Temperature

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Temperature

• Temperatureaverage 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 zerotemperature
  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 30close nuff most of
  the time

oC1.8 32oF
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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
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Latitude Land/water distribution Ocean
currents Elevation
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Daily temperatures

• When solar energy in gt longwave energy
  outtemperature 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 warmingbegins as conduction in layer
  nearest warm ground
• On a calm day, convection cant influence the
  lowest portion of the aircan get temperature
  profile like this

8
Effects of winds on lower atmospheric temperatures

• Wind causes forced convectionmuch more
  efficient vertical transfer of heat

9
Day Night Radiation Differences

• During day, the absorption gain from the suns
  short wave radiation is greater than the earths
  long wave radiation loss, so temperature rises.
• During night, the earths 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 aboveradiation
  inversion forms
• Temperature increases with heightusually 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

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Formation of Radiation Inversion
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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

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Atmospheric Influences on Insolation

• Absorption
• Reflection Scattering
• Transmission

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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

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Scattering
Disperse radiation in different directions
3 TYPES

• Rayleigh
• Mie
• Nonselective

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Rayleigh Scattering
Disperse radiation both forward and backward

• Leads to blue skies on a clear day
• The redness of sunsets and sunrises

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Mie Scattering
Disperse radiation predominately forward

• Effectively scatters all wavelengths therefore
  sky looks gray
• Causes sunrises to be redder

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Nonselective Scattering
Each wavelength is being refracted a different
amount
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Transmission
When solar radiation enters the atmosphere only a
fraction Makes it to the surface
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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
Earths Energy Balance
Outgoing radiation Incoming radiation