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Chapter 4
Global Climates and Biomes
Describe the Case Study:
Floods, Droughts, and Famines of
Western and Northeastern Kenya
Global Processes Determine Weather
and Climate
• Weather- the short term conditions of the atmosphere
in a local area.
• - These include temperature, humidity, clouds,
precipitation, wind speed and atmospheric pressure.
• Climate- The average weather that occurs in a given
region over a long period- typically several decades.
• Regional differences in temp. and precipitation help
determine which organisms can survive in each
region.
Earth's Atmosphere
• Atmosphere consists of
5 layers of gases.
• - What keeps these gas
molecules in place?
• - Explain the
relationship between
altitude, temp and
density of gas
molecules for each
layer of the
atmosphere.
Earth's Atmosphere
1. Troposphere- the layer closest to Earth's
surface extending roughly 16 km (10 miles)
above Earth.
- Characteristics:
- Characterized by a great deal of circulation
and mixing of liquids and gases.
2. Stratosphere- above the troposphere, this
extends from roughly 16 to 50 km (10-31
miles).
- Characteristics:
- Provides critical protection for our planet.
Earth's Atmosphere
-Mesosphere -
-Thermosphere -
-Exosphere - Atmospheric pressure
and density in each of these
layers decreases as it extends
out into space.
5 Processes that affect the distribution of
heat & precipitation across the globe
• 1. Unequal heating of the Earth by the Sun
• 2. Atmospheric Convection currents
• 3. The rotation of Earth
• 4. Earth’s orbit around the Sun on a tilted axis
• 5. Ocean currents
1. Unequal Heating of Earth
• As the Sun's energy passes through the atmosphere and
strikes land and water, it warms the surface of Earth.
• But this warming does not occur evenly across the
planet.
• Uneven heating drives the circulation of air.
• 3 factors that cause the unequal heating:
1.
2.
3.
1. Unequal Heating of Earth
• This unequal heating is because:
1.
The variation in angle at which the Sun's rays strike Earth.
- Equator =
- Mid-latitude and
polar regions
=
- Higher latitudes mean sunlight passes through more atmosphere
therefore less solar energy reaches there than the equator.
1. Unequal Heating of Earth
• This unequal heating is because:
2. The variation in the amount of surface area over
which the Sun's rays are distributed.
- Equator =
- Mid-latitude and
polar regions
=
1. Unequal Heating of Earth
• This unequal heating is because:
3. Some areas of Earth reflect more solar energy than
others. (Albedo = the % reflected from the surface)
The higher the
albedo of a
surface, the more
solar energy it
reflects, and the
less it absorbs.
2. Atmospheric Convection Currents
are driven by uneven heating
Air has four properties that determines its
movement:
• 1. Density- less dense air rises, denser
air sinks.
• 2. Water vapor capacity- warm air has a
higher capacity for water vapor than
cold air.
• - Hot summer days associated with
high humidity.
• - Saturation point =
• - Correlation to the water cycle?
2. Atmospheric Convection Currents
• Air has four properties that
determines its movement:
• 3. Adiabatic cooling- as air
rises in the atmosphere its
pressure decreases and the air
expands in volume. This
expansion lowers the temp. of
the air.
• Adiabatic heating - Conversely,
as air sinks, the pressure
increases and the air decreases
in volume. This decrease in
volume raises the temp.
3. Atmospheric Convection Currents
Air has four properties that determines its movement:
• 4. Latent heat release- when vapor in the atmosphere
condenses into water, energy is produced.
• - Whenever water vapor in the atmosphere condenses, the
air will become warmer, and this warm air will rise.
Formation of Convection Currents
• Atmospheric convection currents are global patterns of air
movement that are initiated by the unequal heating of Earth.
• Convection currents form a river of air flow.
• Trace the flow of heat from the sun starting at the tropics:
Formation of Convection Currents—
Hadley Cell
Formation of Convection Currents
• Atmospheric convection currents are global patterns of air
movement that are initiated by the unequal heating of Earth.
• Hadley cells- the convection currents that cycle between the
equator and 30˚ north and south.
• Intertropical convergence zone = the equator - the area of
Earth that receives the most intense sunlight and where the
ascending branches of the two Hadley cells converge. (ITCZ)
• Polar cells- the convection currents that are formed by air
that rises at 60˚ north and south and sinks at the poles (90˚
north and south)
3. Earth's Rotation and the Coriolis Effect
• As Earth rotates, its surface
moves much faster at the
equator than in mid-latitude
and polar regions due to the
equators larger diameter.
• The faster rotation speeds
closer to the equator cause a
deflection of objects that are
moving directly north or south
known as the Coriolis Effect.
3. Earth's Rotation and the Coriolis Effect
Earth's Rotation and the Coriolis Effect
• Coriolis Effect- the deflection of an object's path due
to Earth's rotation.
• The prevailing winds of the world are produced by a
combination of atmospheric convection currents and
the Coriolis effect.
• If the Earth did not rotate, the air within each
convection cell would simply move directly north or
south and cycle back again.
•
•
•
•
•
Because of the Coriolis effect, the
Hadley cell north of the equator
produces prevailing winds along
Earth’s surface that come from
the northeast (northeast trade
winds)
The same is true for the opposite
(southeast trade winds)
Westerlies – Earth is rotating
faster at 30o than at 60o, air
movement is deflected because
of the faster speed to the east.
The combined air currents and
the Coriolis effect cause regions
north of 300 to experience
prevailing winds from the
southwest.
The same is true for the
northwest.
Summary
Atmospheric convection currents of
tropical (Hadley cells) and polar
latitudes (Polar cells) + mixing of
air currents in the mid-latitudes
(NE and SE trade winds and the
westerlies) + the Coriolis effect
(deflection) cause prevailing
wind patterns.
4. Earth's Tilt and the Seasons
• The Earth's axis of rotation is tilted 23.5 ˚.
• Earth’s orbit around the sun causes most regions of the world to
experience seasonal changes in temp. and precipitation.
• When the Northern Hemisphere is tilted toward the Sun, the
Southern Hemisphere is tilted away from the Sun, and vice
versa.
• March equinox and September equinox –
• Sun directly above the Tropic of Cancer 23.5 ˚N (June solstice) –
• Sun directly above the Tropic of Capricorn 23.5 ˚S – (Dec
solstice) -
5. Ocean Currents
• Ocean currents are driven by a combination of temperature,
gravity, prevailing winds, the Coriolis effect, and the
locations of continents.
• Warm water, like warm air, expands and rises.
• What does this higher elevation at the tropics cause?
• Gyres- the large-scale patterns of water circulation. The
ocean surface currents rotate in a clockwise direction in the
Northern Hemisphere and a counterclockwise direction in
the Southern Hemisphere.
• Explain the movement for each hemisphere.
Oceanic Circulation Patterns
Ocean Currents and Upwelling
• Upwelling- as the surface currents separate from
one another, deeper waters rise and replace the
water that has moved away.
• This upward movement of water brings nutrients
from the ocean bottom that supports the large
populations of producers, which in turn support
large populations of fish = highly productive
ecosystem.
Thermohaline Circulation
• Thermohaline circulation- drives the mixing of surface water and
deep water.
• Why is this crucial?
• It appears to be driven by surface waters that contain unusually large
amounts of salt.
• Some of the warm water that flows from the Gulf of Mexico to the
North Atlantic freezes or evaporates, and the salt that remains
behind increases the salt concentration of the water.
• This cold, salty water is relatively dense, so it sinks to the bottom of
the ocean, mixing with deeper ocean waters.
• These two processes create the movement necessary to drive a deep,
cold current that slowly moves past Antarctica and northward to the
northern Pacific Ocean.
Heat Transport
• Ocean currents can affect the temperature of nearby
landmasses.
• How does heat transport relate to the present concern about
global warming?
El Nino-Southern Oscillation (ENSO)
• Every 3 to 7
years, the
interaction of
the Earth's
atmosphere
and ocean
currents cause
surface
currents in the
tropical
Pacific Ocean
to reverse
direction.
El Nino-Southern Oscillation
• 1. First, the trade winds (SE) near South America weaken.
• 2. This weakening allows warm equatorial water from the
western Pacific to move eastward toward the west coast of
South America.
• 3. The movement of warm water and air toward South
America suppresses upwelling off the coast of Peru and
decreases productivity there, reducing fish populations near
the coast.
• 4. These periodic changes in wind and ocean currents are
collectively called the EL Nino-Southern Oscillation, or
ENSO.
• Global Impact?
Rain Shadows
Air moving inland from the ocean that contains a large amount of water
vapor meets the windward side of a mountain range (the side facing the
wind), it rises and begins to experience adiabatic cooling.
Because water vapor condenses as air cools, clouds form on the windward
side of the mountain range and precipitation falls.
The cold, dry air from the latent heat release then travels to the other side
of the mountain range (the leeward side), where it descends and
experiences higher pressures, which cause adiabatic heating.
This now warm/dry air produces arid conditions on the leeward side
forming the region called a rain shadow.
Variations in Climate Determine the Dominant
Plant Growth Forms of Terrestrial Biomes
• Climate affects the distribution of species around the globe.
• Organisms possess distinct growth forms due to adaptations
to local temperature and precipitation patterns.
What type of evolution is this?
Variations in Climate Determine the Dominant
Plant Growth Forms of Terrestrial Biomes
Biomes- The presence of similar plant growth forms in
areas possessing similar temperature and precipitation
patterns.
Climate Diagram
Biomes can suggest where we use the land and how we can use it.
Growing crops = high temps, longer season, high rain
Grazing and grass crops = warm but less rain
Lumber = cold forests