Chapter 3 cont. (Heat & Temperatures)

Heat & Temperature Basics

• temperature: the energy of molecular movement• heat: a measure of the amount of energy in a

substance, often measured in calories• specific heat: the amount of heat required

(calories) to change the temperature of 1 gram of a substance by 1 degree Cwater: 1soil: ~0.2gold: .03

Which of the above will warm most w/ a given amount of energy input?

Phase Change Heat Transfer

• It takes ~585 calories to evaporate 1 gram of water (latent heat of evaporation)*

• When 1 gram of water vapor condenses to liquid form, the same 585 calories are released into the air (latent heat of condensation)

• Thus, water evaporated in tropical and subtropical oceans and carried to the middle and upper latitudes, will release large amounts of heat upon condensation. This latent heat transfer moderates temperatures in both extra-tropical and tropical regions.

• Thus, it takes 585 calories to evaporate water, but just ~100 calories to heat up water from 0° C to 100° C.

*at 20° C

Heat transfer review

• conduction: heat is transferred by molecular contact. Most important in solids.

• convection: transfer of heat by the circulation or movement of a heated liquid or gas

• radiation: energy emitted by an object or substance that travels through air or space

Principal Global Temperature Geography Controls  1. Latitude: affects insolation received & is most

significant control (Chapter 3)2. Altitude: higher elevation: ↓ annual average3. Winds and Ocean Currents (see slide “Major Ocean

Currents”)4. Continentality: places in large continents tend to have

larger annual temperature differences (see slide “Global Temp Ranges”)

5. Local effects: surface albedo, aspect6. Cloud Cover 

Effects of Latitude

Figure 3.17

Altitude

Figure 3.18

Major Ocean Currents

Figure 4.21

Land–Water Heating DifferencesLand–Water Heating Differences  • Evaporation utilizes a great deal of insolation & is most

significant in Tropics (cools the tropics)• Transparency of water allows insolation to penetrate to

depths ~ 200 feet, thus heating is not constricted to surface as much as it is on land

• The specific heat of water is very large, meaning that for a given amount of solar radiation absorbed, it warms up less than land.

• Vertical and horizontal mixing of water redistributes the heat.

• Ocean currents transport heat, and warm sea surfaces cause overlying air to be warmed

• Summary: marine environments are moderate in temperature relative to areas dominated by land.

Land–Water Heating Differences  

Figure 3.20

The GulfStream

Figure 3.21

Marine and Continental Climates

Figure 3.23

Marine and Continental Climates

Figure 3.25

January Temperatures

Figure 3.24

July Temperatures

Figure 3.26

Continentality: Global Temperature Ranges(calculated from monthly mean temps., degrees C)

Figure 3.28

The Urban Environment

Figure 3.29

Urban Heat Island

Figure 3.30

Air Temperature and the Human Body

• Wind chill– Correlates cold and wind speed

• Heat index– Correlates heat and humidity, shows the

influence of humidity on rates of evaporation