Chapter 19 The Atmosphere in Chapter 19 The Atmosphere in MotionMotion

Page 412Page 412 What special gear is the hang glider What special gear is the hang glider

wearing?wearing? What force is keeping the hang glider aloft?What force is keeping the hang glider aloft? What other kind of activities depend on this What other kind of activities depend on this

force?force? What causes winds?What causes winds?

Chapter 19.1Chapter 19.1

Air Pressure and the WindAir Pressure and the Wind

What is air pressure?What is air pressure?

A column of air that reaches from sea level A column of air that reaches from sea level to the tom of the atmosphere pushes down to the tom of the atmosphere pushes down at 147lbs per square inchat 147lbs per square inch

Air pressureAir pressure – is the weight of the overlying – is the weight of the overlying atmosphereatmosphere

It is exerted in all directionsIt is exerted in all directions Force pushing on your body is balanced Force pushing on your body is balanced

by your body pushing outby your body pushing out

The higher you go into the atmosphere the lover thThe higher you go into the atmosphere the lover the pressuree pressure

Barometers – used to measure air pressureBarometers – used to measure air pressure– Aneroid – evacuated can with read outs Aneroid – evacuated can with read outs

attached and barographattached and barograph– Mercury p 414Mercury p 414

Units of air pressureUnits of air pressure– inches or millimeters – used to read mercuryinches or millimeters – used to read mercury– millibars used on weather maps – these are millibars used on weather maps – these are

adjusted to sea level pressure due to altitude adjusted to sea level pressure due to altitude differencesdifferences

Why does air pressure ChangeWhy does air pressure Change

Elevation – higher up less air pressureElevation – higher up less air pressure Temperature – the warmer (more spread Temperature – the warmer (more spread

out) the less Air P.out) the less Air P. Water Vapor – the more water vapor the Water Vapor – the more water vapor the

lower the A.P. – H2O molecules weigh lower the A.P. – H2O molecules weigh less than the N & O molecules in the airless than the N & O molecules in the air

Isobars – lines of equal pressure – closed Isobars – lines of equal pressure – closed isobar forms a closed lop on a mapisobar forms a closed lop on a map

If pressure increases toward center it is a If pressure increases toward center it is a High Pressure CenterHigh Pressure Center

Low pressure center – pressure is lowerLow pressure center – pressure is lower Pressure Gradient – how close the isobars Pressure Gradient – how close the isobars

are. Close together – large gradientare. Close together – large gradient

What makes the wind blowWhat makes the wind blow

Difference in A.P. – the greater the Difference in A.P. – the greater the difference the faster the winds. The closer difference the faster the winds. The closer the isobars the faster the windthe isobars the faster the wind

A wind blows form High P. to low P.A wind blows form High P. to low P.– e.g. Hot air on an island rises (form L.P.) Cool e.g. Hot air on an island rises (form L.P.) Cool

air from the water (H.P) rushes in, this is known air from the water (H.P) rushes in, this is known as a sea breezeas a sea breeze

Measuring surface wind direction Measuring surface wind direction and speed.and speed.

Wind vane – measure the direction Wind vane – measure the direction from from which the wind is blowing – which the wind is blowing – Winds are Winds are named by the direction they come fromnamed by the direction they come from– e.g. westerly or sea breezee.g. westerly or sea breeze

Anemometer – measure wind speedAnemometer – measure wind speed

Chapter 19.2Chapter 19.2

Factors affecting WindFactors affecting Wind

Coriolis EffectCoriolis Effect

If the earth did not spin and was perfectly smooth air would If the earth did not spin and was perfectly smooth air would flow strait from high pressure areas (poles) directly to low flow strait from high pressure areas (poles) directly to low pressure areas (equator)pressure areas (equator)

Coriolis effect causes objects traveling freely over the Coriolis effect causes objects traveling freely over the earth to curveearth to curve– In n. hemisphere curve rightIn n. hemisphere curve right– In s. hemisphere curve leftIn s. hemisphere curve left– The effect is greater near the polesThe effect is greater near the poles– The effect is also greater in long diastase travel vs. The effect is also greater in long diastase travel vs.

short travelshort travel– The effect increases with increased speedThe effect increases with increased speed

Friction – with the earth’s surface slows winds Friction – with the earth’s surface slows winds down. The smooth surface(water) the faster down. The smooth surface(water) the faster wind can blow the higher coriolis effectwind can blow the higher coriolis effect

The coriolis effect is a strong factor in determining The coriolis effect is a strong factor in determining wind direction as is a Pressure gradient speedwind direction as is a Pressure gradient speed

CoriolisCoriolis causes winds to blow counter clockwise in a low, causes winds to blow counter clockwise in a low, clockwise in highclockwise in high

Jet stream – swift winds due to low friction – direct Jet stream – swift winds due to low friction – direct path of stormspath of storms

Global Wind PatternsGlobal Wind Patterns

Non rotating earth Non rotating earth would allow warm air to rise at the would allow warm air to rise at the equator, move to the poles and sink to travel back to the equator, move to the poles and sink to travel back to the equatorequator, resulting in large circulation cell, resulting in large circulation cell

The coriolis effect (Rotation of earth) prevents this from The coriolis effect (Rotation of earth) prevents this from happeninghappening

3 cell circulation model3 cell circulation model Weakness of 3Celled modelWeakness of 3Celled model

– gives simplified view of circulation between 30gives simplified view of circulation between 30 and and 6060

– No effect given to continents or seasonNo effect given to continents or season– Simplifies upper level windsSimplifies upper level winds

B. Description of Wind and B. Description of Wind and Pressure BeltsPressure Belts

ITCZ (intertropical convergence zone) occurs at the ITCZ (intertropical convergence zone) occurs at the equatorequator– hot and humid with little or no windhot and humid with little or no wind– rain is commonrain is common– historically been called the doldrumshistorically been called the doldrums

Between 20Between 20 and 35 and 35 air sinks forming subtropical highs, air sinks forming subtropical highs, location of earth’s deserts. Known as horse latitudes location of earth’s deserts. Known as horse latitudes

Between the doldrums and the horse latitudes are the Between the doldrums and the horse latitudes are the easterly easterly trade windstrade winds– Warm and steady (speed and direction) windsWarm and steady (speed and direction) winds

Chapter 19.3Chapter 19.3

Continental and Local WindsContinental and Local Winds

Effects of Seasons and Effects of Seasons and continentscontinents

Seasons, land masses and topography causes Seasons, land masses and topography causes winds to vary from global patterns depicted in the 3 winds to vary from global patterns depicted in the 3 cell modelcell model

Hot air above land in summer creates low-pressure. Hot air above land in summer creates low-pressure. Cold air above oceans in summer creates high Cold air above oceans in summer creates high pressurepressure– e.g. Atlantic Highs bring winds off the ocean into e.g. Atlantic Highs bring winds off the ocean into

the eastern sea board. Winter is reversedthe eastern sea board. Winter is reversed Monsoons – winds caused by seasonal pressure Monsoons – winds caused by seasonal pressure

changes changes

Local winds – extent 100 km or less include Local winds – extent 100 km or less include sea breeze, land breeze, mountain breeze sea breeze, land breeze, mountain breeze

and valley breezeand valley breeze Sea – land breeze - During day land is waSea – land breeze - During day land is wa

rmer creating low pressure above` causes rmer creating low pressure above` causes the cool air (H) to blowing from the water (the cool air (H) to blowing from the water (sea) and night it reversesea) and night it reverse

Mountain Breeze – at night the air Mountain Breeze – at night the air against the mountain cools more than against the mountain cools more than the surround air and sinks down hillthe surround air and sinks down hill

Valley breeze – mountain heats the air Valley breeze – mountain heats the air causing it to rise and the air from the causing it to rise and the air from the valley flows up hillvalley flows up hill