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