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Atmospheric Hazards

Atmospheric Hazards

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Atmospheric Hazards

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  1. Atmospheric Hazards Thunderstorms, Tornadoes, High Winds, and Fog Session 7

  2. Pure Air • Invisible • Colorless • Odorless • Tasteless

  3. Atmospheric Composition • Gases • Liquid and Solid Matter

  4. Atmospheric Gases • Nitrogen 78% of volume • Oxygen 21% • Others combined approximately 1% • Includes Argon, Neon, Helium, Methane, Krypton, and Hydrogen

  5. Variable-Amount Gases • Water Vapor • Carbon dioxide • Carbon Monoxide • Ozone • Sulfur dioxide • Nitrogen dioxide

  6. Atmospheric Composition

  7. Liquid and Solid Matter • Liquid: Water • < 1% by volume • Solids: Ice Crystals • < 1% by volume • Particulate matter • < 1% by volume

  8. Particulate Matter • Tiny solids such as dust, smoke, soil, ash, salt spray, and pollutants • May be suspended in the atmosphere for long periods of time (years) • Most particulate matter close to source of origin but can travel great distances both horizontally and vertically

  9. Affects on Weather • Hygroscopic (absorb water) so water vapor condenses around particulates affecting cloud formation • Absorb or reflect insolation changing the amount of solar radiation reaching the surface

  10. Atmospheric Pressure • Atmosphere has weight, pressing downward • Molecules of air create air pressure through their motion, size, and number • Pressure exerted on all surfaces in contact with the air • Same pressure inside us pushing outward so we are not crushed

  11. More Pressure • Average force 14.7 lb/in.2 • Normal pressure 1013.2 mb (29.92”) • Density decreases with altitude • 50% of molecules are below 3.5 miles and 90% in 10 miles

  12. Thermal Layers • Troposphere • Stratosphere • Mesosphere • Thermosphere • Exosphere

  13. Layers of the Atmosphere

  14. Troposphere • Lowest region of the atmosphere • Name implies vertical mixing of air • Usually a steady decrease in temperature with an increase in altitude • 3.5° per 1000’ (6.4°/1000m) • Lapse Rate

  15. Inversions • Increase in air temperature with increase in altitude • Can trap air pollution

  16. Tropospheric Characteristics • Most moisture and heat located here • Most weather occurs • Depth an average of 11 miles from surface at equator and 5 miles at the poles • Fluctuates during seasons

  17. Stratosphere • Roughly 11 miles to 31 miles above the surface • Strong inversion exists due to absorption of uv radiation from the Sun • Contains ozone (O3) layer to absorb this radiation • Transition zone called stratopause

  18. Mesosphere • Temperature decreases with height • Due to distance from ozone layer • Approximately 31 to 50 miles above the Earth’s surface • Top of layer bounded by an isothermal layer called the Mesopause

  19. Thermosphere • Dramatic decrease in heat energy content • BUT very high temperature (2200° F) • Due to lack of mass • Approximately 50 to 300 miles above the Earth’s surface (lower in less active solar activity, 155 miles) • Isothermal layer called the Thermopause

  20. Exosphere • 300 miles out to 20,000 miles from the surface • Outer space • Atmosphere is rarefied, practically a vacuum • Few hydrogen and helium atoms weakly bound by gravity

  21. What is Weather?

  22. Weather • Short term atmospheric conditions that exist for a given time in a specific location • Can be sum of variables such as temperature, cloudiness, humidity, precipitation, wind, storms, and pressure • Temporal parameters can be moment, day, week, season, year, or decade

  23. What is Climate?

  24. Climate • Aggregate of day-to-day weather conditions over a long period of time • Includes both average characteristics along with the variations and extremes • Normally 30 years for climate studies

  25. Major Elements of Weather and Climate • Temperature • Pressure • Wind • Moisture Content

  26. Principal Climate and Weather Controls • Latitude • Land and water distribution • General circulation of the atmosphere • General circulation of the oceans • Elevation • Topographic barriers • Storms

  27. Latitude • Latitude influences temperature • Positional relationship between Earth and Sun • Varying amounts of radiant energy

  28. Land and Water Distribution • Moisture content and temperature • Continental versus maritime climates • Oceans heat and cool slower than landmasses • Source of moisture • Uneven distribution of land and water

  29. General Circulation of the Atmosphere • Semipermanent pattern of wind and pressure systems in the troposphere • Local wind to regional patterns • Winds in the tropics from east while midlatitudes from west

  30. General Circulation of the Oceans • Heat transfer with currents • Warm water poleward and cool water towards the equator • Warm currents off east coasts of continents • Cool currents off west coasts of continents

  31. Elevation • Temperature, pressure, and moisture content decrease with increase in elevation • Influence in mountainous areas

  32. Topographic Barriers • Mountains and hills have effects on climate elements • Lake effect snow • Windward and leeward side of mountains

  33. Storms • Local thunderstorm • Tornado • Hurricane • Monsoon • Blizzard • Mid Latitude Cyclone

  34. What are the Characteristics of a Thunderstorm?

  35. Thunderstorms • Heavy rain • Lightning • Flash Flooding • Hail • Wind • Tornadoes

  36. What is a Severe Thunderstorm?

  37. Severe Thunderstorms • Winds > 50 kts (58 mph) • Hail ≥ 1” • Tornado

  38. Life Cycle • Three Main Stages • Initial • Mature • Dissipation

  39. Initial Stage • Towering Cumulus Stage • Persistent updraft and rapidly growing vertical cloud • Expanding cloud diameter

  40. Mature Stage • Updraft strength reaches maximum height • Some storm tops over 25,000’-60,000’ agl • Lightning at beginning of mature stage • Rainfall begins and forces downdraft • Microbursts • Hail • Gust front • Pool of cool air at surface

  41. Dissipation Stage • Dome of cool air cuts off updraft at surface and causes storm to die out • Edge of dome is now in outflow boundary, potential for new thunderstorms to form • Possible tornado formation due to enhanced low-level horizontal shear

  42. Thunderstorm Stages

  43. Types of Thunderstorms

  44. Forms of Thunderstorms • Squall Line: organized line of individual cells (downbursts, straight-line winds) • Multicell Cluster (MCC): strong updrafts (hail, heavy precipitation); can exist for hours • Supercell: strong updrafts and vertical wind shear (potential mesocyclones and tornadoes); large hail and downbursts

  45. Supercell

  46. Thunderstorm Distribution

  47. Lightning Fatalities

  48. Thunderstorm Case Studies • Nashville, Tennessee • Ouachita National Forest, Arkansas

  49. Nashville, Tennessee • May 1-2, 2010 • 13+” rain • 29 fatalities in southern United States • http://www.srh.noaa.gov/ohx/?n=may2010epicfloodevent

  50. Ouachita National Forest • June 11, 2010 • 5+” rain • River estimated to rise 8’/hour • 20 fatalities