Wind and RainWind and Rain

3/8/103/8/10

WindWind

WindWind – the horizontal movement of air – the horizontal movement of air from an area of high pressure to an area from an area of high pressure to an area of lower pressure.of lower pressure.

All winds are caused by differences in air All winds are caused by differences in air pressure.pressure.

Measuring WindMeasuring Wind

AnemometerAnemometer – has 3 or 4 cups mounted at – has 3 or 4 cups mounted at the ends of spokes that spin on an axle. the ends of spokes that spin on an axle. The force of the wind spins the cups and a The force of the wind spins the cups and a speedometer is connected to the cups to speedometer is connected to the cups to measure the wind speed. measure the wind speed.

Wind-Chill FactorWind-Chill Factor

Wind blowing over your body cools your Wind blowing over your body cools your skin. The stronger the wind the cooler you skin. The stronger the wind the cooler you feel.feel.

Wind-Chill FactorWind-Chill Factor – the increased cooling – the increased cooling that a wind can cause. that a wind can cause.

Local WindsLocal Winds

Local windsLocal winds – wind that blows over a short – wind that blows over a short distance that are caused by unequal distance that are caused by unequal heating of the Earth’s surface within that heating of the Earth’s surface within that small area. small area.

Global WindsGlobal Winds

Global WindsGlobal Winds – winds that blow steadily – winds that blow steadily from specific directions over long from specific directions over long distances. distances.

Coriolis EffectCoriolis Effect

Coriolis EffectCoriolis Effect – the way the Earth’s – the way the Earth’s rotation makes winds curve. rotation makes winds curve. Coriolis was a French mathematician who Coriolis was a French mathematician who

studied and explained it in 1835. studied and explained it in 1835.

Horse LatitudesHorse Latitudes

Horse LatitudesHorse Latitudes – at 30 – at 30oo and 60 and 60oo the winds the winds do not go up or down. do not go up or down.

Wind BeltsWind Belts

The major global wind belts are:The major global wind belts are: Trade windsTrade winds Prevailing WesterliesPrevailing Westerlies Polar EasterliesPolar Easterlies

Trade WindsTrade Winds

Trade windsTrade winds – winds that blow from the – winds that blow from the horse latitudes towards the equator.horse latitudes towards the equator.

Prevailing WesterliesPrevailing Westerlies

WesterliesWesterlies – winds that blow away form – winds that blow away form the horse latitudes. These winds blow the horse latitudes. These winds blow southwest between 30southwest between 30oo and 60 and 60oo north. north.

Polar EasterliesPolar Easterlies

Polar EasterliesPolar Easterlies – cold air near the poles – cold air near the poles sinks and flows back down. The Coriolis sinks and flows back down. The Coriolis effect shifts these winds to the west effect shifts these winds to the west meeting at the 60meeting at the 6000

CloudsClouds

Meteorologists have put clouds into three Meteorologists have put clouds into three main groups:main groups: CumulusCumulus StratusStratus Cirrus Cirrus

CumulusCumulus

CumulusCumulus – heap or mass. These clouds are – heap or mass. These clouds are fluffy and look like cotton candy. fluffy and look like cotton candy.

They are anywhere from 2-18 km off the They are anywhere from 2-18 km off the ground. ground.

A sign of good or fair weather. A sign of good or fair weather.

StratusStratus

StratusStratus – spread out. These clouds have – spread out. These clouds have flat layers and cover most of the sky. flat layers and cover most of the sky.

As they get thick they can produce rain or As they get thick they can produce rain or snow. snow.

CirrusCirrus

CirrusCirrus – high feathery clouds that are – high feathery clouds that are made of ice crystals above 6 km. made of ice crystals above 6 km.

NimbusNimbus – rain – rain

(cumulonimbus is a storm cloud)(cumulonimbus is a storm cloud)

Alto – Alto – highhigh

(altostratus is a high, flat cloud)(altostratus is a high, flat cloud)

Cloud layersCloud layers

The layers of clouds starting from the ground are:The layers of clouds starting from the ground are:

FogFog CumulusCumulus StratusStratus NimbostratusNimbostratus CumulonimbusCumulonimbus AltostratusAltostratus AltocumulusAltocumulus CirrocumulusCirrocumulus CirrusCirrus

The Water CycleThe Water Cycle

EvaporationEvaporation – liquid water escapes into the – liquid water escapes into the air as water vapor.air as water vapor.

The water cycle is the movement of water The water cycle is the movement of water between the atmosphere and the Earth. between the atmosphere and the Earth.

HumidityHumidity

HumidityHumidity – a measure of the amount of – a measure of the amount of water vapor in the air.water vapor in the air.

Humidity can be measured using a Humidity can be measured using a psychrometer. psychrometer.

How Clouds FormHow Clouds Form

Clouds form when water vapor in the air Clouds form when water vapor in the air becomes liquid water or ice crystals which becomes liquid water or ice crystals which is called is called condensation.condensation.

How Clouds FormHow Clouds Form

Dew PointDew Point – the temperature at which – the temperature at which condensation begins. condensation begins.

PrecipitationPrecipitation – any form of water that falls – any form of water that falls from clouds and reaches Earth’s surface. from clouds and reaches Earth’s surface.

RainRain

Most common form. Water drops must be Most common form. Water drops must be at least 0.5 mm or larger in diameter in at least 0.5 mm or larger in diameter in order to be rain. order to be rain.

SleetSleet

If the temperature of the air is below 0If the temperature of the air is below 0ooC C then the rain will freeze. If it is less than 5 then the rain will freeze. If it is less than 5 mm in diameter then it is considered sleet. mm in diameter then it is considered sleet.

Freezing RainFreezing Rain

If the rain doesn’t freeze until it reaches If the rain doesn’t freeze until it reaches the ground, then it is considered freezing the ground, then it is considered freezing rain and is very dangerous. rain and is very dangerous.

HailHail

Round pellets of ice larger than 5 mm in Round pellets of ice larger than 5 mm in diameter are called hail. Hail forms in diameter are called hail. Hail forms in cumulonimbus clouds during cumulonimbus clouds during thunderstorms. thunderstorms.

SnowSnow

When water vapor changes directly into When water vapor changes directly into ice crystals. All snowflakes have exactly 6 ice crystals. All snowflakes have exactly 6 sides or branches. sides or branches.

DroughtsDroughts

Long periods of unusually low precipitation Long periods of unusually low precipitation Cloud seeding helps get rid of droughts Cloud seeding helps get rid of droughts

when silver iodine is placed into clouds with when silver iodine is placed into clouds with airplanes. airplanes.