Solar constant

1. Solar constant The solar constant is the amount of incoming solar radiation per unit area, measured on the outer surface of Earth's atmosphere, in a plane perpendicular to the rays. • Solar constant for Earth, S = 1350 W/m2

2. Albedo Albedo is the fraction of sunlight which is reflected off a planet. When an object reflects most of the light that hits it, it looks bright and it has a high albedo.  When an object absorbs most of the light that hits it, it looks dark.   Dark objects have low albedo. .

3. Earth’s Albedo • The average albedo of the Earth is about 0.30. • That means that about a third of the solar energy that gets to Earth is reflected out to space and about two thirds is absorbed

4. One layer model Assumptions: No atmosphere

5. Energy Balance Pin = Pout Pin = (1-A) S π RE2 Pout = σ TE4 4π RE2 (1-A) S = σ TE4 4

6. Energy Balance of the One layer model Solar radiation Earth Earth’s infrared radiation to space σT4E (1-A) S 4 Tearth = 257 K = -16° C = 3.2°F

7. Calculating Surface Temperature of the Earth σ T4 = S x ( 1- A) 4 Where S - Solar constant σ – Stephan constant - 5.67 x 10-8 W/m2K4 A - Albedo