1. The Sun provides all the energy to drive Earth’s climate 2. Climate is sensitive to small changes in sunlight that occur on astronomical-to-annual timescales 3. Pollution can influence altering reflectivity of clouds, snow, and ice, which in turn trigger powerful climate feedbacks1. Sunlight, Clouds, and Climate • What is the spectral distribution of sunlight? • How does insolation vary on astronomical timescales? • How is absorbed sunlight partitioned in the climate system? • What role do clouds play? • How do particles and sunlight interact? 2. Definitions • Climate: Average patterns of temperature, rainfall, wind... – Averages taken over 1000’s of miles, many years – Climate is intrinsically noisy (butterfly effect) • Radiation: A form of energy emitted by matter – “Electromagnetic radiation ” = “Radiation ” = “Light ” = “Photons” – Photons are Light → travel at the speed of light – Photons travel like waves (with a wavelength) ∗ Shorter wavelengths (bluer) are more energetic ∗ Longer wavelengths (redder) are less energetic3. What form of Radiation is Sunlight? Sunlight: Thermal (radiation) energy emitted by the Sun • “Sunlight ” = “Solar radiation ” = “Shortwave Radiation ” = “Solar energy” • Most sunlight energy in 0.4–0.7 × 10−6 meters (microns) • Peak wavelength is green (0.5 microns) • Known as visible wavelengths: blue → re
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