Global Climates and Biomes Chapter 4 Global Climates and Biomes

Flood, Drought and Famine Global processes drive rainfall patterns Rainfall in the tropics is closely tied to the seasonal position of the sun Sun strikes earth directly, water evaporates and forms clouds that drop heavy rain. Sun is directly over the equator March 21 and September 22 Because Kenya is at the equator, heavy rain usually is dropped during April/May. As the sun moves north, it continues to drop rain. 2003, rain clouds did not mover northward and this resulted in bad floods in West Kenya and severe droughts in Northern Kenya Devastating consequences occurred

West Kenya Floods and North Kenya Droughts

I. 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. Location on the globe determines climate - 30°S or 30°N of equator get less rain, close to equator more rain.

Weather and Climate

I. Global Processes Determine Weather and Climate Regional differences in temperature and precipitation helps determine what organisms live there. Factors that affect the distribution of heat and precipitation: Unequal heating of the earth by the sun Atmospheric convection currents Rotation of the earths orbit around the sun and tilted axis and ocean currents

A. Earth's Atmosphere 5 layers of Gases and gravity keeps layers in place 1. Troposphere- the layer closest to Earth's surface extending roughly 16 km (10 miles) above Earth. - Densest layer - Mostly nitrogen, oxygen and water vapor - Air temperature decreases with distance from earth and varies with latitude.

Earth's Atmosphere 2. Stratosphere- above the troposphere, this extends from roughly 16 to 50 km (10-31 miles). - Less dense since farther from earth and less gravitational pull. - Ozone – pale blue gas composed of 3 oxygen atoms. - Forms a layer within the Stratosphere. - Absorbs most of the suns ultraviolet radiation. - UV radiation can cause DNA damage and cancer. - Stratospheric ozone layer critical for protection for our planet.

Tropospheric Ozone Stratospheric Ozone Difference between Tropospheric Ozone and Stratospheric Ozone Tropospheric Ozone Ozone in the troposphere is a photochemical pollutant Harmful to plants and animals Ozone is a secondary pollutant. It is not emitted but is formed in the atmosphere as a result of emissions of primary pollutants such as nitrogen oxides NOX. Ozone forms as a result of the emissions of primary pollutant and the presence of sunlight. If there is an abundance of NOX in the atmosphere ozone forms (smog) Stratospheric Ozone Ozone occurs I the stratosphere naturally. this layer protects us from UV light damage. Ozone hole or depletion over the Antarctic is caused by CFC’s Chlorofluorocarbons – damage the ozone – found in refrigerants Sine 1987 most of the world has stopped the use. Montreal Protocol – signed in 1987 by 24 nations to reduce CFC’s

3. Mesophere, 4. thermoshpere and 5 3. Mesophere, 4.thermoshpere and 5. exosphere are farthest and less dense from the earth Thermosphere important because it blocks X-ray and UV radiation. This is where Aurora borealis (north) and Aurora australis (south) Charged gas molecules that when hit by solar energy start to glow Driven by magnetic forces at the North and South Pole – best place to see.

Northern Lights

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.

Unequal Heating of Earth has 3 Primary Causes This unequal heating is because: 1. The variation in angle at which the Sun's rays strike the earth. (equator strike is at right angle) As a result suns rays travel a shorter distance through atmosphere to reach the surface in tropics. So more solar radiation reaches these areas that are closer.

Unequal Heating of Earth has 3 Primary Causes This unequal heating is because: 2. Variation in the amount of surface area over which the Sun's rays are distributed. Ex. Suns rays in the tropics are over a smaller surface area so tropics receive more solar energy per square meter.

Unequal Heating of Earth has 3 Primary Causes This unequal heating is because: 3. Some areas of Earth reflect more solar energy than others. (Albedo). The higher the Albedo of a surface the more solar energy is reflected and less absorbed. White surfaces have higher Albedo, so at the poles. Ex. Earths average Albedo is 30%, tropics 10- 20% and Poles 80-95%.

Atmospheric Convection Currents 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. Saturation Point – is the max amount of water vapor the air can hold. Decrease temperature decreases saturation point – water vapor condenses into liquid, clouds form and precipitation occurs.

Atmospheric Convection Currents 3. Adiabatic heating or cooling- as air rises in the atmosphere its pressure decreases and the air expands. Conversely, as air sinks, the pressure increases and the air decreases in volume. 4. Latent heat release- Production of heat when water vapor in the atmosphere condenses into liquid water from gas and energy is released.

Formation of Convection Currents Tropics: Warm humid air decreases in density, so air rises Rising air experiences lower pressure and adiabiatic cooling occurs Cooling causes air to reach saturation point Clouds form and precipitation occurs Condensations causes latent heat release which offsets adiabiatic cooling and air expands

Formation of Convection Currents Rising more rapidly, air flows upward from the tropics to troposphere Air near tropics is chilled, contains little water vapor As warm air rises from below the cold dry air is displaced horizontally both north and south of equator. Displaced air sinks back to earth, high pressure reduces its volume causing adiabiatic heating. When air reaches earth it is hot and dry and results in deserts. Desert air moves along earths surface back toward equator to replace air rising there, completes the circle.

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- the area of Earth that receives the most intense sunlight and where the ascending branches of the two Hadley cells converge. 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)

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Earth's Rotation and the Coriolis Effect Earths rotation affects direction of prevailing winds. Speed of the Earth’s rotation varies with latitude As Earth rotates, its surface moves much faster at the equator than in mid-latitude and polar regions. The faster rotation speeds closer to the equator cause a deflection of objects that are moving directly north or south.

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 Atmospheric convection currents Coriolis effect.

Hadley Cells and Trade Winds North of the equator, the Hadley Cells produces the Northeast Trade Winds. Come from the northeast. South of the equator, the Hadley Cells produce the South East Trade Winds, come from the southeast.

Coriolis Effect, Westerlies and Easterlies The Coriolis effect explains the prevailing winds in the mid-lat. 30° to 60° Westerlies – North of the 30° prevailing winds from the south west. Southern Hemisphere prevailing winds from the northwest. Easterlies – winds out of the northeast and southeast.

Earth's Tilt and the Seasons Most regions of the world experiance seasonal change due to earths tilt. The Earth's axis of rotation is tilted 23.5 ˚ When the Northern Hemisphere is tilted toward the Sun, the Southern Hemisphere is tilted away from the Sun, and vice versa.

Ocean Currents Ocean currents are driven by a combination of temperature, gravity, prevailing winds, the Coriolis effect, and the locations of continents. Tropics - Warm water, like warm air, expands and rises and flows away from the equator. Each of the 5 ocean basins contain a gyre driven by trade winds in the tropics and Westerlies at mid-latitude. 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.

Upwelling When currents diverge they cause upwelling. West Coast of most continents – upwhelling occurs. 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.

Thermohaline Circulation Thermohaline circulation- another oceanic circulation that drives the mixing of surface water and deep water. Important for moving heat and nutrients around the globe. Thermohaline circulation appears to be driven by surface waters that contain large amounts of salt. Caused by difference in salt and temperature.

Thermohaline Circulation

Thermohaline Circulation Warm water 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. For example, The Gulf Stream brings warm waters North East towards Europe. Brings large amounts of heat energy. England's average winter temperature is approximately 20 ˚ C (36˚F) warmer than Newfoundland, Canada, which is located at a similar latitude. Concern – global warming and increased air temperature could accelerate melting of glaciers in Northern Hemisphere by making the water diluted and less saltier, then it will not sink. This could shut down the thermohaline circulation. con

El Nino-Southern Oscillation Every 3 to 7 years, the interaction of the Earth's atmosphere and ocean cause surface currents in the tropical Pacific Ocean to reverse direction. Warm equatorial water from west pacific moves eastward toward the west coast of South America. First, the trade winds near South America weaken. This weakening allows warm equatorial water from the western Pacific to move eastward toward the west coast of South America. 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. These periodic changes in wind and ocean currents are collectively called the EL Nino-Southern Oscillation, or ENSO.

Rain Shadows When 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 and precipitation falls. The presence of the mountain range causes large amounts of precipitin to fall on its windward side. The cold, dry air 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 air is now war and dry and process arid conditions on the leeward side forming the region called a rain shadow.

Rain Shadows