Solar Energy and Weather “Forecast for tonight: dark.” - George Carlin “A day without laughter is like a day without sunshine, and a day without sunshine is like, you know, night.” - Steve Martin
Heat • Thermal energy is the energy of motion of particles – such as atoms, ions, and molecules – in a substance. • Heat is defined as thermal energy transferred from one object to another. • The three mechanisms of heat transfer are conduction, convection, and radiation.
Conduction • Conduction is the mechanism of heat transfer in which highly energetic atoms or molecules collide with less energetic atoms or molecules, giving them energy. All of the atoms remain in their own place, however, only the energy transfers.
Convection • Convection is the mechanism of heat transfer in which highly energetic molecules move from one place to another.
Radiation • Radiation is the mechanism of heat transfer in which atoms or molecules emit electromagnetic waves. These waves carry the energy through space and deposit it only when they interact with some form of matter.
Solar Radiation • Radiant energy takes the form of electromagnetic waves. The electromagnetic waves that carry radiant energy from the sun to the earth fall mostly within a very narrow range of wavelengths.
Radiant Energy Reaching Earth • Because space contains very little matter, the solar energy that arrives at Earth’s outer atmosphere is essentially unchanged from when it left the sun. • The amount of radiant energy that hits one square meter of earth’s outer atmosphere every second is called the solar constant and its value is: 1367 J/m2s
Direction of Sun’s Rays • Since the amount of energy differs depending on the direction of incoming rays, the solar constant is defined for the situation in which the Sun’s rays arrive perpendicular to the surface of the earth.
The Energy Budget Diagram • Two different reactions occur when solar energy penetrates the earth’s atmosphere. • Some of the energy is reflected back into space unchanged and the rest is absorbed, either by the atmosphere or Earth’s surface.
Emission of Light • Earth, the Moon, and other planets do not emit visible light like the Sun and other stars do. You see the Moon in the night sky because of the Sun’s light being reflected off of it.
Emission of Light • Although the Moon and other planets do not emit visible light, it doesn’t mean that they do not emit electromagnetic radiation. • Objects cooler than 727oC emit radiation with wavelengths longer than that of visible light. • Earth’s radiation is in the Infrared Range of the spectrum.
Earth’s Constant Temperature • Earth maintains an energy balance and temperature by radiating as much energy out into space as it absorbs from the Sun. • The energy transformations that occur between the time solar radiation is absorbed and the time it is re-emitted as infrared radiation are the transformations that drive weather systems.
What is the only way for energy to travel from the Sun to Earth? Explain why. • Answer: • The only way for energy to travel from the Sun to Earth is by radiation. Convection and conduction require atoms, but there is nearly a complete vacuum between the Earth and the Sun.
Name the categories of electromagnetic waves that make up radiant enrgy from the Sun. • Answer: • Radiant energy from the Sun is concentrated in the infrared, visible, and ultraviolet parts of the spectrum.
Define the term “solar constant”. • Answer: • The solar constant is the amount of radiant energy from the Sun that hits one square metre of Earth’s atmosphere per second, with the square metre held perpendicular to the direction of the Sun’s rays (that is, so that an object held on that square metre would not cast a shadow).
How does Earth maintain it’s relatively constant temperature? • Answer: • Earth maintains a temperature balance by absorbing 70 percent of the sunlight falling on the hemisphere facing the Sun. It reflects 30 percent of the light and emits infrared (heat) radiation from its entire surface at all times. The atmosphere traps some of this heat and slows the cooling so that the night and daytime temperatures are fairly constant to within about 10 percent.