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Weather

Weather. Thunderstorms Snow / Rain storms Mid-latitude cyclones Tropical cyclones. Types of Severe Weather. Thunderstorms Snow / Rain storms Mid-latitude cyclones Blizzards Tornadoes Tropical cyclones Typhoons in the western Pacific Cyclones in the Indian Ocean

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Weather

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  1. Weather Thunderstorms Snow / Rain storms Mid-latitude cyclones Tropical cyclones

  2. Types of Severe Weather • Thunderstorms • Snow / Rain storms • Mid-latitude cyclones • Blizzards • Tornadoes • Tropical cyclones • Typhoons in the western Pacific • Cyclones in the Indian Ocean • Hurricanes in the U.S.

  3. Stages in the development of a thunderstorm

  4. Thunderstorms • How Lightning Works

  5. Thunderstorms

  6. Lightning Varieties cloud-to-ground Cloud discharge Ball lightning Blue jets Red sprites Elves (NOVA: Science Now – Lightning http://www.pbs.org/wgbh/nova/sciencenow/3214/02.html)

  7. Lightning Varieties Volcanic Lightning Nuclear Lightning Triggered Lightning (NOVA: Science Now – Lightning http://www.pbs.org/wgbh/nova/sciencenow/3214/02.html)

  8. Severe weather types • Tornadoes • How a Tornado Forms • Moist air from Gulf of Mexico • Fast moving cold, dry air mass from Canada • Jet stream moving east at 150 mph • Sets up shearing conditions

  9. Severe weather types • Tornadoes • How a Tornado Forms • Warm moist Gulf air releases latent heat, creates strong updraft • Updraft sheared by polar air, then twisted in a different direction by jet stream

  10. Tornado Wind Patterns

  11. Severe weather types • Tornadoes • Why do some thunderstorms spawn tornadoes while others do not? • Super Cell Thunderstorms

  12. Severe weather types • Tornadoes • The Fujita-Pearson Scale • The size of a tornado is not necessarily an indication of its intensity!

  13. Tornadoes • “Tornado Capitol of the World” • CNN’s “10 deadliest U.S. tornadoes” Source: cnn.com

  14. Tornadoes • Why don’t tornadoes strike large cities? • Occur over large regions • Cities are relatively small targets • Oklahoma City Tornado (1999)

  15. Mid-latitude Cyclones • Idealized weather • Middle-latitude cyclones move eastward across the United States • First signs of their approach are in the western sky • Require two to four days to pass over a region • Largest weather contrasts occur in the spring

  16. Mid-latitude Cyclones

  17. Mid-latitude Cyclones • Blizzards • Form when a long cyclone brings • Cold 60 km/hr winds • Freezing temperatures • Lots of snow • Can travel very slowly • Storm itself usually doesn’t kill • Shoveling snow, auto accidents, etc.

  18. Mid-latitude Cyclones • Ice Storms • Formation: • Falling snow and ice melt, change to rain, then freeze again as they reach the ground • Sleet • Freezing rain

  19. Hurricanes • Only natural disaster that is given a human name • Actually large tropical cyclones • Convert heat in the ocean into winds • Exports excess heat from the tropics to the midlatitudes

  20. Hurricanes • How a Hurricane Works • Tropical disturbance • Low pressure zone develops and draws in clusters of thunderstorms and winds

  21. Hurricanes • How a Hurricane Works • Tropical disturbance • Tropical depression • Surface winds strengthen, move about the center of the storm • Central core funnels warm moist air up towards stratosphere • Air cools, vapor condenses, latent heat released • Fuels more updrafts, cycle repeats, storm grows

  22. Hurricanes • How a Hurricane Works • Tropical disturbance • Tropical depression • Tropical Storm • Storm has sustained surface wind speeds of +39 mph

  23. Hurricanes • How a Hurricane Works • Tropical disturbance • Tropical depression • Tropical Storm • Hurricane • Surface winds consistently over 74 mph

  24. Hurricanes • How a Hurricane Works • Tropical disturbance • Tropical depression • Tropical Storm • Hurricane • The Eye • As wind speed increases, winds are spiraled upwards prior to reaching the center • A distinctive clear “eye” is formed • Strongest winds are located on the walls of the eye

  25. Hurricane Wind Patterns

  26. Hurricane Origins • Form in the tropics ~ 5° and 20 ° latitude • Cannot form at the equator (Coriolis effect = 0)

  27. Hurricanes • Hurricane Damages • Storm Surges • Large mound of water builds up beneath the eye • Reaches land as a surge of water

  28. Hurricanes • Hurricane Damages • Storm Surges • Wind speed varies depending upon which side of the hurricane you’re on • Amount of damage on the coastline will vary accordingly

  29. Hurricanes • Hurricane Damages • Heavy Rains • Mudflows and Debris Avalanches • Flooding

  30. Hurricanes • Hurricane paths • Curves due to Coriolis affect • Storms must go around high • Strong and large – storms to Atlantic seaboard • Small and to the north – storms may miss the U.S.

  31. Hurricane Paths

  32. Forecasting the Hurricane Season • Frequency of hurricanes in the North Atlantic is affected by climate • Wet Sahel region in Africa = more thunderstorms • Warm SST = more energy for tropical depressions • Low atmospheric pressure in Caribbean = more cyclones

  33. Forecasting the Hurricane Season • The La Nina / El Nino Connection • La Nina present in Pacific = more winds to move storms • El Nino present in the Pacific = less winds, disrupts storms

  34. El Niño

  35. Normal conditions in the tropical Pacific Ocean • Surface winds move from east to west • From high pressure in S. America to low pressure in Australia • Drags water westward • Warm water pools in the western Pacific

  36. Every 3 – 8 years, system reverses • Called the Southern Oscillation • Trade winds weaken or reverse • Warm water migrates from Australia to S. America • Arrives in time for Christmas – Corriente del Niño

  37. El Niño and La Niña

  38. What is El Niño? • Basically, it's a giant puddle (or pod) of heated water that sloshes across the Pacific Ocean • Similar to an iceberg • Bulge on the surface • Most of “pod” beneath the surface • Due to difference in density • National Geographic’s Model

  39. ENSO - El Niño-Southern Oscillation • Typically lasts 1 year • May last up to 3 • In multi-year events, first year not as affected • Affects both hemispheres

  40. Recognizing an El Niño • Sea Surface Temperatures (SST) • Normal: 6-8° C warmer in the western tropical Pacific than in the eastern tropical Pacific • Check SST to see if in “normal” range

  41. La Niña • Return to “normal” conditions from an El Niño strong • Produces: • Strong currents • Powerful upwelling • Chilly and stormy conditions along S. American coast • Eastern Pacific cools rapidly, Western Pacific warms rapidly • Renewed Trade Wind activity spreads the cooler eastern Pacific waters westward

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