Transcript Understanding Our Environment

Air, Weather, and Climate
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Earth’s Atmosphere
Compared to the size of the Earth (12000 km),
the atmosphere is a thin shell (120 km)
Composed of:
– ~78% N2 gas
– 21% O2 gas
– 1% argon gas and other permanent gases
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If the Earth is
compared to
this Orange…
the Earth’s
atmosphere
would be
thinner than
the layer of
pesticide on
this Orange’s
surface
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Layers of the Atmosphere
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Troposphere
Stratosphere
Mesosphere
Thermosphere
Ionosphere
Exosphere
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Troposphere
 Closest to the earth’s surface
 Where we live
– Weather occurs here
 very thin (averaging 11 km or 7 miles high)
 Densest layer
– Most of nitrogen, oxygen and water vapor here
 Temp decreases as altitude increases
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Stratosphere
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Above the troposphere
extends to 50 kilometers (31 miles) high
dry and less dense
UV rays reach higher altitudes and warm them
Ozone layer
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Mesosphere
 extends to 85 kilometers (53 miles) high
 temperature decrease with altitude reaching
-90°C at the top
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Thermosphere
 extends to 600 kilometers (372 miles) high
 temperatures go up as altitude increases due to
absorption of solar radiation by oxygen
 molecules so few and far between that they
collide rarely
 Farthest away from earth’s surface
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Ionosphere
 Within the thermosphere
 Contains ions when hit by solar energy begin to
glow and produce light
– Aurora Borealis
 reflects many types of radio waves allowing
them to bounce around the world
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Exosphere
 Top of the thermosphere and continues until it
merges with interplanetary gases, or space (372
to 6200 miles)
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Seasonal Changes
 Occurs due to
earth’s axis being
tilted
 Creates opposite
seasons
 Factor that
determines global
air circulation
patterns
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Seasons
 Seasons are short periods
of climatic change.
 Certain areas receive
changing amounts of
radiation throughout the
year
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Earth’s Seasons
SUMMER (Northern Hemisphere)
WINTER (Southern Hemisphere)
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Earth’s Seasons Continued….
Tilt of the Earth’s axis towards or away from the sun creates the seasons
WINTER (Northern Hemisphere)
SUMMER (Southern Hemisphere)
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Weather
 Weather – daily temperature and moisture
conditions in a place
– driven by atmosphere
– atmospheric conditions over short time periods (hours
or days) in small geographic areas
– produced by interacting air masses
– Types of weather
 Warm Front-warm air displaces cool air
 Cold Front-cooler air displaces warmer air
 Severe-hurricanes, thunderstorms, tornadoes
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Weather
 Contribute to Weather
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Air temperature
Air pressure
Humidity
Cloud cover
Precipitation
Winds
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Air Temperature
 As solar energy reaches the equator, regions heat
up more than the poles.
 Warm air and water at the equator travel toward
the poles while cold air and water at the poles
travel toward the equator in an attempt to
equalize the temperature
– Constant struggle = changing weather
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http://www.usatoday.com/weather/tg/wglobale/wglobale.htm
Air Pressure
 Caused by the weight of air pressing down on the Earth
 High pressure-cool, dense air that descends towards
surface of earth
– Fair weather
 Low pressure-less dense warm air goes toward the
center of a low pressure air mass
– Produces cloudy and stormy weather
 Air pressure changes with weather
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Humidity and Cloud Cover
 Relative humidity-amount of water vapor in the air
 Cloud Cover
– clouds cool the planet by reflecting sunlight
 Albedo
– reduces the amount of heat that radiates into space
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Winds
 Speed is determined by differences in pressure
 Coriolis effect
– Deflection of objects moving in a straight path
relative to the earth’s surface
– Proportional to the speed of the earth’s rotation at
different latitudes
 as latitude increases and the speed of the earth’s rotation
decreases, Coriolis effect increases
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Winds cont.
 Hadley cells
– Solar energy warms humid air in tropics
– Warm air rises, cools, condenses and precipitates
– Dry air sinks and is warmed
 Hot dry air causes deserts
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Convection Currents
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Climate
 Climate – long term weather patterns
– driven by atmosphere
– determines distribution of biomes across Earth
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What Factors Control Climate?
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Latitude
Elevation/topography
Nearby water
Uneven heating of earth’s surface
Ocean currents
Vegetation
Prevailing winds
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Ocean Currents
 Warm/cold currents influence land climate
 Currents redistribute heat from sun which influences climate
– Gulf Stream current
 Upwelling-occurs along the west coasts of most continents
– Cold, nutrient filled water
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le
 Warm phase of ENSO
 El Nino – trade winds near SA weaken; allows warm equatorial water
from the western Pacific to move eastward toward the west coast of
SA
– Suppresses upwelling; decreases productivity
– Alters weather
 Cooler, wetter conditions in the se US
 Cold phase of ENSO
 La Nina
– Trade winds strengthen
– Upwelling of nutrient rich waters
– Alters weather
 Drier conditions in the se US
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“Natural” Greenhouse Effect
 Solar radiation passes through the atmosphere.
– ~51% of the sun's radiation reaches the surface
 This energy is then used in number of processes including:
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–
–
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heating of the ground surface
melting of ice and snow
evaporation of water
plant photosynthesis
– ~30% is reflected back to space by clouds and the surface
– ~19% of the energy available is absorbed by clouds and gases
 absorb and reradiate this outgoing radiation, storing some of the heat
in the atmosphere, thus producing a net warming of the surface
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“Natural” Greenhouse Effect cont.
 Kept the Earth's temperature about 60° F
warmer than it would otherwise be.
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