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I.2 Tropical cyclones
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I.2 Tropical cyclones

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  • 1. HAZARD #2: TROPICAL CYCLONES (HURRICANES, TYPHOONS, CYCLONES)Category 5 tropical cyclone “Isabel” (2003), North of the Caribbean islands, seen fromspace, with peak winds of 265 km/h (only ~ 50 victims)Tropical cyclone: storm system characterized by a large low-pressure center(depression) and numerous thunderstorms that produce very strong winds (100-300km/h) and heavy rain (500mm in 24hrs) and ocean surges (1-10 meters)
  • 2. TROPICAL CYCLONE CHARACTERISTICS: ATMOSPHERIC CIRCULATION The atmospheric circulation is the result of the Coriolis force due to the rotation of the planet Note: ICTZ = Inter-Tropical Convergence Zone1. Explain three factors required to lead to formation of cumulonimbus clouds2. Name two regions of the globe which combine these three factors
  • 3. TROPICAL CYCLONES CHARACTERISTICS: FORMATION OF A TROPICAL CYCLONE (DEPRESSION)1. Explain why tropical cyclones form in the ITCZ2. State the direction taken by upward spiraling winds in the Northern hemisphere, due to the Coriolis force3. Describe the difference between cumulo- nimbus and cirrus clouds4. Explain why tropical cyclones lose strength when passing over land Cirrus clouds Cumulo-nimbus clouds
  • 4. TROPICAL CYCLONES CHARACTERISTICS: EYE VS RAINBANDS
  • 5. TROPICAL CYCLONES CHARACTERISTICS: PRESSURE + WIND-DRIVEN WATER SURGE• Pressure surge is usually about 10mm for every millibar of pressure drop (normal is 1015 mb• Strong tropical depression can drop to ~900 mb (= 1 m pressure surge + wind-effect) Explain what causes huge surges during tropical cyclones Katrina surge (2005)
  • 6. TROPICAL CYCLONES: SPATIAL DISTRIBUTION 1. Circle regions which combine high hazard + high vulnerability 2. Suggest factors which explain the extensive damages caused by a tropical cyclone
  • 7. TROPICAL CYCLONE: DAMAGE FACTORS• Strength of tropical cyclone: not a factor in itself however, if the storm doesn’t make landfall or doesn’t hit a densely populated area (eg: almost not casualties during category 5 hurricane Frances, 2004)• Distribution of population: populations living in windward low-lying coastal areas are very vulnerable (e.g.: Cancun, Miami, New Orleans, some Caribbean Islands• Development level: planning laws, emergency planning, evacuation measures, relief operations, housing types, etc. MEDCs tend to have better preparedness and response to tropical cyclones than some very poor LEDCsCase-studies in textbook (p.206-207):• Hurricane Katrina (US Gulf Coast, 2005): 1,800 casualties + 800,000 homeless, winds up to 225 km/h, surge up to 9m• Cyclone Nargis (Burma, 2008): 134,000 casualties + millions homeless1. Research why Katrina caused extensive damages2. Explain why Nargis was more destructive than Katrina