Weather Patterns

The atmosphere’s air pressure changes

Weather: condition of Earth’s atmosphere at a particular time and place. Wind is an important part of weather

Wind: air that moves horizontally or parallel to the ground, moves from a higher pressure toward lower pressure

Warmer air rises Cooler air sinks

Low Pressure High Pressure

Barometer – instrument used to measure atmospheric pressure

Global Winds

Caused by the uneven heating between the equator and the North and South poles

Travel thousands of Km in steady patterns

Last for weeks

The sinking dense air produces high pressure that sets global winds in motion

Forms because Earth’s surface is heated unevenly

The atmosphere has wind patterns

Coriolis Effect

Influenced by Earth’s rotation

Noticeable only for winds that travel long distances

Northern Hemisphere winds curve to the right

Southern Hemisphere winds curve to the left

Calm RegionsAir stays calm in HP and LP zones

Winds are light and often change direction

DOLDRUMS HORSE LATITUDES

LP zones near the equator

HP zones located about 300 N and 300 S of the equator

Warm air rises to top of troposphere Warm air traveling away

from the equator cools and sinksRising, moist air produces

clouds and heavy rain Weather tends to be clear & dry

WIND BELTS

TRADE WINDS WESTERLIES EASTERLIES

Blow from the East Blow from the

westBlow from the east

Strong & steady winds

Die out as they come near the equator

Bring storms across the U.S.

Stormy weather

JET STREAMS

Air moves at speeds > 200 km/hr

West to East

Helps make accurate weather predictions

Flow in the upper troposphere

Forms because Earth’s surface is heated unevenly

Loop N and S

LOCAL WINDS

Mountain Breezes

Valley Breezes

Land Breezes

Sea Breezes

LAND BREEZE

SEA BREEZE

Monsoons

During summer land becomes much warmer than the sea

Winds that change direction with the season

Caused by different heating and cooling rates of land and sea

Flow longer distances

During winter land becomes much cooler than the sea

Affects large areas

Most clouds form as air rises and cools

CLOUDS

Takes the form of water droplets (liquid), water vapor (gas), snow (solid)

Condensation: gas changes to a liquid

Evaporation: liquid changes into a gas (* need of extra energy)

Water always in the atmosphere

Water Stored

Lakes

Plants

Underground

Ice sheets or glaciers

Rivers

Water in the air

Frost: cold temperatures changes water vapor into a covering of ice

Precipitation: any type of liquid or solid water that falls to Earth’s surface

Dew: water that condenses on cool surfaces at night

Humidity

Humidity: the amount of water vapor in the air

Saturation: rate of evaporation and condensation are equal

Temperature effects saturation

Varies from place to place

Relative Humidity

Amount of water vapor in air

50% R. humidity ½ of the water before air is saturated

Dew Point

The amount of water to saturate the airDew point

of air the more water vapor it contains

How do clouds form

Warm air rises

Cools

Reaches dew point

Water vapor condenses

Forms droplets or crystals

Location affects the composition of clouds

3 MAIN TYPES OF CLOUDS

1.Cumulus – heap or piles, produces brief showers, puffy white, dark bases, cumulonimbus produce thunder storms, can grow very tall

2.Stratus – flat layers, dark, produce steady showers, produce circles of light around the sun or moon

3.Cirrus – feathery wisps, sign of storms, made of ice crystals, forms in cold air at high altitude, has strong windsFog – clouds that rest on the ground or a body

of water usually forms when a surface is cooler than the air above it

Water falls to Earth’s surface as precipitation.

Precipitation Forms

Crystals become heavy then fall

Growing of ice crystals

Combining of cloud droplets

Measure Precipitation

Rain Gauge

Measure snow with a ruler

Doppler radar shows images of storm systems

Types of Precipitation

Snow – ice crystals grow and merge in clouds form snowflakes, flakes come in many different shapes, when they fall through moist air near freezing form clumps, dry colder air don’t clump and snow is powdery

Hail – forms when ice pellets move up and down in clouds growing larger as they gain layers of ice, comes during warmer weather, fall from cumulonimbus clouds during thunderstorms, can vary in size to dime size to softball size

Sleet – freezes before it hits the ground, small pellets of ice, rain passes through cold air

Types of Precipitation (cont.)

Rain & Drizzle – comes from Stratus clouds, most common type of precipitation, forms from cloud droplets, light rain = drizzle

Freezing rain – can bring down trees & power lines, covers surfaces with ice