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L_0026 | changing weather | T_0265 | When cold air masses move south from the poles, they run into warm air masses moving north from the tropics. The boundary between two air masses is called a front. Air masses usually dont mix at a front. The differences in temperature and pressure cause clouds and precipitation. Types of fronts include cold, warm, occluded, and stationary fronts. | text | null |
L_0026 | changing weather | T_0266 | A cold front occurs when a cold air mass runs into a warm air mass. This is shown in Figure 16.7. The cold air mass moves faster than the warm air mass and lifts the warm air mass out of its way. As the warm air rises, its water vapor condenses. Clouds form, and precipitation falls. If the warm air is very humid, precipitation can be heavy. Temperature and pressure differences between the two air masses cause winds. Winds may be very strong along a cold front. As the fast-moving cold air mass keeps advancing, so does the cold front. Cold fronts often bring sudden changes in the weather. There may be a thin line of storms right at the front that moves as it moves. In the spring and summer, these storms may be thunderstorms and tornadoes. In the late fall and winter, snow storms may occur. After a cold front passes, the cold air mass behind it brings cooler temperatures. The air is likely to be less humid as well. Can you explain why? | text | null |
L_0026 | changing weather | T_0267 | When a warm air mass runs into a cold air mass it creates a warm front. This is shown in Figure 16.8. The warm air mass is moving faster than the cold air mass, so it flows up over the cold air mass. As the warm air rises, it cools, resulting in clouds and sometimes light precipitation. Warm fronts move slowly and cover a wide area. After a warm front passes, the warm air mass behind it brings warmer temperatures. The warm air is also likely to be more humid. | text | null |
L_0026 | changing weather | T_0268 | With an occluded front, a warm air mass becomes trapped between two cold air masses. The warm air is lifted up above the cold air as in Figure 16.9. Cloudy weather and precipitation along the front are typical. | text | null |
L_0026 | changing weather | T_0269 | Sometimes two air masses stop moving when they meet. These stalled air masses create a stationary front. Such a front may bring clouds and precipitation to the same area for many days. | text | null |
L_0026 | changing weather | T_0270 | Cold air is dense, so it sinks. This creates a center of high pressure. Warm air is less dense so it rises. This creates a center of low pressure. Air always flows from higher to lower pressure. As the air flows, Earths surface rotates below it causing Coriolis effect. So while the wind blows into the low pressure, it revolves in a circular pattern. This wind pattern forms a cyclone. The same happens while the wind blows out of a high pressure. This forms an anticyclone. Both are shown in Figure 16.10. A cyclone is a system of winds that rotates around a center of low pressure. Cyclones bring cloudy, wet weather. An anticyclone is a system of winds that rotates around a center of high pressure. Anticyclones bring fair, dry weather. | text | null |
L_0027 | storms | T_0271 | A storm is an episode of severe weather caused by a major disturbance in the atmosphere. Storms can vary a lot in the time they last and in how severe they are. A storm may last for less than an hour or for more than a week. It may affect just a few square kilometers or thousands. Some storms are harmless and some are disastrous. The size and strength of a storm depends on the amount of energy in the atmosphere. Greater differences in temperature and air pressure produce stronger storms. Types of storms include thunderstorms, tornadoes, hurricanes, and winter storms such as blizzards. | text | null |
L_0027 | storms | T_0272 | Thunderstorms are are known for their heavy rains and lightning. In strong thunderstorms, hail and high winds are also likely. Thunderstorms are very common. Worldwide, there are about 14 million of them each year! In the U.S., they are most common and strongest in the Midwest. | text | null |
L_0027 | storms | T_0273 | Thunderstorms occur when the air is very warm and humid. The warm air rises rapidly to create strong updrafts. When the rising air cools, its water vapor condenses. The updrafts create tall cumulonimbus clouds called thunder- heads. You can see one in Figure 16.12. | text | null |
L_0027 | storms | T_0274 | During a thunderstorm, some parts of a thunderhead become negatively charged. Other parts become positively charged. The difference in charge creates lightning. Lightning is a huge release of electricity. Lightning can jump between oppositely charged parts of the same cloud, between one cloud and another, or between a cloud and the ground. You can see lightning in Figure 16.13. Lightning blasts the air with energy. The air heats and expands so quickly that it explodes. This creates the loud sound of thunder. Do you know why you always hear the boom of thunder after you see the flash of lightning? Its because light travels faster than sound. If you count the seconds between seeing lightning and hearing thunder, you can estimate how far away the lightning was. A lapse of 5 seconds is equal to about a mile. | text | null |
L_0027 | storms | T_0275 | Severe thunderstorms have a lot of energy and strong winds. This allows them to produce tornadoes. A tornado is a funnel-shaped cloud of whirling high winds. You can see a tornado in Figure 16.14. The funnel moves along the ground, destroying everything in its path. As it moves it loses energy. Before this happens it may have gone up to 25 kilometers (16 miles). Fortunately, tornadoes are narrow. They may be only 150 meters (500 feet) wide. | text | null |
L_0027 | storms | T_0276 | The winds of a tornado can reach very high speeds. The faster the winds blow, the greater the damage they cause. Wind speed and damage are used to classify tornadoes. Table 16.1 shows how. F Scale F0 (km/hr) 64-116 (mph) 40-72 F1 117-180 73-112 Damage Light - tree branches fall and chimneys may col- lapse Moderate - mobile homes, autos pushed aside F Scale F2 (km/hr) 181-253 (mph) 113-157 F3 254-332 158-206 F4 333-419 207-260 F5 420-512 261-318 F6 >512 >318 Damage Considerable - roofs torn off houses, large trees up- rooted Severe - houses torn apart, trees uprooted, cars lifted Devastating - houses lev- eled, cars thrown Incredible - structures fly, cars become missiles Maximum tornado wind speed | text | null |
L_0027 | storms | T_0277 | Look at the map in Figure 16.15. It shows where the greatest number of tornadoes occur in the U.S. Tornadoes can happen almost anywhere in the U.S. but only this area is called tornado alley. Why do so many tornadoes occur here? This is where warm air masses from the south run into cold air masses from the north. | text | null |
L_0027 | storms | T_0278 | Tornadoes may also come from hurricanes. A hurricane is an enormous storm with high winds and heavy rains. Hurricanes may be hundreds of kilometers wide. They may travel for thousands of kilometers. The storms wind speeds may be greater than 251 kilometers (156 miles) per hour. Hurricanes develop from tropical cyclones. Hurricanes form over warm very ocean water. This water gives them their energy. As long as a hurricane stays over the warm ocean, it keeps growing stronger. However, if it goes ashore or moves over cooler water, it is cut off from the hot water energy. The storm then loses strength and slowly fades away. | text | null |
L_0027 | storms | T_0279 | At the center of a hurricane is a small area where the air is calm and clear. This is the eye of the hurricane. The eye forms at the low-pressure center of the hurricane. You can see the eye of a hurricane in Figure 16.16. | text | null |
L_0027 | storms | T_0280 | Like tornadoes, hurricanes are classified on the basis of wind speed and damage. Table 16.2 shows how. Category 1 (weak) Kph 119-153 Mph 74-95 2 (moderate) 154-177 96-110 3 (strong) 178-209 111-130 Damage Above normal; no real damage to structures Some roofing, door, and window damage, consid- erable damage to vegeta- tion, mobile homes, and piers Some buildings damaged; mobile homes destroyed Category 4 (very strong) Kph 210-251 Mph 131-156 5 (devastating) >251 >156 Damage Complete roof failure on small residences; major erosion of beach areas; major damage to lower floors of structures near shore Complete roof failure on many residences and in- dustrial buildings; some complete building failures | text | null |
L_0027 | storms | T_0281 | Some of the damage from a hurricane is caused by storm surge. Storm surge is very high water located in the low pressure eye of the hurricane. The very low pressure of the eye allows the water level to rise above normal sea level. Storm surge can cause flooding when it reaches land. You can see this in Figure 16.17. High winds do a great deal of damage in hurricanes. High winds can also create very big waves. If the large waves are atop a storm surge, the high water can flood the shore. If the storm happens to occur at high tide, the water will rise even higher. | text | null |
L_0027 | storms | T_0282 | Like hurricanes, winter storms develop from cyclones. But in the case of winter storms, the cyclones form at higher latitudes. In North America, cyclones often form when the jet stream dips south in the winter. This lets dry polar air pour south. At the same time, warm moist air from the Gulf of Mexico flows north. When the two air masses meet, the differences in temperature and pressure cause strong winds and heavy precipitation. Two types of winter storms that occur in the U.S. are blizzards and lake-effect snow storms. | text | null |
L_0027 | storms | T_0283 | A blizzard is a snow storm that has high winds. To be called a blizzard, a storm must have winds greater than 56 kilometers (35 miles) per hour and visibility of 14 mile or less because of wind-blown snow. You can see a blizzard in Figure 16.18. Blizzards are dangerous storms. The wind may blow the snow into deep drifts. Along with the poor visibility, the snow drifts make driving risky. The wind also makes cold temperatures more dangerous. The greater the wind speed, the higher the windchill. Windchill is what the temperature feels like when the wind is taken into account. It depends on air temperature and wind speed, as you can see in Figure 16.19. Higher windchill will cause a person to suffer frostbite and other harmful effects of cold sooner than if the wind isnt blowing. | text | null |
L_0027 | storms | T_0284 | Some places receive very heavy snowfall just about every winter. If they are near a lake, they may be getting lake- effect snow. Figure 16.20 shows how lake-effect snow occurs. Winter winds pick up moisture as they pass over the relatively warm waters of a large lake. When the winds reach the cold land on the other side, the air cools. Since there was so much moisture in the air it can drop a lot of snow. More than 254 centimeters (100 inches) of snow may fall in a single lake-effect storm! | text | null |
L_0028 | weather forecasting | T_0285 | Weather is very difficult to predict. Thats because its very complex and many factors are involved. Slight changes in even one factor can cause a big change in the weather. Still, certain rules of thumb generally apply. These rules help meteorologists forecast the weather. For example, low pressure is likely to bring stormy weather. So if a center of low pressure is moving your way, you can expect a storm. | text | null |
L_0028 | weather forecasting | T_0286 | Predicting the weather requires a lot of weather data. Technology is used to gather the data and computers are used to analyze the data. Using this information gives meteorologists the best chance of predicting the weather. | text | null |
L_0028 | weather forecasting | T_0287 | Weather instruments measure weather conditions. One of the most important conditions is air pressure, which is measured with a barometer. Figure 16.23 shows how a barometer works. There are also a number of other commonly used weather instruments (see Figure 16.24): A thermometer measures temperature. An anemometer measures wind speed. A rain gauge measures the amount of rain. A hygrometer measures humidity. A wind vane shows wind direction. A snow gauge measures the amount of snow. | text | null |
L_0028 | weather forecasting | T_0288 | Weather instruments collect data from all over the world at thousands of weather stations. Many are on land but some float in the oceans on buoys. You can see what a weather station looks like in Figure 16.25. Theres probably at least one weather station near you. Other weather devices are needed to collect weather data in the atmosphere. They include weather balloons, satellites, and radar. You can read about them in Figure 16.25. Weather stations contain many instruments for measuring weather conditions. The weather balloon in Figure | text | null |
L_0028 | weather forecasting | T_0288 | Weather instruments collect data from all over the world at thousands of weather stations. Many are on land but some float in the oceans on buoys. You can see what a weather station looks like in Figure 16.25. Theres probably at least one weather station near you. Other weather devices are needed to collect weather data in the atmosphere. They include weather balloons, satellites, and radar. You can read about them in Figure 16.25. Weather stations contain many instruments for measuring weather conditions. The weather balloon in Figure | text | null |
L_0028 | weather forecasting | T_0289 | What do meteorologists do with all that weather data? They use it in weather models. The models analyze the data and predict the weather. The models require computers. Thats because so many measurements and calculations are involved. | text | null |
L_0028 | weather forecasting | T_0290 | You may have seen weather maps like the one in Figure 16.26. A weather map shows weather conditions for a certain area. The map may show the actual weather on a given day or it may show the predicted weather for some time in the future. Some weather maps show many weather conditions. Others show a single condition. | text | null |
L_0028 | weather forecasting | T_0291 | The weather map in Figure 16.26 shows air pressure. The lines on the map connect places that have the same air pressure. Air pressure is measured in a unit called the millibar. Isobars are the lines that connect the points with the same air pressure. The map also shows low- and high-pressure centers and fronts. Find the cold front on the map. This cold front is likely to move toward the northeast over the next couple of days. How could you use this information to predict what the weather will be on the East Coast? | text | null |
L_0028 | weather forecasting | T_0292 | Instead of air pressure, weather maps may show other weather conditions. For example, a temperature map might show the high and low temperatures of major cities. The map may have isotherms, lines that connect places with the same temperature. | text | null |
L_0029 | climate and its causes | T_0293 | Climate is the average weather of a place over many years. It includes average temperatures. It also includes average precipitation. The timing of precipitation is part of climate as well. What determines the climate of a place? Latitude is the main factor. A nearby ocean or mountain range can also play a role. | text | null |
L_0029 | climate and its causes | T_0294 | Latitude is the distance north or south of the equator. Its measured in degrees, from 0 to 90 . Several climate factors vary with latitude. | text | null |
L_0029 | climate and its causes | T_0295 | Temperature changes with latitude. You can see how in Figure 17.2 At the equator, the Suns rays are most direct. Temperatures are highest. At higher latitudes, the Suns rays are less direct. The farther an area is from the equator, the lower is its temperature. At the poles, the Suns rays are least direct. Much of the area is covered with ice and snow, which reflect a lot of sunlight. Temperatures are lowest here. | text | null |
L_0029 | climate and its causes | T_0296 | Global air currents affect precipitation. How they affect it varies with latitude. You can see why in Figure 17.3. | text | null |
L_0029 | climate and its causes | T_0297 | Global air currents cause global winds. Figure 17.4 shows the direction that these winds blow. Global winds are the prevailing, or usual, winds at a given latitude. The winds move air masses, which causes weather. The direction of prevailing winds determines which type of air mass usually moves over an area. For example, a west wind might bring warm moist air from over an ocean. An east wind might bring cold dry air from over a mountain range. Which wind prevails has a big effect on the climate. What if the prevailing winds are westerlies? What would the climate be like? | text | null |
L_0029 | climate and its causes | T_0298 | When a place is near an ocean, the water can have a big effect on the climate. | text | null |
L_0029 | climate and its causes | T_0299 | Even places at the same latitude may have different climates if one is on a coast and one is inland. On the coast, the climate is influenced by warm moist air from the ocean. A coastal climate is usually mild. Summers arent too hot, and winters arent too cold. Precipitation can be high due to the moisture in the air. Farther inland, the climate is influenced by cold or hot air from the land. This air may be dry because it comes from over land. An inland climate is usually more extreme. Winters may be very cold, and summers may be very hot. Precipitation can be low. | text | null |
L_0029 | climate and its causes | T_0300 | Ocean currents carry warm or cold water throughout the worlds oceans. They help to even out the temperatures in the oceans. This also affects the temperature of the atmosphere and the climate around the world. Currents that are near shore have a direct impact on climate. They may make the climate much colder or warmer. You can see examples of this in Figure 17.5. | text | null |
L_0029 | climate and its causes | T_0301 | Did you ever hike or drive up a mountain? Did you notice that it was cooler near the top? Climate is not just different on a mountain. Just having a mountain range nearby can affect the climate. | text | null |
L_0029 | climate and its causes | T_0302 | Air temperature falls at higher altitudes. You can see this in Figure 17.6. Why does this happen? Since air is less dense at higher altitudes, its molecules are spread farther apart than they are at sea level. These molecules have fewer collisions, so they produce less heat. Look at the mountain in Figure 17.7. The peak of Mount Kilimanjaro, Tanzania (Africa, 3 south latitude) is 6 kilometers (4 miles) above sea level. At 3 S its very close to the equator. At the bottom of the mountain, the temperature is high year round. How can you tell that its much cooler at the top? | text | null |
L_0029 | climate and its causes | T_0303 | Mountains can also affect precipitation. Mountains and mountain ranges can cast a rain shadow. As winds rise up a mountain range the air cools and precipitation falls. On the other side of the range the air is dry and it sinks. So there is very little precipitation on the far (leeward) side of a mountain range. Figure 17.8 shows how this happens. | text | null |
L_0032 | ecosystems | T_0324 | An ecosystem is a group of living things and their environment. The word ecosystem is short for ecological system. Like any system, an ecosystem is a group of parts that work together. You can see examples of ecosystems in Figure 18.1. The forest pictured is a big ecosystem. Besides trees, what living things do you think are part of the forest ecosystem? The dead tree stump in the same forest is a small ecosystem. It includes plants, mosses, and fungi. It also includes insects and worms. | text | null |
L_0032 | ecosystems | T_0325 | Abiotic factors are the nonliving parts of ecosystems. They include air, sunlight, soil, water, and minerals. These are all things that are needed for life. They determine which living things and how many of them an ecosystem can support. Figure 18.2 shows an ecosystem and its abiotic factors. | text | null |
L_0032 | ecosystems | T_0326 | Biotic factors are the living parts of ecosystems. They are the species of living things that reside together. | text | null |
L_0032 | ecosystems | T_0327 | A species is a unique type of organism. Members of a species can interbreed and produce offspring that can breed (they are fertile). Organisms that are not in the same species cannot do this. Examples of species include humans, lions, and redwood trees. Can you name other examples? Each species has a particular way of making a living. This is called its niche. You can see the niche of a lion in Figure 18.3. A lion makes its living by hunting and eating other animals. Each species also has a certain place where it is best suited to live. This is called its habitat. The lions habitat is a grassland. Why is a lion better off in a grassland than in a forest? | text | null |
L_0032 | ecosystems | T_0328 | All the members of a species that live in the same area form a population. Many different species live together in an ecosystem. All their populations make up a community. What populations live together in the grassland in Figure | text | null |
L_0032 | ecosystems | T_0329 | All ecosystems have living things that play the same basic roles. Some organisms must be producers. Others must be consumers. Decomposers are also important. | text | null |
L_0032 | ecosystems | T_0330 | Producers are living things that use energy to make food. Producers make food for themselves and other living things. There are two types of producers: By far the most common producers use the energy in sunlight to make food. This is called photosynthesis. Producers that photosynthesize include plants and algae. These organisms must live where there is plenty of sunlight. Which living things are producers in Figure 18.3? Other producers use the energy in chemicals to make food. This is called chemosynthesis. Only a very few producers are of this type, and all of them are microbes. These producers live deep under the ocean where there is no sunlight. You can see an example in Figure 18.4. | text | null |
L_0032 | ecosystems | T_0331 | Consumers cant make their own food. Consumers must eat producers or other consumers. Figure 18.5 lists the three main types of consumers. Which type are you? Consumers get their food in different ways Figure 18.6. Grazers feed on living organisms without killing them. A rabbit nibbles on leaves and a mosquito sucks a drop of blood. Predators, like lions, capture and kill animals for food. The animals they eat are called prey. Even some plants are consumers. Pitcher plants trap insects in their sticky fluid in their pitchers. The insects are their prey. Scavengers eat animals that are already dead. This hyena is eating the remains of a lions prey. Decomposers break down dead organisms and the wastes of living things. This dung beetle is rolling a ball of dung (animal waste) back to its nest. The beetle will use the dung to feed its young. The mushrooms pictured are growing on a dead log. They will slowly break it down. This releases its nutrients to the soil. | text | null |
L_0032 | ecosystems | T_0332 | All living things need energy. They need it to power the processes of life. For example, it takes energy to grow. It also takes energy to produce offspring. In fact, it takes energy just to stay alive. Remember that energy cant be created or destroyed. It can only change form. Energy changes form as it moves through ecosystems. | text | null |
L_0032 | ecosystems | T_0333 | Most ecosystems get their energy from the Sun. Only producers can use sunlight to make usable energy. Producers convert the sunlight into chemical energy or food. Consumers get some of that energy when they eat producers. They also pass some of the energy on to other consumers when they are eaten. In this way, energy flows from one living thing to another. | text | null |
L_0032 | ecosystems | T_0334 | A food chain is a simple diagram that shows one way energy flows through an ecosystem. You can see an example of a food chain in Figure 18.7. Producers form the base of all food chains. The consumers that eat producers are called primary consumers. The consumers that eat primary consumers are secondary consumers. This chain can continue to multiple levels. At each level of a food chain, a lot of energy is lost. Only about 10 percent of the energy passes to the next level. Where does that energy go? Some energy is given off as heat. Some energy goes into animal wastes. Energy also goes into growing things that another consumer cant eat, like fur. Its because so much energy is lost that most food chains have just a few levels. Theres not enough energy left for higher levels. | text | null |
L_0032 | ecosystems | T_0335 | Food chains are too simple to represent the real world. They dont show all the ways that energy flows through an ecosystem. A more complex diagram is called a food web. You can see an example in Figure 18.8. A food web consists of many overlapping food chains. Can you identify the food chains in the figure? How many food chains include the mouse? | text | null |
L_0032 | ecosystems | T_0336 | Living things need nonliving matter as well as energy. What do you think matter is used for? One thing is to build bodies. They also need it to carry out the processes of life. Any nonliving matter that living things need is called a nutrient. Carbon and nitrogen are examples of nutrients. Unlike energy, matter is recycled in ecosystems. You can see how in Figure 18.9. Decomposers release nutrients when they break down dead organisms. The nutrients are taken up by plants through their roots. The nutrients pass to primary consumers when they eat the plants. The nutrients pass to higher level consumers when they eat lower level consumers. When living things die, the cycle repeats. | text | null |
L_0032 | ecosystems | T_0336 | Living things need nonliving matter as well as energy. What do you think matter is used for? One thing is to build bodies. They also need it to carry out the processes of life. Any nonliving matter that living things need is called a nutrient. Carbon and nitrogen are examples of nutrients. Unlike energy, matter is recycled in ecosystems. You can see how in Figure 18.9. Decomposers release nutrients when they break down dead organisms. The nutrients are taken up by plants through their roots. The nutrients pass to primary consumers when they eat the plants. The nutrients pass to higher level consumers when they eat lower level consumers. When living things die, the cycle repeats. | text | null |
L_0093 | air masses | T_0914 | An air mass is a batch of air that has nearly the same temperature and humidity (Figure 1.1). An air mass acquires these characteristics above an area of land or water known as its source region. When the air mass sits over a region for several days or longer, it picks up the distinct temperature and humidity characteristics of that region. | text | null |
L_0093 | air masses | T_0915 | Air masses form over a large area; they can be 1,600 km (1,000 miles) across and several kilometers thick. Air masses form primarily in high pressure zones, most commonly in polar and tropical regions. Temperate zones are ordinarily too unstable for air masses to form. Instead, air masses move across temperate zones, so the middle latitudes are prone to having interesting weather. The source regions of air masses found around the world. Symbols: (1) origin over a continent (c) or an ocean (m, for maritime); (2) arctic (A), polar (P,) tropical (T), and equatorial (E); (3) properties relative to the ground it moves over: k, for colder, w for warmer. What does an air mass with the symbol cPk mean? The symbol cPk is an air mass with a continental polar source region that is colder than the region it is now moving over. | text | null |
L_0093 | air masses | T_0916 | Air masses are slowly pushed along by high-level winds. When an air mass moves over a new region, it shares its temperature and humidity with that region. So the temperature and humidity of a particular location depends partly on the characteristics of the air mass that sits over it. | text | null |
L_0093 | air masses | T_0917 | Storms arise if the air mass and the region it moves over have different characteristics. For example, when a colder air mass moves over warmer ground, the bottom layer of air is heated. That air rises, forming clouds, rain, and sometimes thunderstorms. How would a moving air mass form an inversion? When a warmer air mass travels over colder ground, the bottom layer of air cools and, because of its high density, is trapped near the ground. | text | null |
L_0093 | air masses | T_0918 | In general, cold air masses tend to flow toward the Equator and warm air masses tend to flow toward the poles. This brings heat to cold areas and cools down areas that are warm. It is one of the many processes that act to balance out the planets temperatures. Click image to the left or use the URL below. URL: | text | null |
L_0100 | biological communities | T_0946 | A population consists of all individuals of a single species that exist together at a given place and time. A species is a single type of organism that can interbreed and produce fertile offspring. All of the populations living together in the same area make up a community. | text | null |
L_0100 | biological communities | T_0947 | An ecosystem is made up of the living organisms in a community and the nonliving things, the physical and chemical factors, that they interact with. The living organisms within an ecosystem are its biotic factors (Figure 1.1). Living things include bacteria, algae, fungi, plants, and animals, including invertebrates, animals without backbones, and vertebrates, animals with backbones. (a) The horsetail Equisetum is a primitive plant. (b) Insects are among the many different types of invertebrates. (c) A giraffe is an example of a vertebrate. Physical and chemical features are abiotic factors. Abiotic factors include resources living organisms need, such as light, oxygen, water, carbon dioxide, good soil, and nitrogen, phosphorous, and other nutrients. Nutrients cycle through different parts of the ecosystem and can enter or leave the ecosystem at many points. Abiotic factors also include environmental features that are not materials or living things, such as living space and the right temperature range. Energy moves through an ecosystem in one direction. Click image to the left or use the URL below. URL: | text | null |
L_0100 | biological communities | T_0948 | Organisms must make a living, just like a lawyer or a ballet dancer. This means that each individual organism must acquire enough food energy to live and reproduce. A species way of making a living is called its niche. An example of a niche is making a living as a top carnivore, an animal that eats other animals, but is not eaten by any other animals (Figure 1.2). Every species fills a niche, and niches are almost always filled in an ecosystem. The top carnivore niche is filled by lions on the savanna. Click image to the left or use the URL below. URL: | text | null |
L_0100 | biological communities | T_0949 | An organisms habitat is where it lives (Figure 1.3). The important characteristics of a habitat include climate, the availability of food, water, and other resources, and other factors, such as weather. | text | null |
L_0101 | blizzards | T_0950 | A blizzard is distinguished by certain conditions: Temperatures below -7 C (20 F); -12 C (10 F) for a severe blizzard. Winds greater than 56 kmh (35 mph); 72 kmh (45 mph) for a severe blizzard. Snow so heavy that visibility is 2/5 km (1/4 mile) or less for at least three hours; near zero visibility for a severe blizzard. | text | null |
L_0101 | blizzards | T_0951 | Blizzards happen across the middle latitudes and toward the poles, usually as part of a mid-latitude cyclone. Bliz- zards are most common in winter, when the jet stream has traveled south and a cold, northern air mass comes into contact with a warmer, semitropical air mass (Figure 1.2). The very strong winds develop because of the pressure gradient between the low-pressure storm and the higher pressure west of the storm. Snow produced by the storm gets caught in the winds and blows nearly horizontally. Blizzards can also produce sleet or freezing rain. A blizzard obscures the Capitol in Wash- ington, DC. Blizzard snows blanket the East Coast of the United States in February 2010. | text | null |
L_0101 | blizzards | T_0951 | Blizzards happen across the middle latitudes and toward the poles, usually as part of a mid-latitude cyclone. Bliz- zards are most common in winter, when the jet stream has traveled south and a cold, northern air mass comes into contact with a warmer, semitropical air mass (Figure 1.2). The very strong winds develop because of the pressure gradient between the low-pressure storm and the higher pressure west of the storm. Snow produced by the storm gets caught in the winds and blows nearly horizontally. Blizzards can also produce sleet or freezing rain. A blizzard obscures the Capitol in Wash- ington, DC. Blizzard snows blanket the East Coast of the United States in February 2010. | text | null |
L_0101 | blizzards | T_0952 | In winter, a continental polar air mass travels down from Canada. As the frigid air travels across one of the Great Lakes, it warms and absorbs moisture. When the air mass reaches the leeward side of the lake, it is very unstable and it drops tremendous amounts of snow. This lake-effect snow falls on the snowiest metropolitan areas in the United States: Buffalo and Rochester, New York (Figure 1.3). Click image to the left or use the URL below. URL: Frigid air travels across the Great Lakes and dumps lake-effect snow on the lee- ward side. | text | null |
L_0102 | branches of earth science | T_0953 | Geology is the study of the Earths solid material and structures and the processes that create them. Some ideas geologists might consider include how rocks and landforms are created or the composition of rocks, minerals, or various landforms. Geologists consider how natural processes create and destroy materials on Earth, and how humans can use Earth materials as resources, among other topics. Geologists study rocks in the field to learn what they can from them. | text | null |
L_0102 | branches of earth science | T_0954 | Oceanography is the study of everything in the ocean environment, which covers about 70% of the Earths surface. Recent technology has allowed people and probes to venture to the deepest parts of the ocean, but much of the ocean remains unexplored. Marine geologists learn about the rocks and geologic processes of the ocean basins. | text | null |
L_0102 | branches of earth science | T_0955 | Meteorology includes the study of weather patterns, clouds, hurricanes, and tornadoes. Using modern technology such as radars and satellites, meteorologists are getting more accurate at forecasting the weather all the time. Climatology is the study of the whole atmosphere, taking a long-range view. Climatologists can help us better understand how and why climate changes (Figure 1.2). Carbon dioxide released into the atmo- sphere is causing the global climate to change. | text | null |
L_0102 | branches of earth science | T_0956 | Environmental scientists study the effects people have on their environment, including the landscape, atmosphere, water, and living things. Climate change is part of climatology or environmental science. | text | null |
L_0102 | branches of earth science | T_0957 | Astronomy is the study of outer space and the physical bodies beyond the Earth. Astronomers use telescopes to see things far beyond what the human eye can see. Astronomers help to design spacecraft that travel into space and send back information about faraway places or satellites (Figure 1.3). The Hubble Space Telescope. Click image to the left or use the URL below. URL: Click image to the left or use the URL below. URL: | text | null |
L_0115 | collecting weather data | T_1018 | To make a weather forecast, the conditions of the atmosphere must be known for that location and for the surrounding area. Temperature, air pressure, and other characteristics of the atmosphere must be measured and the data collected. | text | null |
L_0115 | collecting weather data | T_1019 | Thermometers measure temperature. In an old-style mercury thermometer, mercury is placed in a long, very narrow tube with a bulb. Because mercury is temperature sensitive, it expands when temperatures are high and contracts when they are low. A scale on the outside of the thermometer matches up with the air temperature. Some modern thermometers use a coiled strip composed of two kinds of metal, each of which conducts heat differently. As the temperature rises and falls, the coil unfolds or curls up tighter. Other modern thermometers measure infrared radiation or electrical resistance. Modern thermometers usually produce digital data that can be fed directly into a computer. | text | null |
L_0115 | collecting weather data | T_1020 | Meteorologists use barometers to measure air pressure. A barometer may contain water, air, or mercury, but like thermometers, barometers are now mostly digital. A change in barometric pressure indicates that a change in weather is coming. If air pressure rises, a high pressure cell is on the way and clear skies can be expected. If pressure falls, a low pressure cell is coming and will likely bring storm clouds. Barometric pressure data over a larger area can be used to identify pressure systems, fronts, and other weather systems. | text | null |
L_0115 | collecting weather data | T_1021 | Weather stations contain some type of thermometer and barometer. Other instruments measure different characteris- tics of the atmosphere, such as wind speed, wind direction, humidity, and amount of precipitation. These instruments are placed in various locations so that they can check the atmospheric characteristics of that location (Figure 1.1). Weather stations are located on land, the surface of the sea, and in orbit all around the world. According to the World Meteorological Organization, weather information is collected from 15 satellites, 100 stationary buoys, 600 drifting buoys, 3,000 aircraft, 7,300 ships, and some 10,000 land-based stations. | text | null |
L_0115 | collecting weather data | T_1022 | Radiosondes measure atmospheric characteristics, such as temperature, pressure, and humidity as they move through the air. Radiosondes in flight can be tracked to obtain wind speed and direction. Radiosondes use a radio to communicate the data they collect to a computer. Radiosondes are launched from about 800 sites around the globe twice daily to provide a profile of the atmosphere. Radiosondes can be dropped from a balloon or airplane to make measurements as they fall. This is done to monitor storms, for example, since they are dangerous places for airplanes to fly. | text | null |
L_0115 | collecting weather data | T_1023 | Radar stands for Radio Detection and Ranging (Figure 1.2). A transmitter sends out radio waves that bounce off the nearest object and then return to a receiver. Weather radar can sense many characteristics of precipitation: its location, motion, intensity, and the likelihood of future precipitation. Doppler radar can also track how fast the precipitation falls. Radar can outline the structure of a storm and can be used to estimate its possible effects. Radar view of a line of thunderstorms. | text | null |
L_0115 | collecting weather data | T_1024 | Weather satellites have been increasingly important sources of weather data since the first one was launched in 1952. Weather satellites are the best way to monitor large-scale systems, such as storms. Satellites are able to record long-term changes, such as the amount of ice cover over the Arctic Ocean in September each year. Weather satellites may observe all energy from all wavelengths in the electromagnetic spectrum. Visible light images record storms, clouds, fires, and smog. Infrared images record clouds, water and land temperatures, and features of the ocean, such as ocean currents (Figure 1.3). Click image to the left or use the URL below. URL: Infrared data superimposed on a satellite image shows rainfall patterns in Hurricane Ernesto in 2006. | text | null |
L_0126 | development of theories | T_1052 | Scientists seek evidence that supports or refutes a hypothesis. If there is no significant evidence to refute the hypothesis and there is an enormous amount of evidence to support it, the idea is accepted. It may become a theory. A scientific theory is strongly supported by many different lines of evidence. A theory has no major inconsistencies. A theory must be constantly tested and revised. A theory provides a model of reality that is simpler than the phenomenon itself. Scientists can use a theory to offer reliable explanations and make accurate predictions. A theory can be revised or thrown out if conflicting data is discovered. However, a longstanding theory that has lots of evidence to back it up is less likely to be overthrown than a newer theory. But science does not prove anything beyond a shadow of a doubt. Click image to the left or use the URL below. URL: | text | null |
L_0126 | development of theories | T_1053 | Many people think that any idea that is completely accepted in science is a law. In science, a law is something that always applies under the same conditions. If you hold something above the ground and let go it will fall. This phenomenon is recognized by the law of gravity. A law explains a simpler phenomenon or set of phenomena than does a theory. But a theory tells you why something happens and a law only tells you that it happens. Amazingly, scientific laws may have exceptions. Even the law of gravity does not always hold! If water is in an enclosed space between a hillside and a glacier, the weight of the glacier at the bottom of the hill may force the water to flow uphill - against gravity! That doesnt mean that gravity is not a law. A law always applies under the right circumstances. Click image to the left or use the URL below. URL: | text | null |
L_0149 | effect of continental position on climate | T_1125 | When a particular location is near an ocean or large lake, the body of water plays an extremely important role in affecting the regions climate. A maritime climate is strongly influenced by the nearby sea. Temperatures vary a relatively small amount seasonally and daily. For a location to have a true maritime climate, the winds must most frequently come off the sea. A continental climate is more extreme, with greater temperature differences between day and night and between summer and winter. The oceans influence in moderating climate can be seen in the following temperature comparisons. Each of these cities is located at 37o N latitude, within the westerly winds (Figure 1.1). The climate of San Francisco is influenced by the cool California current and offshore upwelling. Wichita has a more extreme continental climate. Virginia Beach, though, is near the Atlantic Ocean. Why is the climate there less influenced by the ocean than is the climate in San Francisco? Hint: Think about the direction the winds are going at that latitude. The weather in San Francisco comes from over the Pacific Ocean while much of the weather in Virginia comes from the continent. How does the ocean influence the climate of these three cities? | text | null |
L_0149 | effect of continental position on climate | T_1126 | The temperature of the water offshore influences the temperature of a coastal location, particularly if the winds come off the sea. The cool waters of the California Current bring cooler temperatures to the California coastal region. Coastal upwelling also brings cold, deep water up to the ocean surface off of California, which contributes to the cool coastal temperatures. Further north, in southern Alaska, the upwelling actually raises the temperature of the surrounding land because the ocean water is much warmer than the land. The important effect of the Gulf Stream on the climate of northern Europe is described in the chapter Water on Earth. | text | null |
L_0152 | effects of air pollution on the environment | T_1132 | All air pollutants cause some damage to living creatures and the environment. Different types of pollutants cause different types of harm. | text | null |
L_0152 | effects of air pollution on the environment | T_1133 | Particulates reduce visibility. In the western United States, people can now ordinarily see only about 100 to 150 kilometers (60 to 90 miles), which is one-half to two-thirds the natural (pre-pollution) range on a clear day. In the East, people can only see about 40 to 60 kilometers (25-35 miles), about one-fifth the distance they could see without any air pollution (Figure 1.1). Particulates reduce the amount of sunshine that reaches the ground, which may reduce photosynthesis. Since particulates form the nucleus for raindrops, snowflakes, or other forms of precipitation, precipitation may increase Smog in New York City. when particulates are high. An increase in particles in the air seems to increase the number of raindrops, but often decreases their size. By reducing sunshine, particulates can also alter air temperature as mentioned above. Imagine how much all of the sources of particulates combine to reduce temperatures. What affect might this have on global warming? | text | null |
L_0152 | effects of air pollution on the environment | T_1134 | Ozone damages some plants. Since ozone effects accumulate, plants that live a long time show the most damage. Some species of trees appear to be the most susceptible. If a forest contains ozone-sensitive trees, they may die out and be replaced by species that are not as easily harmed. This can change an entire ecosystem, because animals and plants may not be able to survive without the habitats created by the native trees. Some crop plants show ozone damage (Figure 1.2). When exposed to ozone, spinach leaves become spotted. Soybeans and other crops have reduced productivity. In developing nations, where getting every last bit of food energy out of the agricultural system is critical, any loss is keenly felt. | text | null |
L_0152 | effects of air pollution on the environment | T_1135 | Oxide air pollutants also damage the environment. NO2 is a toxic, orange-brown colored gas that gives air a distinctive orange color and an unpleasant odor. Nitrogen and sulfur-oxides in the atmosphere create acids that fall as acid rain. Lichen get a lot of their nutrients from the air so they may be good indicators of changes in the atmosphere such as increased nitrogen. In Yosemite National Park, this could change the ecosystem of the region and lead to fires and other problems. The spots on this leaf are caused by ozone damage. Click image to the left or use the URL below. URL: | text | null |
L_0160 | evolution plate tectonics and climate change | T_1154 | Scientific theories are sometimes thrown out when the data shows them to be wrong. Before plate tectonics theory was accepted, people thought that fossil organisms had spread around using land bridges. Although a land bridge across the Atlantic seemed a bit far-fetched, there was no better idea. Most scientists were relieved when they could toss that theory out. But some theories account for so many phenomena and are so broadly supported by so many lines of evidence that they are unlikely ever to be disproved. Additional scientific evidence may reveal problems and scientists may need to modify the theories. But there is so much evidence to support them and nothing major to refute them that they have become essential to their fields of science. | text | null |
L_0160 | evolution plate tectonics and climate change | T_1155 | Darwins theory of evolution has been under attack ever since Darwin proposed it. But nearly all biologists accept the theory and recognize that everything they learn about life on Earth supports the theory. Evolution is seen in the fossil record, in the developmental paths of organisms, in the geographic distribution of organisms, and in the genetic codes of living organisms. Evolution has a mechanism, called natural selection. People often refer to natural selection as the survival of the fittest. With natural selection, the organism that is best adapted to its environment will be most likely to survive and produce offspring, thus spreading its genes to the next generation. The theory of evolution maintains that modern humans evolved from ape-like ancestors. | text | null |
L_0160 | evolution plate tectonics and climate change | T_1156 | The theory of plate tectonics is the most important theory in much of earth science. Plate tectonics explains why much geological activity happens where it does, why many natural resources are found where they are, and can be used to determine what was happening long ago in Earths history. The theory of plate tectonics will be explored in detail in later concepts. | text | null |
L_0160 | evolution plate tectonics and climate change | T_1157 | The theory of climate change is a much newer theory than the previous two. We know that average global tempera- tures are rising. We even know why: Carbon dioxide is released into the atmosphere when fossil fuels are burned. Carbon dioxide is a greenhouse gas. In the atmosphere, greenhouse gases trap heat. This is like putting an extra blanket over Earth. Since more heat is being trapped, global temperature is rising. There is very little information that contradicts the theory that climate is changing due in large part to human activities. Unless some major discrepancy is discovered about how the atmosphere works, the theory is very likely to stand. So far, the evidence that is being collected supports the idea and global warming can be used to predict future events, which are already taking place. This idea will be explored in detail in later concepts. | text | null |
L_0164 | extinction and radiation of life | T_1167 | Most of the species that have lived have also gone extinct. There are two ways to go extinct: besides the obvious way of dying out completely, a species goes extinct if it evolves into a different species. Extinction is a normal part of Earths history. But sometimes large numbers of species go extinct in a short amount of time. This is a mass extinction. The causes of different mass extinctions are different: collisions with comets or asteroids, massive volcanic eruptions, or rapidly changing climate are all possible causes of some of these disasters (Figure 1.1). | text | null |
L_0164 | extinction and radiation of life | T_1168 | After a mass extinction, many habitats are no longer inhabited by organisms because they have gone extinct. With new habitats available, some species will adapt to the new environments. Evolutionary processes act rapidly during An extinct Tyrannosaurus rex. This fossil resembles a living organism. these times and many new species evolve to fill those available habitats. The process in which many new species evolve in a short period of time to fill available niches is called adaptive radiation. At the end of this period of rapid evolution the life forms do not look much like the ones that were around before the mass extinction. For example, after the extinction of the dinosaurs, mammals underwent adaptive radiation and became the dominant life form. | text | null |
L_0168 | flow of matter in ecosystems | T_1184 | The flow of matter in an ecosystem is not like energy flow. Matter enters an ecosystem at any level and leaves at any level. Matter cycles freely between trophic levels and between the ecosystem and the physical environment (Figure | text | null |
L_0168 | flow of matter in ecosystems | T_1185 | Nutrients are ions that are crucial to the growth of living organisms. Nutrients such as nitrogen and phosphorous are important for plant cell growth. Animals use silica and calcium to build shells and skeletons. Cells need nitrates and phosphates to create proteins and other biochemicals. From nutrients, organisms make tissues and complex molecules such as carbohydrates, lipids, proteins, and nucleic acids. What are the sources of nutrients in an ecosystem? Rocks and minerals break down to release nutrients. Some enter the soil and are taken up by plants. Nutrients can be brought in from other regions, carried by wind or water. When one organism eats another organism, it receives all of its nutrients. Nutrients can also cycle out of an ecosystem. Decaying leaves may be transported out of an ecosystem by a stream. Wind or water carries nutrients out of an ecosystem. Nutrients cycle through ocean food webs. Decomposers play a key role in making nutrients available to organisms. Decomposers break down dead organisms into nutrients and carbon dioxide, which they respire into the air. If dead tissue would remain as it is, eventually nutrients would run out. Without decomposers, life on Earth would have died out long ago. | text | null |
L_0182 | global wind belts | T_1233 | Global winds blow in belts encircling the planet. Notice that the locations of these wind belts correlate with the atmospheric circulation cells. Air blowing at the base of the circulation cells, from high pressure to low pressure, creates the global wind belts. The global wind belts are enormous and the winds are relatively steady (Figure 1.1). | text | null |
L_0182 | global wind belts | T_1234 | Lets look at the global wind belts in the Northern Hemisphere. In the Hadley cell air should move north to south, but it is deflected to the right by Coriolis. So the air blows from northeast to the southwest. This belt is the trade winds, so called because at the time of sailing ships they were good for trade. In the Ferrel cell air should move south to north, but the winds actually blow from the southwest. This belt is the westerly winds or westerlies. In the Polar cell, the winds travel from the northeast and are called the polar easterlies. The wind belts are named for the directions from which the winds come. The westerly winds, for example, blow from west to east. These names hold for the winds in the wind belts of the Southern Hemisphere as well. Click image to the left or use the URL below. URL: | text | null |
L_0182 | global wind belts | T_1235 | The high and low pressure areas created by the six atmospheric circulation cells also determine in a general way the amount of precipitation a region receives. Rain is common in low pressure regions due to rising air. Air sinking in high pressure areas causes evaporation; these regions are usually dry. These features have a great deal of influence on climate. | text | null |
L_0182 | global wind belts | T_1236 | The polar front is the junction between the Ferrell and Polar cells. At this low pressure zone, relatively warm, moist air of the Ferrell Cell runs into relatively cold, dry air of the Polar cell. The weather where these two meet is extremely variable, typical of much of North America and Europe. | text | null |
L_0182 | global wind belts | T_1237 | The polar jet stream is found high up in the atmosphere where the two cells come together. A jet stream is a fast- flowing river of air at the boundary between the troposphere and the stratosphere. Jet streams form where there is a large temperature difference between two air masses. This explains why the polar jet stream is the worlds most powerful (Figure 1.2). A cross section of the atmosphere with major circulation cells and jet streams. The polar jet stream is the site of extremely turbulent weather. Jet streams move seasonally just as the angle of the Sun in the sky moves north and south. The polar jet stream, known as the jet stream, moves south in the winter and north in the summer between about 30 N and 50 to 75 N. Click image to the left or use the URL below. URL: | text | null |
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