Transcript Chapter 4 - Liberty Union High School District

Chapter 4
GLOBAL CLIMATES AND BIOMES
Atmosphere
 Weather is short term conditions of atmosphere
 Climate is long term conditions
 5 major processes influence climate/weather: unequal heating of
earth, convection currents, Coriolis effect, tilt, and oceans
 Atmosphere has 4-layers:
1. Troposphere (0-20km): bottom layer, densest, where most weather
and mixing occurs, temps get colder with height
2. Stratosphere (20-50km): second layer, gets warmer with height,
contains ozone layer that absorbs UV light
3. Mesosphere (50-80km) – third layer, coldest, meteorites burn up
4. Thermosphere – top layer, warmest, absorb gamma rays
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Atmosphere protects organisms from radiation and it regulates
temperatures
Past Climate Study
 Trapped bubbles in ice cores provide a timescale of:
Atmospheric composition, greenhouse gas concentrations,
temperature trends
 Snowfall, solar activity, and frequency of fires
 Ice cores go back 800,000 years
 Cores in sediment beds preserve pollen grains and other plant
remnants
 Tree rings indicate age, precipitation, droughts, and fire history
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 http://www.ted.com/talks/lang/en/al_gore_warns_on
_latest_climate_trends.html
1. Unequal Heating
 Atmosphere is heated unevenly for 2 reasons
Tilt of the earth
2. Some areas on earth reflect more sunlight than other
areas (albedo)
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White surface has higher albedo than black surface
This uneven heating of the atmosphere drives
convection currents in the atmosphere
2. Atmospheric Convection Currents
 Air has 4 properties that determine how it will circulate
Density: less dense air rises (warm), more dense air
sinks (cold)
2. Water vapor capacity: warm air can hold more water
vapor (saturation point) which is less dense
3. Adiabatic heating/cooling:
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When air rises, pressure decreases and air expands and temps
lower due to less friction between air molecules
When air sinks, pressure increases and air compresses and
temps rise due to more friction between air molecules
4. Latent heat release: when air condenses, the energy
that evaporated it is released and air warms
(2). Formation of Convection Currents
 Air rises in warm, moist tropics
 Rising air experiences lower atmospheric pressure and
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adiabatic cooling until it reaches saturation point
This leads to condensation which releases latent heat
Eventually air cools and spreads out and begins to sink
around 30⁰ latitude (deserts)
When sinking air hits the ground, it spreads in all
directions completing the cycle, called a Hadley cell
Air re-converges at the equator, called the intertropical
convergence zone (ITCZ)
Polar regions cause additional Hadley cells
3. Earth’s Rotation and Coriolis Effect
 Earth rotates faster at equator than poles
 Objects’ paths get deflected due to the rotation of earth.
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This is known as the Coriolis effect
This deflects winds and sets up weather patterns
Trade winds blow towards the equator between 0- 30°.
They meet at the equator and rise creating calm winds
called the doldrums
Where the air sinks at 30° is the horse latitudes
Air moves north from here, Coriolis force deflects it to
right, and get westerlies (40°-60°)
At poles, the air sinks and moves towards the equator,
but gets deflected to right. This creates polar easterlies
4. Earth’s Tilt and Seasons
 Earth is tilted 23.5⁰
 When northern hemisphere is pointed towards the sun they
experience summer
 When northern hemisphere is pointed away from the sun
they experience winter (southern hemisphere is opposite)
 Vernal/automnal equinoxes, everywhere receives 12h
daylight
 Poles have 6 months of darkness and 6 months of daylight
5. Ocean Currents
 Currents driven by temp, gravity, prevailing winds, Coriolis
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effect, and continents
Water is warmer at the equator, so it expands and rises. This
makes the water higher then the rest of earth and gravity takes
over
Winds and Coriolis effect start ocean currents and deflect
them. Called gyres (transport heat)
Upwelling (rising of water) occurs along coastlines
Thermohaline circulation is when water is saltier, making it
more dense, so it sinks
ENSO (El Nino – Southern Oscillation– when ocean currents
change direction, thus affecting climates (La Nina)
Rain Shadows
 Air rises on one side of a mountain range and moisture
condenses out
 On other side, air sinks preventing clouds and it
remains dry
 Dry region is called a rain shadow
Altitudes create “latitudinal” patterns
 Vegetative communities rapidly change along
mountain slopes
 The climate varies with altitude
 A mountain climber in the Andes
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Begins in the tropics and ends
on a glacier
 Rainshadow effect = air going
over a mountain releases
moisture
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Creating an arid region
on the other side
Biomes
 Biomes are large regions characterized by a specific
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type of climate and certain types of plant and animal
communities
Largest category scientists use to classify ecosystems
Each biome has many ecosystems
Biomes described by vegetation because that
determines organisms and amount of vegetation is
determined by climate
At altitude and latitude increase, temps decrease