Post on 18-Dec-2015
(theta) dependence of intensity
theta
A’ A>
Q1
The earth will be a warmer place if
A) it is further away from the sun;
B) the surface temperature of the sun is lower;
C) the solar constant is bigger;
D) none of above.
Q2
Solar constant (1367W/m^2) near the earth increases if
A) the earth is closer to the sun;
B) The surface temperature increases;
C) Both a) and b) are true.
D) None is true.
Q3 (survey question)
The earth surface temperature is about 15C mainly because
A) Solar constant is 1367W/m^2;
B) Green house gases;
C) Thermal heat from the core of the earth;
D) Both A) and B)
Energy Balance
Incoming solar radiation power (depends on the value of solar constant, or how far the earth is from the Sun)
=
Outgoing radiation emitted by the earth
(depends on the earth temperature)
Power of the incoming radiation
Pin = (1-A) S π REarth2
Example from Roland B. Stull, Meteorology for Scientist and Engineers
Reflection coefficients or Albedo
• Overall average reflection coefficient of an object: Albedo
• Albedo of the Earth is about A = 0.3 which means that the Earth as a whole reflects 30% of solar radiation.
Earth Energy Balance Equation
A Simple model: Pin = Pout
Pin = (1-A) S π REarth2
Pout = 4π REarth2 σ TEarth
4
Q1
T4Earth = (1-A) S /4 σ
= (1- 0.3) 1367 W/m2/(4∙ 5.67∙10-8 W/m2K4)
The earth temperature according to this model is
• -100 C;• -18 C;• 30 C;• 100C.
• So we actually obtained a temperature of the Earth as seen from far away – the temperature of the atmosphere, not the surface temperature!!
• What are the effects of atmosphere ??
Atmospheric Absorption
• From: http://www.everythingweather.com/atmospheric-radiation/absorption.shtml
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