is governed by the path of Direction is governed by the path of least distance between high pressure least distance between high pressure and low pressureand low pressure Pressure gradientPressure gradient

Speed will increase if there is a larger Speed will increase if there is a larger difference between pressuresdifference between pressures Steep pressure gradientSteep pressure gradient

RESULTANT WINDRESULTANT WIND

FUNCTION OF 3 THINGSFUNCTION OF 3 THINGS PGF + CF + FRICTIONPGF + CF + FRICTION

PGF AND CF ARE AT ODDSPGF AND CF ARE AT ODDS FRICTION DEFLECTS WINDS FRICTION DEFLECTS WINDS

SLIGHTLY IN FAVOR OF PGFSLIGHTLY IN FAVOR OF PGF

WHAT HAPPENS IN THE UPPER WHAT HAPPENS IN THE UPPER ATMOSPHERE?ATMOSPHERE?

BIRD’S EYE VIEW NORTHERN HEMISPHERE

LH

Pressure gradient

H L

Pressure gradientPressure gradient

The Coriolis EffectThe Coriolis Effect

When wind moves from zones of high When wind moves from zones of high pressure to zones of low pressure it pressure to zones of low pressure it veers due to earth rotationveers due to earth rotation To the right in the northern hemisphereTo the right in the northern hemisphere To the left in the southern hemisphereTo the left in the southern hemisphere

Equator faster rotation than the Equator faster rotation than the polespoles Demo –Demo – http://www.classzone.com/books/earth_shttp://www.classzone.com/books/earth_s

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Remembering the Remembering the direction of bend in the direction of bend in the

coriolis effectcoriolis effectBends to the rightBends to the right

Bends to the leftBends to the left

Effect of coriolis forceEffect of coriolis force

Strongest at higher latitudesStrongest at higher latitudes Weakest at the equatorWeakest at the equator The effect of coriolis increases with The effect of coriolis increases with

increasing windspeedincreasing windspeed The combined effect of coriolis and The combined effect of coriolis and

pressure gradient force makes winds pressure gradient force makes winds travel parallel to isobars = travel parallel to isobars = Geostrophic WindGeostrophic Wind

Friction forceFriction force

Effects of surface friction occur to ~ Effects of surface friction occur to ~ 5000 ft above the ground5000 ft above the ground

Cause winds to slow down and Cause winds to slow down and generally move across isobarsgenerally move across isobars

More pronounced when wind speeds More pronounced when wind speeds are higherare higher