theta dependence of intensity theta A A

(theta) dependence of intensity theta A’ > A

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

Q 0 Which curve correctly describes the solar panel output power during a day?

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

Q 1 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.

Q 2 Solar constant (1367 W/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.

Q 3 (survey question) The earth surface temperature is about 15 C mainly because A) Solar constant is 1367 W/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 REarth 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 • Pout = σSurface TEarth Surface = 4 π REarth 4 2

Earth Energy Balance Equation A Simple model: Pin = Pout Pin = (1 -A) S π REarth 2 Pout = 4π REarth 2 σ TEarth 4

Q 1 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 • • -100 C; -18 C; 30 C; 100 C.

• 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 1 0 • From: http: //www. everythingweather. com/atmosphericradiation/absorption. shtml

Earth Energy Budget Sheet