Briana Ryan 11/20/06 Green Honors Chapter 17 Objectives 1. Identify the major types of air masses that affect the weather in North America. These four major types of air masses affect the weather for North America. Maritime Tropical is warm, humid air that forms over oceans near the tropics. They form over the Gulf of Mexico and the Pacific Ocean, these air masses of maritime tropical move first into the Southeastern United States. Then the air masses move North and Northeast, where they affect the weather in central and eastern United States. In the west, Maritime Tropical air masses form over the Pacific Ocean. These affect the weather on the west coast. The Pacific air masses lose moisture. They bring dry air to the eastern slopes. In summer, maritime tropical air masses bring hot, humid weather. In winter, a humid air mass can bring heavy rain or snow. Maritime Polar is cool, humid air that forms over the icy cold North Pacific and North Atlantic oceans. These air masses affect the West coast more than the East coast. In summer, these masses of cool, humid air often bring fog, rain, and cool temperatures to the West coast. Continental Tropical is hot, dry air masses that form only in summer over dry areas of the Southwest and northern Mexico. These air masses cover a smaller area than other air masses. They occasionally move northeast, bringing hot, dry weather to the southern Great Plains. Continental Polar is cool, or cold air that moves over central and northern Canada and Alaska. In winter, these air masses bring clear, cold, dry air to much of North America. The air masses that can bring bitterly, cold weather with very low humidity forms near the Arctic Circle. In summer, storms can occur when continental polar air masses move south and meet maritime tropical air masses moving north. These paragraphs show how the weather can be affected in North America. 2. Name and describe the main types of fronts. The following are the main types of fronts. Cold Fronts form when cold air moves underneath warm air, forcing the warm air to rise. A rapidly moving cold air mass runs through a slowly moving warm air mass, then the denser cold air slides right underneath the lighter warm air, pushing it upwards. Cold fronts can bring violent thunderstorms. Warm Fronts form when warm air moves over cold air. Clouds, rain, and storms come with this. Cold air is denser than warm air, so the warm air moves over the cold air. If the warm air is humid, showers and light rain fall along the front, where the warm and cold air meet. If it’s dry, scattered clouds form. In winter, warm fronts bring snow. Because warm fronts are slow, they can bring rain or fog for many days. Stationary Fronts are when cold and warm air masses meet, neither one has enough force to move the other. The two air masses have a “stand off”. When the two meet, water vapor in the warm air condenses into rain, fog, snow, or clouds. Stationary fronts can remain stalled for a couple of days, bringing many days of clouds and precipitation. Occluded Fronts are when a cold air mass and a cool air mass come together, the warm air caught between them is forced upward. The temperature near the ground becomes cooler. The warm air is cut off or occluded, from the ground. As the warm air-cools and it’s water vapor condenses, the weather may turn cloudy and rainy or snowy. These fronts are important for the weather and air. 3. Define cyclones and anticyclones. Cyclones and anticyclones are important for knowing high and low pressure. A cyclone is a swirling center of low pressure. Cyclones have been shown on the weather map by the letter, “L”. Anticyclones are opposite on pressure wise. They have high-pressure centers of dry air. They have been shown on a weather map by the letter, “H”. These are what cyclones and anticyclones are. 4. List the main kinds of storms and explain how they form. The main kinds of storms are thunderstorms, tornadoes, hurricanes, and winter storms. Thunderstorms form by large cumulonimbus clouds, or thunderheads. Mostly the reason why these clouds form is because warm air is forced upward at a cold front. Cumulonimbus clouds also form on hot, humid afternoons in the spring and summer. The warm, humid air rises rapidly. As the air rises, it cools, forming dense thunderheads. Heavy rains fall, sometimes along with hail. Tornadoes form in low, heavy cumulonimbus clouds, which are the same clouds that form thunderstorms. Tornadoes are most likely to occur in spring and early summer, usually late in the afternoon because the ground is warm. They can also be created when a warm, humid air mass moves north from the Gulf of Mexico into the lower Great Plains. A cold, dry air mass moves south from Canada. When the two masses meet, the warm air rises into the air as the cold air moves underneath it. Then a squall line of thunderstorms can happen, where storms travel from southwest to northeast. A single squall line can cause ten or more tornadoes. Hurricanes form over warm water as a low-pressure area, or tropical disturbance. The tropical disturbance grows in size and strength; it soon becomes a tropical storm, which could then later become a hurricane. A hurricane gets its energy from warm, humid air at the ocean’s surface. As this air rises and forms clouds, more air is put into the building of the hurricane. Winds spiral inward toward the areas of low pressure. Inside the storm are heavy rains and high winds. The lowest air pressure and warmest temperatures are at the center of the hurricane. The lower the air pressure at the center of a storm, the faster the winds blow toward the center. Winter storms form because snow falls when humid air cools below 0 degrees Celsius. Winds can pick up the snow from the ground, blowing it in different directions. Blowing snow makes it easier for people to get lost, so it’s dangerous. Also, the strong winds can cool a person’s body rapidly. These are the main types of storms. 5. Describe measures you can take to ensure safety during a storm. Some measures you can take to be safe during a storm are evacuating cars, hiding in basements, staying in safe parts of houses, and staying away from open spaces outside. For thunderstorms, you shouldn’t touch anything metal, go outside in open spaces or even go outside at all. Trees can be stricken by lightning because it’s usually a tall object outside. If you are outside though, you should crouch with your head down and your hands on your knees. For tornadoes, the best thing would be going into a basement of a well-built house. If the house doesn’t have a basement, you should move to the middle of the floor, away from windows and doors, because they could break and fly through the air. Lie on the floor under a sturdy piece of furniture. If you’re in a car or outside, you should move to a building or lie in a ditch flat. For hurricanes, you should be prepared to evacuate, or move away from your area temporarily. This should happen when you hear a “hurricane watch.” When you hear a “hurricane warning,” you should leave the area immediately. If you have to stay in a house, you should move to the interior of the building, away from windows. For winter storms, if you’re in a car, the driver can keep the engine running, but that’s only if the exhaust pipe is clear of snow. Finding shelter from wind from a snowstorm would be one of the best things, but before you go look for shelter, you should cover any exposed body parts with something to keep it dry. These are definitely some things to do when you’re caught in dangerous storms like these. 6. Identify the causes of flooding. A couple causes of flooding are too much rain, a lot of water in rivers and streams and flash floods, which can happen because rivers rise rapidly. When too much precipitation falls from the clouds, it can keep raining for several days, even from hurricanes and thunderstorms. Hurricanes can bring downpours of rain, which can flood the channels quickly. Unexpected floods, like flash floods, are the most dangerous because people don’t expect when they’re going to happen. So a giant flood can happen, within hours, or even minutes, of a storm. Melting snow can also bring a flood to the area. These are some of the causes of flooding. 7. Explain how the dangers of flooding can be reduced. The dangers of flooding can be reduced by advanced warnings. Scientists check weather satellites because they can supply information about snow so scientists can estimate how much water will run into rivers when the snow melts. Radar can track and measure the size of an approaching rainstorm. Scientists check river gauges that measure water levels. Forecasters can predict flood heights at different points along the river with all this information, which they can soon issue a warning to people early enough to get them to evacuate, which is an advanced warning. These examples show how advanced warnings can help flooding be reduced. 8. Explain how technology helps forecasters predict the weather. Technology helps forecasters predict the weather because computers and satellites can tell what weather is coming. Weather balloons and satellites measure temperature, air pressure, and humidity. Cameras on weather satellites can take pictures of Earth’s surface, clouds, storms, and ice and snow cover. These images are then transferred to meteorologists, who interpret the data. Computer forecasts can process large information quickly, which can help forecasters predict weather quickly. The computer starts with weather conditions, reported from weather stations around the area. The conditions include wind speed and direction, humidity, sunlight, temperature and air pressure. Then the computer makes thousands of calculations for 12 hours, 24 hours, 36 hours and so on. Each forecast builds on the previous forecast, so computers make forecaster’s and meteorologist’s jobs so much easier to predict the weather. These instruments help predict the weather pretty easily. 9. Describe the types of information shown on weather maps. The different types of information on weather maps are temperature, high and low pressure, isobars and isotherms, fronts, and precipitation. Isobars are lines joining places on the map that have the same air pressure. Isotherms are line-joining places that have the same temperature. The numbers on isobars are the pressure readings. The isotherm may be labeled with the temperature in Fahrenheit, degrees Celsius, or both. The colors on the weather maps can show areas with the same temperature. Precipitation can be shown in symbols that look like raindrops or snowflakes. The fronts also have symbols, either circular or pointed to show which direction either one is going. High and low pressure are shown with an “H” or an “L.” All of this information is shown on a weather map. 10. Describe El Nino and its effects. El Nino is a warm-water even change. El Nino occurs in the tropical Pacific Ocean. During this event, winds shift and push warm surface water toward the west coast of South America. The warm water replaces the cold water that usually rises from the deep ocean near the coast. El Nino happens every two to seven years. They can change climate significantly around the Pacific Ocean and other places. Scientists have looked for clues and warnings to help predict the return of El Nino. One signal is rising surface temperatures in the tropical part of the Pacific Ocean. Scientists were actually able to predict the results of the 1997-1998 El Nino events. In conclusion, El Nino can be important for people who live around the Pacific Ocean.