Chapter 2Energy 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 ScalesTemperature 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 ScaleFahrenheit Scale

• Fahrenheit Scale (1714):

Ice melts at 320 F,

Water boils at 2120 F.

180 Degrees between melting and boiling point of pure water at sea level.

Celsius ScaleCelsius Scale

• Celsius Scale (1742):

Ice melts at 00 C

Water boils at 1000 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 ScalesTemperature Scales

Thermometers detect the Thermometers detect the movement of molecules to movement of molecules to register temperature.register temperature.

Fahrenheit and Celsius scales Fahrenheit and Celsius scales are calibrated to freezing and are calibrated to freezing and boiling water, but the Celsius boiling water, but the Celsius range is 1.8 times more range is 1.8 times more compact.compact.

Figure 2.2Figure 2.2

Temperature ScalesTemperature ScalesConversions between temperature scales can beeasily accomplished by the following three simpleequations.

C = (F - 32)59

F = C + 3295

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 TransferConduction - Heat Transfer

Figure 2.5Figure 2.5

Conduction of Conduction of heat energy heat energy occurs as occurs as warmer warmer molecules molecules transmit transmit vibration, and vibration, and hence heat, to hence heat, to adjacent adjacent cooler cooler molecules.molecules.

Warm ground Warm ground surfaces heat surfaces heat overlying air overlying air by conduction.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