(theta) dependence of intensity theta A’A >

Energy per square meter decreases at lower sun angles and shorter daylight periods.

Q0 Which curve correctly describes the solar panel output power during a day?

Goal: why the earth temperature is around 300C? --- a simple energy balance model

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 P in = (1-A) S π R Earth 2 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.

Radiation of the Earth P out = σS urface T Earth 4 S urface = 4 π R Earth 2

Earth Energy Balance Equation A Simple model: P in = P out P in = (1-A) S π R Earth 2 P out = 4 π R Earth 2 σ T Earth 4

Q1 T 4 Earth = (1-A) S /4 σ = (1- 0.3) 1367 W/m 2 /(4∙ 5.67∙10 -8 W/m 2 K 4 ) The earth temperature according to this model is 1)-100 C; 2)-18 C; 3) 30 C; 4)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: radiation/absorption.shtml 1010

Earth Energy Budget Sheet