Chapter 2 Energy in the Atmosphere

Energy It’s what makes things happen

What’s it about? Temperature, Energy and Heat TODAY: Temperature –Temperature scales

Definitions Before we start we need to get some things straight We need definitions of some basic atmospheric parameters

Content Basics –The basic properties of the air Temperature Pressure Density –We’ve already met the latter two

Temperature: The temperature of a substance is a measure of the average kinetic energy of the molecules in that substance. Thus atmospheric temperature is proportional to the speed of the air molecules. Temperature

Temperature Scales There are three (3) temperature scales you need to know about. With their units: Fahrenheit (  F) -- German Celsius (  C) -- Swedish Absolute (K) -- Scientific

Fahrenheit Scale Fahrenheit Scale (1714): Ice melts at 32 0 F, Water boils at F. 180 Degrees between melting and boiling point of pure water at sea level.

Celsius Scale Celsius Scale (1742): Ice melts at 0 0 C Water boils at C  One of several “Centigrade Scales.” 100 Degrees between melting and boiling point of pure water at sea level.

Thermodynamic (Kelvin) Scale Kelvin or Absolute Scale (1800’s): –No molecular motion at 0 K. –Uses Celsius’ degree increment Ice melts at 273 K Water boils at 373 K

Temperature Scales Thermometers detect the movement of molecules to register temperature. Fahrenheit and Celsius scales are calibrated to freezing and boiling water, but the Celsius range is 1.8 times more compact. Fahrenheit and Celsius scales are calibrated to freezing and boiling water, but the Celsius range is 1.8 times more compact. Figure 2.2

Temperature Scales Conversions between temperature scales can be easily accomplished by the following three simple equations.  C = (  F - 32) 5 9  F =  C K =  C + 273

Energy Energy - The ability to do work or exchange heat with the surroundings. Examples of types of energy –Potential Energy -- Energy of position –Kinetic Energy -- Energy of motion –Internal Energy -- Energy of motion of the molecules. –Radiant Energy -- Electromagnetic radiation.

First Law of Thermodynamics In a system with constant mass, energy can be neither created or destroyed. Energy is conserved. Energy may be changed to a different form. Example: The change in kinetic energy may go to a change in potential or internal energy.

Second Law of Thermodynamics It is impossible to construct a device to transfer heat from a colder system to a warmer system without the occurrence of other simultaneous changes in the two systems or the environment. Heat transfer is one way: Hot to cold.

Heat Energy in the process of being transferred from one object to another (due to temperature differences)

Heat Transfer How is heat transferred? –Latent Heat –Conduction –Convection –Radiation

Temperature Gradient A gradient is the change in something over a given distance. A temperature gradient is the change in temperature over a given distance. A gradient has both magnitude and direction. The gradient points in the direction of maximum (temperature) change toward higher values. Consider an example………...

Conduction - Heat Transfer Figure 2.5 Conduction of heat energy occurs as warmer molecules transmit vibration, and hence heat, to adjacent cooler molecules. Warm ground surfaces heat overlying air by conduction. Warm ground surfaces heat overlying air by conduction.

Temperature Gradient Heat transfer occurs in the direction of hotter regions to colder regions. If there is a temperature gradient, the heat transfer will act to destroy the gradient.

Summary We now know what the following are: –Temperature –Energy –Heat