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Tropical Cyclones Unit 2 – the Life of a Cyclone

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Tropical Cyclones Unit 2 – the Life of a Cyclone Data Detectives: Tropical Cyclones Unit 2 – The Life of a Cyclone Unit 2 The Life of a Cyclone In this unit, you will learn • What are the stages in the life of a tropical cyclone? • How, where, and why do tropical cyclones die? • How do scientists track tropical storms? • How do you determine the intensity of a tropical storm? NASA/GSFC Three satellite images superimposed on the same map show the development of Hurricane Georges on September 25, 1998. 33 Data Detectives: Tropical Cyclones Unit 2 – The Life of a Cyclone 34 Data Detectives: Tropical Cyclones Unit 2 – The Life of a Cyclone Warm-up 2.1 Observing tropical cyclones Th e 1900 Galveston Hurricane was the worst natural disaster in U.S. history. Why was this hurricane so destructive? Part of the answer is that, in 1900, forecasters had to make predictions based almost exclusively on direct observation. Th e skies, the tides, and the changing winds and air pressure were their only clues that a hurricane was coming. Unfortunately, by the time they realized it, the storm was nearly upon them. Th e forecasters had little time to warn the residents to evacuate or to seek shelter. Today’s forecasters use sophisticated tools to locate and track tropical cyclones well before they make landfall. By modeling tropical cyclones Media Viewer web site on computers, researchers are improving their ability to accurately If you have any view of the predict storm tracks. Using satellites and other modern tools, forecasters cyclones.apr project open in observe and measure cyclones remotely. To learn about both direct ArcView, you can click the Media and indirect methods of observing tropical cyclones, point your Web Viewer button and choose browser to the following NOAA Web site: Observing Tropical Cyclones from the media list to open this hurricanes.noaa.gov/prepare/observation.htm web page in your browser. On the NOAA Web page, click on each of the technologies to learn Who or what is NOAA? more about it. Find out how each tool helps scientists monitor these dangerous storms. In Table 1, list the name of each technology and tell NOAA is the National Oceanic and Atmospheric Administration. whether it provides a direct or an indirect method of observation. It is a government agency NOAA that conducts research and gathers data about the oceans, 3 atmosphere, space, and sun. 1 2 NOAA warns of dangerous weather, charts our seas and skies, guides our use and protection of ocean and coastal resources, and conducts research to improve our 5 6 understanding and stewardship of the environment. 4 Part of the U.S. Department of Commerce, NOAA provides Table 1 — Modern weather-observation technologies services through fi ve major organizations. Number Name of technology Direct or Indirect? • National Weather Service 1 • National Ocean Service • National Marine Fisheries 2 Service 3 • National Environmental 4 Satellite, Data and Information Service 5 • NOAA Research and special 6 program units Observing tropical cyclones 35 Data Detectives: Tropical Cyclones Unit 2 – The Life of a Cyclone 1. What are the two main types of satellite imagery used in tropical cyclone forecasting? 2. Radiosondes and dropsondes help us understand the structure of tropical cyclones by measuring and transmitting information about which atmospheric properties? 3. What is the most direct method of measuring the wind speeds within a tropical cyclone? 4. Which two important properties of tropical cyclones are measured using radar? 36 Observing tropical cyclones Data Detectives: Tropical Cyclones Unit 2 – The Life of a Cyclone Investigation 2.2 Tracking Hurricane Georges Tropical cyclones do not start out fully developed. Like people, who grow from infant to child to adult, tropical cyclones also experience stages of growth. Unfortunately, instead of “mellowing out,” hurricanes get nastier and generally more dangerous with age. Th is investigation explores the development of a single hurricane, Georges (pronounced zhorzh), that aff ected Atlantic and Caribbean coastal communities in September 1998. Launch ArcView, locate and open the cyclones.apr fi le, and open the Tracking Georges view. Th is view shows the path, or track, of Hurricane Georges as it swept across the Atlantic and the Caribbean. Hurricane Georges was the 19th most deadly tropical cyclone in history. Th e large number of casualties occurred as Georges passed directly over several Caribbean islands. An eye in the sky Th is view’s table of contents contains seven themes, labeled by date and time, that show satellite images of Hurricane Georges at diff erent points along its journey across the Atlantic Ocean. To turn a theme on or off , click its Begin with the 9/15 10:19 UT theme, then turn on each of the checkbox in the Table of Contents. seven hurricane image themes in order by date. Th e hurricane’s clouds were not bright colors like those you see on your screen (Figure 1). Th ese false colors show the temperatures of the cloud tops recorded by the satellite’s infrared sensor. Grays and whites represent the warmest temperatures, whereas greens, yellows, and reds show the coldest (Figure 2). Temperature decreases with Higher cloud tops = Cooler temperatures = Stronger convection red NOAA orange yellow Lower cloudtops = green Warmer temperatures = Weaker convection blue violet Increasing altitude white Decreasing temperature Decreasing gray black Figure 1. False-color image of Hurricane Georges. The highest (coldest) cloudtops shown in orange and yellow, indicate where Figure 2. Relationship between color, cloud temperature, and height upward convection is strongest. in false-color satellite images. Tracking Hurricane Georges 37 Data Detectives: Tropical Cyclones Unit 2 – The Life of a Cyclone Universal Time (UT) altitude, so colder temperatures indicate higher cloud tops. As the The times listed in the Hurricane upward convection in a storm intensifi es, clouds rise higher into the Georges IR Images layer group atmosphere. Th us, the cloud temperatures tell us about the strength of are in 24-hour Universal Time the convection, which in turn indicates the energy of the hurricane. format. Abbreviated UT, this is the time at 0° longitude, or the prime 1. On what date did Hurricane Georges make landfall on the U.S. meridian. mainland? How many days did it take Hurricane Georges to travel The U.S. Atlantic Coast is 5 time across the Atlantic Ocean before landfall? zones west of the prime meridian. Subtract 5 hours from Universal Time to get local time for the Atlantic Coast. 2. Convert the number of days from question 1 into hours. 3. In what direction did Georges travel as it crossed the ocean? Now you will measure the total distance Georges traveled and use it to fi nd the average rate of travel, or speed of the storm. Using the Measure tool , click on the September 15 storm center. Drag the measuring tool through each of the fi ve storm centers. Double-click on the last storm center (September 27) to fi nish the measurement. Th e total distance Georges traveled (Length) is reported in the status bar. Read distance here (your distance will be different). 4. How far (in km) did Georges travel? 5. Use this distance and the number of hours you calculated in question 2 to fi nd Georges’ average speed (in km/hr) as it crossed the Atlantic Ocean (speed = distance ÷ time). 38 Tracking Hurricane Georges Data Detectives: Tropical Cyclones Unit 2 – The Life of a Cyclone 6. An average person walks at a speed of about 6.5 km/hr, and runs at about 10 km/hr. Compare these rates with the average speed you calculated for Hurricane Georges. 7. If a major tropical cyclone is spotted 500 km off shore, how much warning time might a coastal community have before the storm strikes? (time = distance ÷ speed) On the path of a killer Next you will learn about the countries aff ected by Georges as it traveled across the Atlantic. Look at the Storm Track theme, which shows the path of the center of the hurricane as it crossed the Atlantic Ocean. Turn the Georges images on and off as needed to better see the track. Activate the Countries theme. Using the Identify tool , click on a country or island and read To activate a theme, click on its name in the Table of Contents. the Name of the country in the Identify Results window. If you need to identify U.S. states, activate the States theme before using the Identify tool . 8. Identify these landmarks associated with Hurricane Georges as it crossed the Atlantic Ocean: a. Hurricane Georges formed south of this group of islands off the west coast of Africa: _______________________. b. Georges passed directly over three large Caribbean island countries and one U.S. territory. Th ese are ________________, ______________, _____________, and _______________. c. Th e fi rst U.S. state aff ected by Georges’ heavy rainfall and strong winds was _________________. d. Th e U.S. state where the eye of Hurricane Georges fi rst made landfall was ____________________. Hurricane formation Click the QuickLoad button , select the Formation and Movement view, and click OK. Turn on the Formation Points theme. Tracking Hurricane Georges 39 Data Detectives: Tropical Cyclones Unit 2 – The Life of a Cyclone Each point in this theme indicates where a storm system fi rst showed the typical features of a tropical cyclone in the Atlantic between 1950 – 2005. Notice that the points are not evenly distributed. 9. On Map 1, identify and label two areas where hurricane formation in the Atlantic appears to be concentrated. Map 1 — North Atlantic Ocean hurricane-formation regions Turn on the End Points theme. Look for areas where hurricanes appear to lose strength and die.
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