Science NewsScience News

What is WIND?What is WIND?The horizontal motion of air The horizontal motion of air

across Earth’s surface; across Earth’s surface; movement produced by movement produced by

differences in air pressure differences in air pressure from an area of high pressure from an area of high pressure (warm air) to an area of low (warm air) to an area of low

pressure (cool air)pressure (cool air)

GLOBAL WINDSGLOBAL WINDS

Global WindsGlobal Winds

The atmosphere balances The atmosphere balances differences of unequal differences of unequal

heating by acting as a giant heating by acting as a giant heat-transfer system. This heat-transfer system. This

system moves warm air system moves warm air toward high latitudes and toward high latitudes and

cool air toward the equatorcool air toward the equator

GLOBAL Direction of GLOBAL Direction of WINDWIND

3 WIND SYSTEMS 3 WIND SYSTEMS “ZONES”“ZONES”

Polar easterliesPolar easterlies 60 DEGREES – POLES N & S 60 DEGREES – POLES N & S

LATITUDES LATITUDES

Dense cold air sinking from the Dense cold air sinking from the polar high toward the sub polar polar high toward the sub polar low. These winds are not low. These winds are not constant like the trade winds.constant like the trade winds.

WesterliesWesterlies 30 – 60 DEGREES N & S 30 – 60 DEGREES N & S

LATITUDES LATITUDES

Dominant and steady surface Dominant and steady surface wind moving west-to-east wind moving west-to-east towards the POLES. Move towards the POLES. Move much of the weather across much of the weather across USA & Canada.USA & Canada.

Trade windsTrade winds 30 degrees N – 30 degrees S 30 degrees N – 30 degrees S

LATITUDESLATITUDES

Two belts of winds, air in this Two belts of winds, air in this region sinks, warms and region sinks, warms and moves toward the equator in moves toward the equator in an easterly direction. an easterly direction.

Boundaries of Boundaries of Wind SystemsWind Systems

JET STREAM:JET STREAM: A narrow band of A narrow band of fast moving wind that varies with fast moving wind that varies with

seasonsseasons

Result of the difference between Result of the difference between

air masses (Temperature & air masses (Temperature & Pressure) at the wind zone Pressure) at the wind zone

boundaries. boundaries.

2 Types of 2 Types of JETSTREAMS JETSTREAMS Major Major

POLAR JET STREAMPOLAR JET STREAM Separate polar easterlies Separate polar easterlies from prevailing westerlies from prevailing westerlies

Move East to West Move East to West Latitudes 40 N- 60 N & Latitudes 40 N- 60 N &

40 S-60 S40 S-60 S

MinorMinor

Subtropical Subtropical Separate trade winds from Separate trade winds from

westerlies westerlies Latitudes 20 N – 30 N & Latitudes 20 N – 30 N &

20 S – 30 S20 S – 30 S

GLOBAL WIND SYSTEMSGLOBAL WIND SYSTEMS Result of Earth’s rotation & uneven Result of Earth’s rotation & uneven

heating of surfaceheating of surface

Transports colder air to the Equator & Transports colder air to the Equator & warmer air to the Poles warmer air to the Poles

Help to equalize the thermal energy on Help to equalize the thermal energy on EarthEarth

Forces Influencing Wind Forces Influencing Wind Speed & DirectionSpeed & Direction

Gravitational Force:Gravitational Force: equal compression equal compression density decrease with altitudedensity decrease with altitude

Friction ForceFriction Force:: Earth’s rough surface Earth’s rough surface adds to Pressure & Coriolisadds to Pressure & Coriolis

Coriolis Force:Coriolis Force: Earth’s rotation Earth’s rotation deflecting winddeflecting wind

Pressure Gradient Force:Pressure Gradient Force: High/Low High/Low systemssystems

Why are the winds systems Why are the winds systems broken into zones??broken into zones??

Coriolis effectCoriolis effect

Coriolis EffectCoriolis Effect

Earth’s rotation Earth’s rotation breaks air masses breaks air masses into smaller cellsinto smaller cells

Moving air curves Moving air curves to the to the rightright in the in the N. Hemisphere & N. Hemisphere & to the to the left left in the S. in the S. HemisphereHemisphere

PRESSURE SYSTEMSPRESSURE SYSTEMS Low Pressure systemLow Pressure system air coming air coming

up either cloud cover / up either cloud cover / precipitation or no clouds because precipitation or no clouds because no moistureno moisture

High pressure systemHigh pressure system air coming air coming down generally fair skiesdown generally fair skies

Pressure DifferencesPressure Differences

970 mb.950 mb.

930 mb.

960 mb.

H L

Wind & Pressure RelationshipWind & Pressure Relationship

WINDSWINDS ALWAYS ALWAYS MOVE FROM MOVE FROM HIGH HIGH PRESSURE AREAS TO PRESSURE AREAS TO LOW LOW PRESSURE AREAS!!!!!!!PRESSURE AREAS!!!!!!!

Pressure CentersPressure CentersCyclones:Cyclones: centers of centers of low pressure, low pressure, Storm & CloudsStorm & Clouds (L) the pressure (L) the pressure

decreases from decreases from the outer the outer isobars toward isobars toward the centerthe center

Anticyclones: Anticyclones: centers of high centers of high pressure,pressure,

Calm & ClearCalm & Clear (H) the pressure (H) the pressure

increases from increases from the outside the outside toward the toward the centercenter

CyclonicCyclonic & & AnticyclonicAnticyclonic WindsWinds

AnticyclonesAnticyclones Winds in a high pressure area Winds in a high pressure area

move clockwise (S Hemisphere)move clockwise (S Hemisphere)

CyclonesCyclones Winds in a lower pressure area Winds in a lower pressure area

move counter-clockwise (N move counter-clockwise (N Hemisphere)Hemisphere)

CYCLONECYCLONE

ANTICYCLONEANTICYCLONE

Pressure Centers & Pressure Centers & WindsWinds

Weather and Air PressureWeather and Air Pressure Rising air is associated with cloud Rising air is associated with cloud

formation and precipitation, whereas formation and precipitation, whereas sinking air produces clear skies.sinking air produces clear skies.

Weather ForecastingWeather Forecasting Weather reports emphasize the Weather reports emphasize the

locations and possible paths of locations and possible paths of cyclones and anticyclones.cyclones and anticyclones.

Low-pressure centers can produce Low-pressure centers can produce bad weather in any season.bad weather in any season.

Pressure Systems Pressure Systems CollisionsCollisions

Collision forms a Collision forms a frontfront, , boundary that separates air boundary that separates air masses of different densitiesmasses of different densities

Air masses retain their Air masses retain their identities identities

Warmer, less dense air forced Warmer, less dense air forced aloft aloft

Cooler, denser air acts as Cooler, denser air acts as wedgewedge

4 Types of Fronts4 Types of Fronts

Warm frontWarm frontWarm air replaces cooler airWarm air replaces cooler air

•Clouds become lower as Clouds become lower as the front nearsthe front nears

•Slow rate of advance Slow rate of advance •Light-to-moderate Light-to-moderate precipitationprecipitation

Warm frontWarm front

Cold FrontsCold Fronts Cold air replaces warm airCold air replaces warm air

• Advances faster than a warm Advances faster than a warm frontfront

• Associated weather is more Associated weather is more violent than a warm front violent than a warm front •Intensity of precipitation is Intensity of precipitation is greatergreater

•Duration of precipitation is Duration of precipitation is shortershorter

Cold frontCold front

Stationary frontStationary frontFlow of air on both sides of the front is Flow of air on both sides of the front is

almost parallel to the line of the frontalmost parallel to the line of the front• Surface position of the front does Surface position of the front does not movenot move

Occluded frontOccluded frontActive cold front overtakes a warm Active cold front overtakes a warm frontfront• Precipitation is associated with Precipitation is associated with warm air being forced upwarm air being forced up

FormatioFormation of an n of an

OccludeOccluded frontd front