Weather and Climate UnitInvestigative Science

*Energy Transfer in the Atmosphere

*Thermal Energy

*All materials are made of particles (atoms and molecules), which are constantly moving in random directions. *Particles moving randomly have kinetic energy. *The total energy of the particles in an object due to their

kinetic energy is called thermal energy.

*Heat

*Heat is the transfer of thermal energy from a region of higher temperature to a region of lower temperature. *In the atmosphere, thermal energy can be transferred by radiation, conduction, and convection.

*Radiation

*Radiation is the transfer of thermal energy by electromagnetic waves. *Thermal energy is transferred from the Sun to Earth by

radiation.*The solar energy that reaches Earth is absorbed and

reflected by Earth’s atmosphere and Earth’s surface.

*Electromagnetic Spectrum

*Reflection and Absorption

*Most of the solar energy that reaches Earth is in the form of visible light waves and infrared waves. *Almost all of the visible light waves pass through the

atmosphere and strike Earth’s surface. Many of these waves are absorbed by Earth’s surface, although some are reflected back to space. *Radiation is either absorbed or reflected. However, an

object can emit energy, which means it gives off energy—but it will be

a different wavelength than it received initially.

*Rate of Absorption

*The rate of absorption for any particular area on Earth depends on the physical characteristics of the area. *Different areas absorb energy and heat up at different

rates.*Water heats and cools much slower than land does. *Darker objects absorb energy faster than light-colored

objects.

*Conduction

*Conduction is the transfer of thermal energy between objects when their atoms or molecules collide. *Conduction occurs more easily in solids and liquids

(where particles are close together) than in gases (particles are far apart).

*Conduction in Earth’s Atmosphere

*In the atmosphere, conduction occurs between Earth’s surface and the lowest part of the atmosphere.

*Convection

*Convection is the transfer of thermal energy by the movement of heated liquids or gases from one place to another. *As water or gases heat up, they expand and become less

dense. *Because it is less dense, it moves upward. *As it rises, it transfers thermal energy to the cooler gas or

liquid around it, and it cools. Then, it sinks and is re-heated.

*Convection currents

*Parcels of air near Earth’s surface are heated, become less dense than the surrounding air, and rise. *As the warm air rises, it cools and its density increases.*When it cools enough, it sinks. As it sinks, it warms again. *These movements of air are called convection currents. *This is the main mechanism of energy transfer in the

atmosphere.