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

6000 o C 15 o C -270 o C EQUILBRIUM What is the incoming and outgoing radiation?

 -rays X-raysUVInfraredMicrowaveRadio Visible spectrum Peak energy output of sun Peak energy output at ~20 o C 10  m infrared Wavelength in micro-metres (microns or  m)

10,000 times more energy than we use 31% reflected 24% absorbed in atmosphere 45% absorbed at surface

Incoming Solar Radiation Top of atmosphere, solar constant 1.37kW/m 2 –5.5x10 24 J/year (humans use ~4x10 20 J/year) Full sun at surface, facing sun, ~1kW/m 2 But due to clouds, absorption, scattering only about 25% of sunlight, on average, reaches surface At one location only daylight ½ the time

Hobart ~135W/m 2 From Christopherson p89 Some trivia: Australians each use about 250GJ fossil fuel per year, = about 6m 2 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 CO 2 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

23.5 o 43 o S 71 o Hobart 21 Dec. Day 15 h long Above Arctic Circle – no sun South Pole – no night

23.5 o 43 o S 24 o Hobart 21 June Day 9 h long

N EW 71 o 24 o 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