Chapter 4Global 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.

• 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

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.

SummaryAtmospheric 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 BiomesBiomes- 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