Meteorology 12.1 – The Causes of Weather Chapter 12 Meteorology 12.1 – The Causes of Weather

Types of atmospheric “meteors” Meteor – ancient Greek – meaning “high in the air” Clouds Raindrops Snowflakes Fog Dust Rainbows

Various phenomena Hydrometeors –primary types are cloud droplets and forms of precipitation Lithometeor – smoke, haze, dust, or condensation nuclei Electrometeors – thunder and lightning

CONTRAST Weather and 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

Compare major masses impacting North America TYPE of Air Mass Source 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

Section 12.2 Weather Systems Meteorology Section 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

3 basic zones/wind systems in each hemisphere Global Wind Systems 3 basic zones/wind systems in each hemisphere Trade winds – occur near 300 north & south latitude Air sinks, warms, and moves towards the equator Moves in a westerly direction (east to west) Prevailing Westerlies – occur between 30° and 60° north and south latitude Circulation pattern, opposite that of the trade winds Moves towards the poles Moves in an easterly direction ( west to east) Polar Easterlies – Occur between 60° latitude and the poles Similar to trade winds

Jet Streams Jet Streams affect the movement of air masses. Resemble jets of water Narrow bands of fast, high-altitude, westerly winds speed 185 km/hr

Types of fronts Types 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

-Winds move counter clockwise Pressure Systems Low pressure High Pressure - -Rising air -Winds move counter clockwise -Stormy weather - Sinking air - Winds move clockwise - Fair weather Air moves in circular motion

Gathering Weather Data Show video http://app.discoveryeducation.com/player/view/assetGuid/25B0B2A7-D01A-43D3-90BC-BC94FC1258F3

Section 12.3 Gathering Weather Data Chapter 12 Meteorology Section 12.3 Gathering Weather Data

Meteorologist (weather man) Measure atmospheric variables to make accurate weather forecasts. temperature, air pressure, wind, and relative humidity

Surface Weather Data Instruments 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