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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 C
water: 1
soil:
~0.2
gold:
.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.
2.
3.
4.
5.
6.
Latitude: affects insolation received & is most
significant control (Chapter 3)
Altitude: higher elevation: ↓ annual average
Winds and Ocean Currents (see slide “Major Ocean
Currents”)
Continentality: places in large continents tend to have
larger annual temperature ranges (see slide “Global
Temp Ranges”)
Local effects: surface albedo, aspect
Cloud Cover
Effects of
Latitude
Figure 3.17
Altitude
Figure 3.18
Major Ocean Currents
Figure 4.21
Land–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 Gulf
Stream
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