Earth's Radiation Balance and the Seasons

Document Sample
Earth's Radiation Balance and the Seasons Powered By Docstoc
					  Earth’s Radiation Balance
       and the Seasons
          Geog 1, Week 3, March 12
  Chapters 2 and 4 of Christopherson

             Need to Know
Energy flow through the atmosphere
Energy changes with latitude and season
                               -270oC

     6000oC




                                               15oC

EQUILBRIUM

What is the incoming and outgoing radiation?
           Wavelength in micro-metres (microns or m)
10-8             0.01   0.4-0.7             103    106

  -rays    X-rays   UV           Infrared Microwave Radio




                                                   10m
                                                   infrared
                    Visible spectrum              Peak energy
                Peak energy output of sun         output at ~20oC
 10,000 times more    24% absorbed in atmosphere
 energy than we use


31% reflected
                                 45% absorbed
                                 at surface
     Incoming Solar Radiation
• Top of atmosphere, solar constant
  1.37kW/m2
  – 5.5x1024 J/year (humans use ~4x1020 J/year)
• Full sun at surface, facing sun, ~1kW/m2
• But due to clouds, absorption, scattering
  only about 25% of sunlight, on average,
  reaches surface
• At one location only daylight ½ the time
From Christopherson p89




                                                        Hobart
                                                        ~135W/m2

                          Some trivia: Australians each use about
                          250GJ fossil fuel per year, = about 6m2 in
                          Hobart
All the energy
absorbed by the
air and surface is
radiated back
out into space


                     Radiation
                     Convection
                     Evaporation/
                     Condensation
                     (latent heat)
        Outgoing Radiation
• Infrared with a peak intensity at about
  10m
• Gases such as CO2 absorb some of this
  infrared radiation, hence concern about
  global warming
• Cloudy night is warmer because
  radiation cannot ‘escape’ to space
From Christopherson p95
                  Part 2
• Having discussed radiation in and out
• Now it is important to consider the effect
  of latitude on heating of the surface
• And the fact that the tilt of the Earth’s
  axis means different latitudes will get
  more or less radiation at different times
  of the year.
             The Seasons
• Solar System
• Earth about 150,000km from sun
           Above Arctic Circle – no sun
                                   23.5o




             71o

Hobart 21 Dec.
Day 15 h long


  South Pole – no night
23.5o




        24o

              Hobart 21 June
              Day 9 h long
                   71o



                        24o

  W                 N                   E


Summer and Winter Sun Paths for Hobart

Very important for solar house design
               Summary
•   Radiation from sun
•   Radiation from Earth
•   More incoming energy near equator
•   Earth’s tilt:- seasons
             Next Week
• Global Circulation (Synoptic Winds)
• Chapter 6 of Christopherson
• Especially pages 140 to 155

				
DOCUMENT INFO
Shared By:
Categories:
Tags:
Stats:
views:17
posted:3/6/2012
language:English
pages:17