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Chapter 3: Weather and Climate SECTION ONE: EARTH-SUN RELATIONSHIP Climate and Weather 1. Weather is the condition of the atmosphere in one place over a short period of time. 2. Climate is the average weather conditions averaged over many years. 3. The most important factor in determining the climate of an area is earth’s position in relation to the Sun. Earth’s position in relation to the sun. Earth’s Tilt and Rotation 1. The earth’s axis is an imaginary line that runs through the center of the earth between the North and South Poles. 2. The earth is tilted on its axis at about 23 ½ °. 3. Because the earth is tilted on its axis, not all places on earth receive the same amount of sunlight at the same time. 4. The most common scale for measuring temperature are Fahrenheit(°F) and Celcius (°C). Earth’s Tilt Earth’s Revolution 1. The earth rotates on its axis every 24 hours and revolves around the sun every 365 ¼ days. 2. The Earth’s revolution and tilt affect the amount of sunlight that reaches different locations on earth at different times of the year. 3. When the North Pole is tilted towards the sun, it is summer in the northern hemisphere. When the North Pole is tilted away from the sun, it is winter in the northern hemisphere. Winter Solstice-Northern Hemisphere 4. The seasons are reversed north and south of the equator. When it is summer in the northern hemisphere, it will be Winter in the southern hemisphere. When it is spring in the northern hemisphere, it is Fall in the southern hemisphere. 5. Twice a year (March 21 and September 23) the direct sunlight falls on the equator. This day is called an equinox, meaning “equal night,” because daytime and nighttime hours are equal. Equal amounts of sunlight reach the northern and southern hemispheres. Equinox 6. On June 21, the sun’s direct rays strike the Tropic of Cancer at 23 ½ ° North, bringing the longest day of the year in the Northern Hemisphere. This day is called the summer solstice and marks the beginning of the summer season in the Northern Hemisphere. 7. On September 23, the suns most direct rays strike the equator, marking the end of summer and the beginning of fall or Autumn. 8. As the earth continues in its revolution, the direct rays of the sun eventually strike the Tropic of Capricorn at 23 ½ ° South. This brings the shortest day of the year and the beginning of the winter solstice in the Northern Hemisphere. Solstice and Equinox 9. For six months of the year, one pole will receive almost 24 hours of continuous sunlight each day while the other pole receives almost no sunlight. 10. Continuous sunlight, a phenomenon known as midnight sun is caused by the tilt of the earth’s axis as it revolves around the sun. Midnight Sun Winter Solstice Antarctica 24 hours of darkness The Greenhouse Effect 1. The earth’s atmosphere reflects some of the suns radiation back into space. Enough radiation reaches earth’s surface to warm the air, land, and water. 2. Once Earth’s surface absorbs this radiation from the sun and is warmed, it then radiates this heat back into the atmosphere. 3. The earth’s atmosphere provides just about the right amount of insulation to promote life on the planet. 4. The 50% of the sun’s radiation that reaches the earth is converted into infrared radiation, or heat. 5. Clouds and greenhouse gases such as water vapor, methane, and carbon dioxide absorb the heat energy and trap it so that most of it cannot escape back into space. 6. The atmosphere is like a greenhouse in that it traps enough radiation to warm the land, water, and air and help plants grow, while reflecting some radiation to ensure that the earth does not overheat. 7. This greenhouse effect is the warming of the earth that occurs when sun’s radiation passes through the atmosphere, is absorbed by the earth, and is radiated as heat back into the atmosphere where it cannot escape back into space. 8. Without the greenhouse effect, Earth’s average temperature would be below 0°F and life as we know it would not exist. 9. According to the laws of physics, what would happen if the Earth gave back less energy than it received from the sun? 10. What would happen if the Earth gave back more heat energy than it received from the sun? 11. What would Earth be like if no greenhouse effect existed in our atmosphere? 12. Which places on earth receive the most direct sunlight? How does this affect their climates? 13. What is the northernmost line of latitude to receive the direct radiation from the sun? 14. What is the southernmost line of latitude to receive the direct radiation from the sun? Global Warming 15. Some scientist claim that rising carbon dioxide levels in Earths atmosphere may be linked to rising average global temperatures. This trend is known as global warming and may be linked to human activities such as the burning of fossil fuels, deforestation, and the release of methane gas. 16.What are some possible future effects of global warming? 17. What are some ways to reduce the human impact on global warming? Section 2: Factors Affecting Climates Climates are influenced by latitude, elevation, wind and ocean currents, mountain ranges, and a places location in relation to large bodies of water. Latitude, Climate, and Elevation: Because of Earth’s revolution around the sun, climates can be found in predictable patterns or zones of latitude. World Climate Patterns Low Latitudes The low latitude climate zone, also called the tropics, is between 30°S and 30°N. This includes the Tropics of Cancer and Capricorn and the Equator. This area receives direct rays from the sun and therefore have warm to hot climates. Low Latitude ClimatesTropics Low Latitudes-Tropics High Latitudes The high latitude zone includes Earth’s polar areas, which are located between 60° to 90°N and 60° to 90°S. When either the Northern or Southern Hemispheres are tilted towards the sun, its polar areas receive continuous, but indirect sunlight. These latitude zones are the coldest on earth. High latitudes-Polar Region Mid Latitudes The Mid latitude zones, between 30° to 60° North and 30° to 60° South, have temperate climates ranging from hot to cold. The mid-latitude climates have the most dramatic seasonal weather changes. Mid Latitude- Temperate Elevation Affects Climates Elevation, or height above sea level, has a major influence on climates because of the relationship between elevation and Temperature. As elevation increases, the temperature will decrease. This is because the earth’s atmosphere thins as altitude increases. The less dense the air is, the less heat it will retain. As elevation increases, temperatures decreases by about 3.5°F for every 1000 feet. As Elevation increases, Temperature decreases. Wind and Ocean Currents: Air moving across the surface of the earth is called Wind. Winds occur because sunlight heats the atmosphere and the surface of the earth unevenly. Warm temperatures cause the air to expand, become lighter, and rise into the atmosphere creating areas of low pressure. Cool temperatures cause air to sink in the atmosphere, creating areas of high pressure. Warm Air Rises Prevailing Winds Wind and Air Pressure Air moves from areas of high pressure to areas of low pressure, so the cooler air sinks to replace the warmer rising air. These movements of air cause winds to distribute the sun's energy, or heat around the planet. Air moves from High to Low Pressure Ocean currents Ocean currents also help distribute energy around the planet. These Ocean currents are usually cold or warm streams of seawater that flow in a circular pattern in the ocean. As they circulate, cold water from polar areas moves slowly toward the Equator. Warm water moves away from the equator into cooler water. Ocean Currents Patterns of wind and ocean currents: As winds blow because of pressure differences on Earth’s surface, warm tropical air moves toward the poles and cool polar air moves toward the equator. This movement of air creates the global winds that blow in fairly constant patterns, called prevailing winds. The Coriolis Effect The direction of prevailing winds is determined by latitude and is also affected by the Earth’s movement. As the Earth rotates from West to East, the paths of the prevailing winds are bent to the right in the northern hemisphere and to the left in the southern hemisphere. This phenomenon is called the Coriolis effect and causes winds to blow diagonally. Trade Winds Winds are generally named for the direction from which they blow. The prevailing winds of the lowlatitudes were called Trade Winds because they moved early trading ships. They blow from about 30° northeast and southwest towards the Equator. Prevailing Winds Westerlies and Polar Easterlies Westerlies are the prevailing winds in the midlatitudes. They blow from west to east between 30° to 60° north and south of the equator. In the high latitudes, Polar easterlies blow diagonally from east to west, pushing cold air towards the mid-latitudes. Doldrums Near the equator, warm air rises leaving a narrow, generally windless band of calm air called the Doldrums. Doldrums and Horse Latitudes Horse Latitudes Just north of the Tropic of Cancer and south of the Tropic of Capricorn are two windless bands caused by high pressure air sinking back to the earth. In the days of sailing ships, these windless areas were feared by sailors because they could become stranded without the prevailing winds to power their ships. To lighten the load of ships caught in these windless zones, sailors often had to lighten the load of the ships by dumping cargo, such as livestock into the ocean. The Horse Latitudes, the calm areas at the edge of the tropics, derived their name from this practice. Ocean currents and the Coriolis Effect Cold and warm ocean currents move in patterns in the ocean similar to the patterns of wind movement. Ocean currents are caused by many of the same factors that cause winds including Earth’s rotation air pressure, and differences in water temperature. The Coriolis Effect also affects ocean currents. Coriolis Effect Warm and Cold Ocean Currents Cold ocean currents generally flow on the west coast of continents and cool the coastal land areas. Warm ocean currents generally flow on the East coast of continents and bring warmer temperatures and humidity to coastal areas they pass. A good example of this is the North Atlantic Drift that carries warm water to the west coast of Europe creating a mild climate in spite of its northern latitude. Influences on Weather: Water vapor forms in the atmosphere from evaporated surface water. The high temperature causes the air to rise. As the air rises, it cools, condenses into clouds, and then releases water droplets in the form of precipitation. Temperature’s effect on Precipitation Warm air is able to hold more water vapor, so as warm air rises and cools, it eventually will reach a temperature in which the air is unable to hold it as a vapor or clouds any longer. At this point the air is saturated and gravity pulls the water droplets back to Earth as precipitation. El Nino El Nino is a periodic change in the pattern of ocean currents, water temperatures, and weather in the mid-Pacific. El Nino does not occur every year, but has increased in frequency since the 1970’s. In an El Nino year, prevailing winds and ocean currents may reverse direction, causing warm water to spread along the coasts of Ecuador, Peru, and Chile. El Nino’s Effects These changes in the Pacific influence climates around the world. Precipitation increases along the coasts of North and South America, making the winters warmer and increasing the risk of Flooding. In Southeast Asia and Australia, drought and forest fires occur. Winter rains are heavier along the west coast of North America. El Nino Flooding in South America Landforms and Climate: Large bodies of water are slower to heat and cool, so they tend to keep temperatures in surrounding lands moderate. Coastal lands often experience less changeable weather as a result of this. The interiors of continents tend to experience extremes in seasonal temperatures. Gobi Desert Rain Shadow Effect Mountain ranges affect climates. Increases in elevation bring decreases in temperature. Mountain ranges push wind upward. The rising air cools releasing moisture in the form of Precipitation. Most of the precipitation falls on the Windward side of the mountain, or the side facing the wind. Rain Shadow Desert After the precipitation is released, winds become warmer and dryer as they descend on the leeward or opposite side of the mountain. The hot dry air produces little precipitation in an effect known as Rain Shadow Effect. The rain shadow often causes dry areas, and even deserts to develop on the leeward side of a mountain range. Chapter 3, Section 3: World Climate Patterns, Climate Regions, and Biomes Climate Regions and Biomes Climates are organized into five climate zones: tropical, dry or (arid), mid-latitude or (temperate), high-latitude or (polar) and highland (mountains). Biomes, or ecosystems are defined by a specific community of plants and animals that inhabit a region. Biomes are classified into four main categories: forests, grasslands, deserts, and tundra. Earth’s Climate Zones Earth’s Biomes Biomes Biomes are affected by climate and terrain, or physical characteristics of the surface of the land. The key influences of climate are temperature, precipitation, and latitude. Similarities in climates often result in similar biomes. For example, areas that receive large amounts of rain and have warm temperatures tend to have lush, green rain forests. These areas tend to be located near the equator. Tropical Climates: Tropical Climates are found in or near the low-latitudes in areas referred to as the tropics. Tropical Wet, or rain forest climates are warm, humid, and rainy year-round. Annual rainfall averages from 50-260 inches. This much rain tends to strip the soil of nutrients. The biome in these climates are the tropical rain forests, characterized by thick vegetation that grows in layers. Tall trees form a canopy over shorter trees and bushes, and shade-loving bushes grow on the forest floor. Rain Forest Amazon Rain Forest The world’s largest rain forest is in the Amazon River Basin. Scientists estimate that more than half of all the plant and animal species in the world are found in tropical rain forests. Tropical Wet/Dry Climates Tropical Wet/Dry climates have very distinct wet and dry seasons, with high year-round temperatures. Typically, summer is the wet season and winter is the dry season. These regions are called savanna biomes and scattered trees and grasslands are common vegetation. Large herds of grazing animals may be found in the savanna grasslands of Africa. Tropical Savanna Dry Climates: The two main types of dry climates are semi-arid (or steppe) and arid (or Desert). Steppe climates are usually located away from oceans or large bodies of water and are less-humid. These areas average between 10-30 inches of precipitation per year. Steppe grasslands have warm summers and very cold winters. The steppe biome has mainly dry grassland vegetation with very few trees. The largest steppe grassland in the world stretches from China and Mongolia in the East to Europe in the West. Steppe Grassland Deserts Deserts are extremely dry areas that receive about 10 inches of precipitation or less per year and support a very small amount of plant and animal life. Only plants that can live without much water and tolerate extreme temperatures live in desert climates. Most deserts are hot and dry, although some can be extremely cold. Some deserts have underground springs that support an oasis, or area of lush vegetation. Desert Biome Deserts Desert temperatures tend to vary widely from day to night because of the lack of humidity (or moisture) in the air. A band of deserts are distributed around the world near 30° latitude because this is where high pressure air sinks back to the earth creating clear, stable weather. Deserts may also be found on the west coast of continents near cold ocean currents. Distribution of Deserts Mid-Latitude Climates (30°60°): Humid subtropical Humid Continental Marine West Coast Mediterranean. Humid Subtropical Humid subtropical climates have short, mild winters, hot and humid summers and year-round rain. The southeastern part of the U.S. experiences this type of climate. Prevailing winds from the Gulf of Mexico keep this region warm and humid. Vegetation in this region consists of prairies and mixed deciduous and coniferous forests. Coniferous trees are evergreen and have cones. Deciduous trees have broad leaves that change color and drop from the trees in the fall. Humid Subtropical Deciduous Trees Coniferous Trees Marine West Coast Marine West Coast climates can be found on the Southern coast of Chile, Australia, the British Isles, and the Pacific coast of North America. Ocean winds bring cool summers and cool, rainy winters. The abundance of rainfall supports both coniferous and deciduous forests. Seattle, Washington experiences this type of climate. Marine West Coast Mediterranean Climates Mediterranean climates can be found surrounding the Mediterranean Sea, central California, and the Southwestern coast of Australia. These areas experience mild, rainy winters and hot, dry summers. The natural vegetation includes thickets of woody bushes and short trees known as Mediterranean shrub, or chaparral vegetation. Grapes, olives, and citrus fruits are common crops grown in these regions. Mediterranean Biomes Humid Continental Climates Humid continental climates are found on the eastern part of continents in the upper middlelatitudes. Winters can be severely cold the further north the location and summers can be warm. This climate experiences the most extreme change of seasons and weather patterns. The natural vegetation will be mixed deciduous and coniferous forests. The most-northern parts of this region are mostly coniferous forests. Humid Continental Climates Humid Continental Climate High-Latitude Climates: In the high-latitudes, freezing temperatures are common all year because of the lack of direct sunlight. As a result, the amount and variety of vegetation is limited. Subarctic Climates Just south of the Arctic Circle are the subarctic climate regions. Winters here are bitterly cold and summers are short and cool. In parts of the subarctic, only a thin layer of topsoil thaws, leaving a permanently frozen subsoil called, permafrost. Needle-leaf evergreen (or coniferous trees), may be the dominant vegetation in this region. Taiga, Boreal, Coniferous Forest Tundra Climates Closer to the poles are the Tundra climate regions. Winter darkness and bitter cold lasts for months. While summer has only limited warming. The permafrost prevents tree from growing here, so vegetation is limited to low bushes, short grasses, lichens, mosses, and some flowers. Tundra Vegetation Ice Cap Climates Ice cap climates cover the poles. Snow and ice can reach 2 miles thick and lichens may be the only vegetation. Temperatures average below freezing every month. Ice Cap Highland Climates Highland, or mountain climates vary with elevation. The lower elevation regions of mountains have warmer climates and the higher elevations have colder climates. Each climate zone is suitable for different vegetation and animals. Highland Climates Extreme weather and climates: Hurricanes are westward moving tropical storms caused by warm air rising from the warm waters near the equator. High winds, flooding, and loss of lives result from hurricanes. Most deaths are caused by the storm surge. Hurricanes have sustained wind speeds of at least 72 mph. Monsoons Monsoons are seasonal shifts in wind that cause dry seasons in the winter and flooding in the summer in large areas of South Asia (India) and Southeast Asia. Tornados Tornados are violently rotating columns of air that result from a large thunderstorms called a super cell. There are more tornados in the area of the United States called tornado alley, than any other region of the world. Drought Droughts are long periods of low rainfall totals resulting in desertification and loss of agriculture. California is currently experiencing a severe drought.