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Explore the composition of the atmosphere, thermal layers, weather phenomena, and climate controls. Learn about atmospheric gases, pressure, layers, and factors influencing weather and climate. Discover the importance of elements like temperature, wind, and moisture content.
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Atmospheric Hazards Thunderstorms, Tornadoes, High Winds, and Fog Session 7
Pure Air • Invisible • Colorless • Odorless • Tasteless
Atmospheric Composition • Gases • Liquid and Solid Matter
Atmospheric Gases • Nitrogen 78% of volume • Oxygen 21% • Others combined approximately 1% • Includes Argon, Neon, Helium, Methane, Krypton, and Hydrogen
Variable-Amount Gases • Water Vapor • Carbon dioxide • Carbon Monoxide • Ozone • Sulfur dioxide • Nitrogen dioxide
Liquid and Solid Matter • Liquid: Water • < 1% by volume • Solids: Ice Crystals • < 1% by volume • Particulate matter • < 1% by volume
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
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
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
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
Thermal Layers • Troposphere • Stratosphere • Mesosphere • Thermosphere • Exosphere
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
Inversions • Increase in air temperature with increase in altitude • Can trap air pollution
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
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
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
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
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
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
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
Major Elements of Weather and Climate • Temperature • Pressure • Wind • Moisture Content
Principal Climate and Weather Controls • Latitude • Land and water distribution • General circulation of the atmosphere • General circulation of the oceans • Elevation • Topographic barriers • Storms
Latitude • Latitude influences temperature • Positional relationship between Earth and Sun • Varying amounts of radiant energy
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
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
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
Elevation • Temperature, pressure, and moisture content decrease with increase in elevation • Influence in mountainous areas
Topographic Barriers • Mountains and hills have effects on climate elements • Lake effect snow • Windward and leeward side of mountains
Storms • Local thunderstorm • Tornado • Hurricane • Monsoon • Blizzard • Mid Latitude Cyclone
Thunderstorms • Heavy rain • Lightning • Flash Flooding • Hail • Wind • Tornadoes
Severe Thunderstorms • Winds > 50 kts (58 mph) • Hail ≥ 1” • Tornado
Life Cycle • Three Main Stages • Initial • Mature • Dissipation
Initial Stage • Towering Cumulus Stage • Persistent updraft and rapidly growing vertical cloud • Expanding cloud diameter
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
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
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
Thunderstorm Case Studies • Nashville, Tennessee • Ouachita National Forest, Arkansas
Nashville, Tennessee • May 1-2, 2010 • 13+” rain • 29 fatalities in southern United States • http://www.srh.noaa.gov/ohx/?n=may2010epicfloodevent
Ouachita National Forest • June 11, 2010 • 5+” rain • River estimated to rise 8’/hour • 20 fatalities