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Chapter 18
The Atmosphere
Earth’s Atmosphere
• Made of a mixture of lots of gases
21%
79%
• Pressure
– Decrease
as you go
up
• Density
– Decrease
as you go
up
Layers of the Atmosphere
• Troposphere
– Layer closest to surface (0 to 10 miles)
• 50% of all gases found below 3.5 miles
– Most dense layer of air
– Where weather occurs
– Gets cooler as you go up
• Temperature inversion can happen
– Cooler air gets trapped under hot air
– Traps the pollutants causing smog
Layers of the Atmosphere
• Stratosphere
– Second layer of the atmosphere (10 to 30 miles)
• 99% of all gases below 19 miles
– Ozone is located here
• Shields life from the dangerous UV rays
– Absorbs the UV rays given off by the sun
– Makes this layer warm
– Temperature increases as you go up
Layers of the Atmosphere
• Mesosphere
– Third layer of the atmosphere
– Layer with the coldest temperatures
• Thermosphere
– Last layer of the atmosphere
– Very hot temperatures
– Gases very spread apart
• Some escape into space
Earth’s Atmosphere
• Original atmosphere
– Mostly hydrogen, water vapor, ammonia,
methane, carbon monoxide, carbon
dioxide, and nitrogen
Earth’s Atmosphere
• Gases keep the Earth warm
– Carbon dioxide and water trap heat
– Known as the
greenhouse effect
• Must have it to
Earth
life
keep
suitable for
Earth’s Atmosphere
• Plant’s evolved by using water vapor
and carbon dioxide
– Used photosynthesis (oxygen-carbon
dioxide cycle)
Plants produce
oxygen
Plants use
carbon dioxide
Animals breath
oxygen
Animals exhale
carbon dioxide
Changes to the Atmosphere
• Photosynthesis
– Plants use carbon dioxide to make oxygen
– Puts more oxygen in the air
• Respiration
– Animals use oxygen to make carbon
dioxide
– Puts more carbon dioxide in the air
• Need a balance of carbon dioxide and
oxygen to keep the atmosphere the way
it is
Changes in the Atmosphere
• Human changes
– Appliances add chlorofluorocarbons (CFC)
• CFC destroy ozone
– Cut down trees and other plants
– Burning fossil fuels
• Drive cars, heat buildings, manufacturing
Water Cycle and Atmosphere
Water Cycle and Atmosphere
• Water evaporates from the surface into
the atmosphere
– Warmer temperature = more evaporation =
more water vapor in atmosphere
– Humidity
• Amount of water vapor in the atmosphere
Water Cycle and Atmosphere
• Dew Point
– Temperature where water vapor
condenses
– Depends on humidity
• Higher humidity leads to higher dew point
Water Cycle and Atmosphere
• Water vapor condenses in air
– Forms tiny drops of liquid water and ice
• Known as Clouds
• Clouds get very full and very heavy
– Water will begin to fall because of the
weight and gravity
• Known as precipitation
– Rain, snow, hail, sleet
Cirrus Clouds
Types of Clouds
Cumulus Clouds
Fog - Very Low Clouds
Stratus Clouds
Pressure and Atmosphere
• Air pressure is read with a barometer
– Weight of all atmosphere pushing down
– Cool air has higher pressure
– Drops in pressure indicate stormy weather
• High pressure = fair weather
• Low pressure = clouds and precipitation
Pressure and Atmosphere
• Difference in air pressure creates wind
– Air moves from high pressure to low
pressure
• Larger difference = stronger winds
– Areas of equal pressure are connected by
isobars on a weather map
• Close bars = strong winds
Coriolis Effect
Close isobars = high winds
Fronts and Weather
• Air Masses
– Body of air with the same temperature and
humidity
• Front
– Boundary between different air masses
– Three main types
• Cold
• Warm
• Stationary
Fronts and Weather
• Warm Front
– Warm air mass moves toward and over
cold air mass
– Clouds usually form
• Start as high cirrus clouds
• Later form heavy stratus clouds that release
precipitation for a few days
Weather Map
Symbol
Fronts and Weather
• Cold Front
– Cold air mass moves under a warm air
mass
– Very steep edge so cumulus clouds form
quickly and are very heavy
– High winds, thunderstorms, tornadoes
occur here
Weather Map
Symbol
Fronts and Weather
• Stationary Front
– Two different air masses sit along side
each other
– Act similar to a warm front
– Weather usually stays the same for a few
days
Weather Map
Symbol
Fronts and Weather
• Thunderstorms
– Precipitation storms with lightning and
thunder
• Lightning = sparks that jump between clouds
and ground because of a difference in electric
charge
• Thunder = sound of lightning moving through
the air
Fronts and Weather
• Tornadoes
– High speed, rotating winds that extend out
of thunderclouds
– Most common in Midwest region of the US
from April until June
– Watches are set when conditions are right
– Warnings are set when one has been
spotted
Fronts and Weather
• Hurricanes
– Similar to tornadoes, but they form over
water
• Water powers the hurricane so the longer it is
over water, the worse it can be
– Usually occur in late summer to early fall
– Also called cyclones and typhoons in other
parts of the world
Weather and Climate
• Climate
– The average weather patterns of a certain
area over many, many years
– Depends on location on Earth and surface
features in the area
Weather and Climate
• Temperatures are hotter closer to the
equator because of more direct sunlight
Weather and Climate
• Seasons occur because Earth tilts and it
moves around the sun
Weather and Climate
• Surface features of Earth
– Mountains cause air to rise, cooling it,
forming clouds
– Oceans currents cause air to cool down
– Bodies of water cause air to be more
humid
– Flat lands don’t stop air from flowing so lots
of winds