WEATHER2.ppt

• _{Radiant energy – energy from the sun}

• _{Radiant energy is absorbed by Earth and}

3 Methods of Heat Transfer

1. Conduction

• direct transfer of heat from one thing to another

• warm ground causes the air around it to heat up

2. Convection

• transfer of heat energy in liquids and gases

• convection currents transfer most of the energy in the atmosphere

3. Radiation

• transfer of energy by waves

Greenhouse Effect

• _{energy from the sun is turned into infrared}

radiation

• gases like carbon dioxide (CO₂) trap IR

radiation

Why do temperatures vary

around the world?

• Angle simulation

• _{sun strikes Earth at different angles}

• _{greatest heating occurs when sun’s rays hit}

Earth straight on

• _{farther away from the equator = less radiant}

Atmospheric Pressure

• _{force of air pressing on Earth’s surface}

• _{depends on density of air}

• _{Density – amount of mass in a certain}

Factors Affecting Air Pressure

1. Temperature

• density affected by temperature • high temps = lower air pressure

2. Water Vapor

• moist air is less dense than dry air • drier air = higher pressure

3. Elevation

• higher altitude = thinner air

Forecasting Weather Using a

Barometer

• _{Barometer: measures air pressure}

• _{High pressure = Good weather}

Winds

• _{Winds are formed by movement of air from}

one place to another

• _{2 Types: local and global}

• _{Both caused by differences in air pressure}

Local Winds

• _{Convection Currents}

• _{sea breeze – flow of air from sea to land} • _{land breeze – flow of air from land to sea}

• _{name tells from which direction wind is blowing} • _monsoon

• _{major land and sea breeze} • _{seasonal wind}

Global Winds

• _{caused by unequal heating of Earth}

• _{curve right in northern hemisphere}

• _{Coriolis effect – winds shift because Earth}

• _Doldrums

• _{at equator, winds are weak or do not form at all} • _{cooler northern air is heated rapidly in this area}

• _{Trade Winds}

• 30 north and south of equator

• _{belt of warm, steady winds}

• _{Prevailing Westerlies}

• winds appear to travel from west to east

• _{Polar Easterlies}

• winds appear to travel east to west

• cold, weak winds

• affect weather in the U.S.

• _{Jet Streams}

• narrow belt of strong, high-speed, high-pressure air

• flow west to east

• much faster in winter

• do not circle Earth in regular pattern

Measuring Weather

• _{wind vane – measures direction}

• _{anemometer – measures speed}

• _{Barometer: measures air pressure}

• _{psychrometer – used to measure relative}

Moisture in the Air

• evaporation – H₂O molecules escape into

air

• _{humidity – water vapor (moisture) in the}

air

• _{relative humidity – percentage of}

• _{psychrometer – used to measure relative}

humidity

• _{2 thermometers}

• _{wet bulb – evaporation cools thermometer} • _{dry bulb – measures air temperature}

Clouds

• _{dew point – temp at which water vapor}

condenses

• _{Clouds form when moisture in air}

3 Main Types of Clouds

1. Cumulus

• “cotton balls” in the sky

• fluffy with flat bottoms

• form at 2.4 to 13.5 km

• usually mean fair weather

• can form thunderstorms

2. Stratus Clouds

• smooth, gray clouds

• cover entire sky, block out sun

• form at 2.5 km

• bring light rain and drizzle

• can form close to ground - fog

3. Cirrus Clouds

• _{feathery clouds}

• _{form between 6 and 12 km} • made of ice crystals

Precipitation

• _{water vapor that condenses, forms clouds, and}

falls to Earth as rain, sleet, snow, or hail

• _{cloud drops get larger by bumping into one}

another

• _{gravity pulls large drops to Earth as rain} • _{rain can freeze on the way down}

• _{rain can freeze immediately and form snow}

• _{six-sided intricate crystals}

• _{hail forms in cumulonimbus clouds}

• _{water droplets hit ice pellets and freeze,}

air masses

• _{air masses – large bodies of air with same}

temperature and humidity

• _{tropical masses – warm}

• _{polar masses – cold}

• _{continental – dry}

4 major classes

1. maritime tropical

2. maritime polar

3. continental tropical

4. continental polar

• _{front – boundary between two air masses} • _{4 major types}

1. cold front

• mass of cold air pushes under mass of warm air • _{violent storms followed by clear weather}

2. warm front

3. occluded front

• _{Warm air stuck above two cold air masses} • _{less extreme weather patterns}

4. stationary front

• _{warm air meets cold air and no movement}

occurs

Storms

• _{violent disturbance in air}

Rain and Snow Storms

• _{fronts collide}

• _{warm front meets cold front}

• _{nimbostratus clouds form}

Thunderstorms

• _{cold front meets warm front}

• _{cumulonimbus clouds form}

• _lightning

• + and – charges build up in clouds

• sudden discharge of electricity

• between 2 clouds or cloud and ground

• _thunder

• electrical discharge heats air

• air expands rapidly and causes sound waves

Hurricane

• _{powerful cyclone that forms over tropical oceans}

• _{typhoon – forms over Pacific Ocean}

• _{air pressure in center drops – more air sucked in}

• _{air spins faster and rises}

• _{wall of strong winds and clouds forms}

Tornado

• _{whirling, funnel-shaped cloud}

• _{forms in low, heavy, cumulonimbus clouds}

• _{extremely low pressure at bottom of funnel}

• _{low pressure area acts like a vacuum}

cleaner