Chapter 2 Solar Radiation and the Seasons

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Chapter 2 Solar Radiation and the Seasons Powered By Docstoc
					Surface Energy Balance (1)
               Review of last lecture
•   The mission of meteorology is to understand and predict weather-
    and climate-related disasters (e.g. tornados, hurricanes, El Nino and
    global warming).
•   The modern climatology (meteorology) was born in the 1940s (a very
    young science!), but has been growing very fast! Now we have a global
    observational network with many satellites, ships, radars and surface
    stations, as well as very comprehensive prediction models running on
    the world’s largest computers.
•   The current status of weather and climate predictions: (1) weather
    prediction good to 10 days, (2) tropical cyclone prediction good in
    track but not in intensity, (3) climate prediction good to two seasons,
    (4) climate change projections have a 3-fold difference in magnitude.
•   The main reasons of the difficulties: (1) Teleconnection problem, (2)
    Feedback problem, and (3) Subgrid-scale problem.
•   Importance of the ABL: (1) interface between atmosphere and
    ocean/land/ice - flux transfer and feedback, (2) the human beings are
    living in the ABL and change the environment, (3) a basic subgrid-
    scale process
             Energy basics
• Energy: the ability to do work

• Many forms: electrical, mechanical, thermal,
  chemical, nuclear, …

• Joule (J): standard unit of energy (1 J=
  0.239 calories)

• Watt (W): rate of energy flow (W = 1 J/s)
    Methods of
  Energy Transfer
• Conduction
   – Molecule to molecule transfer
   – Heat flow: warm to cold
   – e.g. leather seats in a car

• Convection
   – transferred by vertical movement
   – physical mixing
   – e.g. boiling water

• Radiation
   – propagated without medium (i.e. vacuum)
   – solar radiation provides nearly all energy
   – The rest of this chapter deals with radiation
                 Radiation
• Everything
  continually emits
  radiation

• Transfers energy in
  waves

• Waves are both
  electrical and
  magnetic, hence
  electromagnetic
  radiation
 Radiation Quantity and Quality

•Quantity: how much?  wave height
 (amplitude). Hotter bodies emit more
energy than colder bodies

• Quality: what kind?  wavelength:
distance
  btw. crest and crest (or trough and trough).
generally reported in μm (microns)- one
millionth of a meter. Hotter objects radiate at
shorter wavelengths

• Travels at the speed of light (300,000
km/s). It takes 8 minutes for light from the
Sun to reach Earth, and 4.3 years for light
from the next nearest star, Proxima Centauri
to reach us.
The Electromagnetic Spectrum
          The limitations of the
          human eye!
A man detected by different
      instruments




 Infred   Bare   X-ray   Microscope
 device   eyes
Wavelength of Sun and Earth Radiation
  Sun =
  “shortwave”
  (0.4-0.7 μm)
        Sun
  Peak 0.5 μm
  (green)



  Earth =
  “longwave”
  (4-100 μm)
  Peak 10 μm
  (infrared)
      Satellite Measurements of the
        Earth’s Radiation Budget




NASA’s Earth Radiation
Budget Satellite (ERBS)
1985-1989
           Earth’s energy budget (averaged over the
              whole globe and over a long time)

    Yellow:                                                                   Red:
    shortwave                                                                 longwave




                                        Sensible
                                        heat 7%            Net Longwave 21%
                                                           Latent heat
                                                           23%



•    At the top of the atmosphere:
     Incoming shortwave = Reflected Shortwave + Emitted longwave
•    At the surface:
     Incoming shortwave + Incoming longwave = Reflected shortwave + Emitted longwave
                         + Latent heat flux + Sensible heat flux + Subsurface Diffusion
               Net Radiation

• At the top of the atmosphere, radiation is
  balanced, i.e. (SW + LW = Net = 0)


• At the surface, on the contrary, radiation is not
  balanced, i.e., (SW + LW = Net Radiation).
 Latitudinal Variations
   in Net Radiation

• tropic-to-tropic – energy surplus
• poles – energy deficits
• ~ 38o N/S – balance

• imbalance of net radiation at surface 
  Equator/Tropics vs. high latitudes
     • drives global circulation
           • agents: wind, ocean currents,
             weather systems
Seasonal and diurnal variations
       in net radiation

• Seasonal variation
   • Summer: energy surplus
   • Winter: energy deficits

• Diurnal variation
   • Day: energy surplus
   • Night: energy deficits
Seasonal variation of surface
         radiation
           Earth’s energy budget (averaged over the
              whole globe and over a long time)

    Yellow:                                                                     Red:
    shortwave                                                                   longwave




                                        Sensible
                                        heat 7%              Net Longwave 21%
                                                             Latent heat
                                                             23%



•    At the top of the atmosphere:
     Incoming shortwave = Reflected Shortwave + Emitted longwave
•    At the surface:
     Incoming shortwave + Incoming longwave = Reflected shortwave + Emitted longwave
                                               + Latent heat flux + Sensible heat flux
                        Summary
–   What is energy? 3 methods of energy transfer

–   The names of the 6 wavelength categories in the
    electromagnetic radiation spectrum. The wavelength range
    of Sun (shortwave) and Earth (longwave) radition

–   Earth’s energy balance at the top of the atmosphere.
    Incoming shortwave = Reflected Shortwave + Emitted longwave


–   Earth’s energy balance at the surface.
    Incoming shortwave + Incoming longwave = Reflected shortwave
     + Emitted longwave + Latent heat flux + Sensible heat flux
     + Subsurface conduction

				
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