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Temperature

Temperature. Temperature=average KE of molecules , or average speed of molecules:. Warm air is less dense, cool air is more dense. Temperature Scales. Kelvin scale. Based on absolute zero—temperature at which all motion stops -273 o C= -459 o F= 0 o K Centigrade (Celsius)

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Temperature

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  1. Temperature • Temperature=average KE of molecules, or average speed of molecules: Warm air is less dense, cool air is more dense

  2. Temperature Scales • Kelvin scale. Based on absolute zero—temperature at which all motion stops • -273o C= -459o F= 0o K • Centigrade (Celsius) • Water freezes at 0oC and boils at 100oC • Fahrenheit • Water freezes at 32oF and boils at 212oF…. • Converting oC to oF: Double the C temperature and then add 30…close ‘nuff most of the time oC*1.8 + 32=oF

  3. Influences on Temperature • Latitude • Altitude • Atmospheric circulation • Contrasts between land and water • Warm and cold ocean currents • Local impacts on temperature

  4. Isotherms: Lines of equal temperature

  5. Latitude Land/water distribution Ocean currents Elevation

  6. Daily temperatures • When solar energy in > longwave energy out—temperature rises • Maximum occurs in late afternoon...clouds, haze, humidity, and ground cover control timing and maximum value Radiational Cooling Solar Heating

  7. Daily Temperature Variations • Daytime warming—begins as conduction in layer nearest warm ground • On a calm day, convection can’t influence the lowest portion of the air—can get temperature profile like this:

  8. Effects of winds on lower atmospheric temperatures • Wind causes “forced convection”—much more efficient vertical transfer of heat

  9. Day – Night Radiation Differences • During day, the absorption gain from the sun’s short wave radiation is greater than the earth’s long wave radiation loss, so temperature rises. • During night, the earth’s long wave radiation loss is greater, so temperature falls.

  10. Radiation Inversion • Air temperature usually decreases with height (lapse rate) • At night, ground cools, and air near ground can become much cooler than air above—radiation inversion forms • Temperature increases with height—usually not much higher than 300 feet above the ground • Extremely stable conditions —fog often forms as air reaches Dew Point temperature • Long nights, calm winds, dry and cloud-free atmosphere are most favorable conditions for inversion formation

  11. Formation of Radiation Inversion

  12. Forecast: Cooler or Warmer?? • Daytime: Coastal city vs. Inland city? • Nighttime: Coastal city vs. Inland city? • Daytime: city with clear skies vs. city with cloudy skies • Nighttime: city with clear skies vs. city with cloudy skies • Daytime: city at 6,000ft vs. city at sea level • Nighttime: city at 300ft vs. city at sea level

  13. Atmospheric Influences on Insolation • Absorption • Reflection & Scattering • Transmission

  14. Absorption Atmospheric gases, particulates, and droplets all reduce the intensity of solar Radiation EFFECTS • The absorber gains energy and warms • The amount of energy delivered to the surface is reduced

  15. Reflection Reflection: radiation is redirected away from the surface without being absorbed Albedo: The percentage of visible light reflected • TWO TYPES: • Specular Reflection • Diffuse Reflection

  16. Scattering Disperse radiation in different directions 3 TYPES • Rayleigh • Mie • Nonselective

  17. Rayleigh Scattering Disperse radiation both forward and backward • Leads to blue skies on a clear day • The redness of sunsets and sunrises

  18. Mie Scattering Disperse radiation predominately forward • Effectively scatters all wavelengths therefore sky looks gray • Causes sunrises to be redder

  19. Nonselective Scattering Each wavelength is being refracted a different amount

  20. Transmission When solar radiation enters the atmosphere only a fraction Makes it to the surface

  21. Transmission & The Fate of Solar Radiation • 100 units available at the top of the atmosphere • Atmosphere absorbs 25 units • 7 units are UV radiation absorbed by ozone • Remainder is IR radiation absorbed by gases • Clouds reflect 19 units back to space • Gases and aerosols scatter 6 units back to space • 50 units reach the surface • 5 units scattered back to space

  22. Earth’s Energy Balance Outgoing radiation = Incoming radiation

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