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TORNADOES

TORNADOES. Small and intense cyclone in which air spirals at tremendous speed (250 mph or more) Associated with thunderstorms produced by fronts (North America) Also: inside hurricanes. ~ 1000 tornadoes across US reported per year Most common in spring and summer.

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TORNADOES

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  1. TORNADOES • Small and intense cyclone in which air spirals at tremendous speed (250 mph or more) • Associated with thunderstorms produced by fronts (North America) • Also: inside hurricanes • ~ 1000 tornadoes across US reported per year • Most common in spring and summer A dark funnel cloud hanging from base of cumulonimbus 100-450 m diameter

  2. WHAT ARE THE FAVORABLE CONDITIONS TO HAVE A TORNADO? • A cumulonimbus cloud traveling in advance of a cold front • Front of mP air (cold, moist) lifts warm, moist mT air

  3. Before thunderstorms develop: an invisible, horizontal spinning effect in the lower atmosphere. Rising air within the thunderstorm updraft: rotating air from horizontal to vertical An area of rotation, 2-6 miles wide, now extends through much of the storm. Most strong and violent tornadoes form within this area of strong rotation.

  4. More activity in central and southern states Less frequent: eastern coast Almost unknown: west of Rocky Mountains

  5. TROPICAL AND EQUATORIAL WEATHER SYSTEMS • Weak upper level winds • Air masses have similar characteristics (warm, moist) • Air masses move slowly • NO fronts and wave cyclones • Intense convectional activity TROPICAL CYCLONES Hurricane: western hemisphere Typhoon : Western Pacific Cyclone: Indian Ocean

  6. HURRICANES They originate as easterly waves or weak lows. They intensify and grow into a deep and circular low Winds greater than 74 mi/hr. They circulate: counterclockwise in Northern Hemisphere clockwise in Southern Hemisphere

  7. HOW ARE HURRICANES FORMED? • Thunderstorms • + • Ocean heat and moisture (ocean temps warmer than 26.5°C or 81°F) + High relative humidity in middle and upper troposphere + Low wind shear (change of wind speed with elevation, storms grow vertically) http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/hurr/grow/home.rxml

  8. STAGES OF DEVELOPMENT 1. TROPICAL DEPRESSION A low pressure is formed in the center of the thunderstorm group (winds 23-39mph) 2. TROPICAL STORM • Tropical depression intensifies (39-73 mph). • It is assigned a name at this time. • Strom is more circular in shape

  9. STAGES OF DEVELOPMENT 3. HURRICANE • Tropical storm becomes a hurricane when • wind speed reaches 74mph • A pronounced rotation develops around the central core

  10. INTENSITY OF HURRICANES Intensity is estimated based on: central pressure, wind speed http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/hurr/hurtrack/index.html http://www.esrl.noaa.gov/psd/data/histdata/

  11. HOW IS THE RELATIONSHIP WITH EL NIÑO? More tropical storms and hurricanes in Eastern Pacific Decrease in Atlantic, Gulf of Mexico and Caribbean sea http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/hurr/home.rxml

  12. LAST TROPICAL CYCLONES 2010 http://www.ncdc.noaa.gov/sotc/?report=hazards&year=2010&month=6&submitted=Get+Report http://www.nhc.noaa.gov/index.shtml Tropical Cyclone Phet (Arabian Sea, May 31 – June 6) • Second strongest storm developed in the Arabian Sea (Category 4) • The storm weakened and first landfall over coastal Oman (Category 2) • Flooding and landslides • ~ 300 mm of rainfall over some areas

  13. 300 mm

  14. Hurricane Alex (Atlantic, June 2010)

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