Chapter 12Meteorology

12.1 – The Causes of Weather

Meteor – ancient Greek – meaning “high in the air”1. Clouds2. Raindrops3. Snowflakes4. Fog5. Dust6. Rainbows

Types of atmospheric “meteors”

Hydrometeors –primary types are cloud droplets and forms of precipitation

Lithometeor – smoke, haze, dust, or condensation nuclei

Electrometeors – thunder and lightning

Various phenomena

WEATHER CLIMATE

DESCRIPTION Current state of atmosphere Average weather

TERM, MEASURE OF VARIATIONS

Short term variations (minutes, hrs, days, weeks, months, years)

Over a long period, 30 years or more

CONTRAST Weather and Climate

TYPE of Air MassSource of Air

Mass

Weather Associated with

Air Mass

Continental Tropical (cT)

Desert Southwest & Mexico

Hot, dry summers

Maritime Tropical(mT)

Caribbean Sea Gulf of Mexico

Hot & humid summers

Continental Polar (cP)

Interior of Canada and Alaska

Very cold, frigid winter when nights are long

Maritime Polar (mP)

North Atlantic North Pacific

Heavy rains in winter on West Coast

Artic (A) Siberia & Arctic Basin

No solar radiation. Very cold/bitter cold & dry

Compare major masses impacting North America

MeteorologySection 12.2

Weather Systems

Why are most tropical rain forests located near the equator?

Equator- the trade winds from both hemispheres meet

ITCZ (Inter tropical convergence zone)

The rising air over a large area creates clouds and abundant precipitation

Global Wind Systems3 basic zones/wind systems in each hemisphere

1. Trade winds – occur near 300 north & south latitudeAir sinks, warms, and moves towards the equatorMoves in a westerly direction (east to west)

2. Prevailing Westerlies – occur between 30° and 60° north and south latitudeCirculation pattern, opposite that of the trade windsMoves towards the poles Moves in an easterly direction ( west to east)

3. Polar Easterlies –Occur between 60° latitude and the polesSimilar to trade winds

Jet StreamsJet Streams affect the movement of air masses.Resemble jets of waterNarrow bands of fast, high-altitude, westerly winds

speed 185 km/hr

Types of frontsTypes of front

Map symbol

Description of air movement

Associated weather

COLD FRONT

Forces warm air up along a steep front

Clouds, showers, some thunderstorms

WARM FRONT

Warm air displaces cold air, warm air encounters less friction w/ ground

Extensive cloudiness & precipitation

STATIONARY FRONT

Two air masses meet. Neither advances to the others territory

Similar to warm front

OCCLUDED FRONT

Moves rapidly that it overtakes a warm front

precipitation

Earth’s rotation affects air movement

Rising & sinking air, combined with Coriolis effect result in formation of low & high pressure systems.Air at Earth’s surface spreads away from the center

Pressure Systems

-

-Rising air-Winds move

counter clockwise -Stormy weather

- Sinking air- Winds move clockwise- Fair weather

Air moves

in circula

r motion

High PressureLow pressure

Gathering Weather DataShow videohttp://

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Chapter 12Meteorology

Section 12.3Gathering Weather Data

Meteorologist (weather man)Measure atmospheric variables to make accurate weather forecasts.

1. temperature, 2. air pressure, 3. wind, and 4. relative humidity

Surface Weather Data InstrumentsInstrument

What does it measure?

How does it work?

Thermometer Temperature Mercury / alcohol expand with heat

Barometer Air pressure

Changes in pressure measured by changes in height of column of mercury

Anemometer Wind speed & direction

Rotates as the wind blows

Hygrometer Relative humidity Wet and dry bulb thermometers

Ceilometer Height of cloud layers Data collected by ASOS

Radiosonde – balloon-borne pkg.

Upper –level date (temp air pressure, humidity

Radio signal back to ground station

The End