4 Forecasting Weather

Transcription

1 CHAPTER 2 4 Forecasting Weather SECTION Understanding Weather BEFORE YOU READ After you read this section, you should be able to answer these questions: What instruments are used to forecast weather? How do you read a weather map? National Science Education Standards ES 1i, 1j What Is a Weather Forecast? Weather affects how you dress and how you plan your day. Severe weather can put people in danger. Therefore, accurate weather forecasts are important. A weather forecast is a prediction of weather conditions over the next few days. Meteorologists make weather forecasts using information on atmospheric conditions. Meteorologists use special instruments to collect data. Some of these instruments are far above the ground. Others are tools you may be familiar with from everyday use. WEATHER BALLOONS Weather balloons carry electronic equipment. The equipment on a weather balloon can measure weather conditions as high as 30 km above Earth s surface. This equipment measures temperature, air pressure, and relative humidity. It transmits the information to meteorologists using radio signals. Meteorologists can track the path of the balloons to measure wind speed and direction. STUDY TIP Compare As you read this section, make a chart comparing the different tools that meteorologists use to collect weather data. 1. Explain What do meteorologists use to forecast the weather? 2. Describe How do meteorologists obtain the information from weather balloons? Weather balloons carry equipment into the atmosphere. They use radio signals to transmit information on weather conditions to meteorologists on the ground. Interactive Textbook 43 Understanding Weather

2 SECTION 4 Forecasting Weather continued THERMOMETERS AND BAROMETERS Remember that air temperature and pressure can affect the weather. Therefore, meteorologists must be able to measure temperature and pressure accurately. They use thermometers to measure temperature, just like you do. They use tools called barometers to measure air pressure. Critical Thinking 3. Infer Why is it important for meteorologists to be able to measure wind direction? WINDSOCKS, WIND VANES, AND ANEMOMETERS Meteorologists can use windsocks and wind vanes to measure wind direction. A windsock is a cone-shaped cloth bag that is open at both ends. The wind enters through the wide end and leaves through the narrow end. The wide end always points into the wind. A wind vane is shaped like an arrow. It is attached to a pole. The wind pushes the tail of the arrow. The vane spins until the arrows points into the wind. An anemometer measures wind speed. It has three or four cups connected to a pole with spokes. The wind pushes on the open sides of the cups. This makes them spin on the pole. The spinning of the pole produces an electric current, which is displayed on a dial. The faster the wind speed, the stronger the electric current, and the further the dial moves. 4. Identify What is an anemometer? Meteorologists use anemometers to measure wind speed. 5. Describe Give two things that meteorologists can use radar to do. RADAR AND SATELLITES Scientists use radar to locate fronts and air masses. Radar can locate a weather system and show the direction it is moving. It can show how much precipitation is falling, and what kind of precipitation it is. Most television stations use radar to give information about weather systems. Weather satellites orbiting Earth produce images of weather systems. Satellites can also measure wind speeds, humidity, and temperatures from different altitudes. Meteorologists use weather satellites to track storms. Interactive Textbook 44 Understanding Weather

3 SECTION 4 Forecasting Weather continued What Are Weather Maps? In the United States, two main groups of scientists collect weather data. One group is the National Weather Service (NWS). The other group is the National Oceanic and Atmospheric Administration (NOAA). These groups gather information from about 1,000 weather stations across the United States to produce weather maps. READING A WEATHER MAP Some weather maps contain station models. A station model is a symbol that shows the weather at a certain location. Station models look like circles with numbers and symbols around them. The numbers and symbols stand for different measurements, as shown below. 6. Identify What are two groups that collect weather data in the United States? 7. Use a Model What is the dew point temperature for the station shown in the figure? 8. Infer Will condensation happen in the air at the station in the figure? Explain your answer. Some weather maps, such as those you see on television, show lines called isobars. Isobars are lines that connect points of equal air pressure. They are similar to contour lines on a topographic map. Isobars that form closed circles represent areas of high (H) or low (L) pressure. Weather maps also show fronts. 9. Read a Map On the map, circle the areas of high pressure. Interactive Textbook 45 Understanding Weather

4 Section 4 SECTION VOCABULARY anemometer an instrument used to measure wind speed barometer an instrument that measures atmospheric pressure NSES ES 1i, 1j thermometer an instrument that measures and indicates temperature 1. Compare How is an anemometer different from a windsock or a wind vane? 2. Identify What three atmospheric conditions do weather balloons measure? 3. Describe Give three things that meteorologists use weather satellites for. 4. Apply Concepts Which of the two weather stations below is experiencing higher air temperatures? Which is experiencing higher wind speeds? 5. Apply Concepts In which direction is the wind blowing at station A? In which direction is it blowing at station B? Interactive Textbook 46 Understanding Weather

5 I Weather and Climate Answer Key continued 1. A front is a place where two air masses meet. 2. First row, from left to right: rises and cools; cloudy, rainy, and stormy Second row, from left to right:... higher than surrounding pressure; dry and clear 3. cold, warm, occluded, stationary 4. Pacific Ocean, Atlantic Ocean, Gulf of Mexico 5. ct SECTION 3 SEVERE WEATHER 1. It must contain enough water vapor to form clouds. 2. Electricity travels between an area with a positive charge and an area with a negative charge. 3. sound produced by vibrations in expanding air that was superheated by lightning 4. The center of the tornado has low pressure. 5. when it touches the ground mph to 112 mph 7. Ocean water is too cold there. 8. the Coriolis effect 9. the center of the hurricane that contains warm, fairly calm air with low pressure 10. a rise in sea level because of a storm 11. to learn where the storm is and whether it is getting worse 1. Lightning superheats the air to produce thunder. 2. They can produce strong winds, tornadoes, hail, or flash floods. 3. in the United States 4. Cold, dry air from Canada meets warm, moist air from the Tropics, producing thunderstorms. 5. Solar energy causes water to evaporate. As it rises, cools, and condenses, it releases the energy. Thunderstorms form, which can combine to form hurricanes. 6. when they move over cooler water or land 7. If you are outside, stay away from tall objects that can attract lightning. If you are in the open, crouch down. Stay away from water. SECTION 4 FORECASTING THE WEATHER 1. information on atmospheric conditions 2. The balloons transmit the data using radio signals. 3. Possible answer: Wind direction can indicate which way a weather system is moving. 4. a device that measures wind speed 5. Locate weather systems; determine how much precipitation is being produced. 6. NWS, NOAA F 8. No, because the air temperature is above the dew point (temperature). 9. The three Hs on the map should be circled. 1. An anemometer measures wind speed; windsocks and wind vanes measure only wind direction. 2. temperature, pressure, relative humidity 3. tracking storms, imaging weather systems, measuring wind speed/humidity/temperature from different altitudes 4. Station A has higher air temperatures and higher wind speeds. 5. Station A: southwest Station B: north Chapter 3 Climate SECTION 1 WHAT IS CLIMATE? 1. temperature and precipitation 2. The sun s energy is focused on a small area. 3. The equator receives about the same amount of sunlight all year round. 4. differences in air pressure 5. west to east 6. Temperature decreases as elevation increases. 7. The air cools as it rises and drops below its dew point. 8. Water absorbs and releases heat more slowly than land, so the water helps to stabilize the temperatures on land. 9. The cool water absorbs heat from the air, causing the temperature of the air to decrease. 10. a warm current 11. latitude 12. tropical zone 13. The climate of an area affects the organisms that live there. 14. along the equator Interactive Textbook Answer Key 58 Weather and Climate