Chapter 5, Heat and Temperature 5-8
Figure 5-5. Heat Transfer Examples1
5.7 Thermal Response
Whether by radiation, conduction, convection, or a combination of these, the temperature response to the
input (or output) of some specified quantity of heat varies from one substance to another. Specific heat is
defined as the measure of heat energy required to increase the temperature of a unit quantity of a substance
by a certain temperature interval. Specific heat capacity is typically expressed in uni ts of joules per gram-
kelvin (J g-1 K-1). Thus, two different substances with identical temperature measurements do not
necessarily possess the same amount of heat energy. When exposed to the same amount of heat energy, a
substance with a low specific heat warms up more than a substance with a higher specific heat . Table 5-4
lists the specific heat capacity of various substances.
1 The source of this and other material labeled COMET® is the COMET® website at https://www.meted.ucar.edu of
the University Corporation for Atmospheric Research (UCAR), sponsored in part through cooperative agreement(s)
with NOAA, U.S. DOC. ©1997-2017 University Corporation for Atmospheric Research. All Rights Reserved.
Chapter 5, Heat and Temperature 5-9
Table 5-4. Specific Heat of Various Substances
Substance Phase Specific Heat
(J g-1 K-1)
Water (steam) Gas (100 °C) 4.22
Water Liquid (25 °C) 4.18
Wood (balsa) Solid 2.90
Water (ice) Solid (0 °C) 2.05
Wood (oak) Solid 2.00
Soil (wet) Solid 1.48
Sandy clay Solid 1.38
Air (sea level, dry) Gas 1.01
Asphalt Solid 0.92
Clay Solid 0.92
Aluminum Solid 0.91
Brick (common) Solid 0.90
Concrete Solid 0.88
Glass Solid 0.84
Limestone Solid 0.84
Sand (quartz) Solid 0.83
Soil (dry) Solid 0.80
Granite Solid 0.79
Iron Solid 0.46
Copper Solid 0.39
Mercury Liquid 0.14
Lead Solid 0.13
All measurements are at 25 °C unless otherwise noted.
Note: 1 K equals -272.15 °C.
Water has the highest specific heat of any naturally occurring substance. That means it has a much higher
capacity for storing heat energy than other substances, such as soil, sand, rock, or air. Water can store large
amounts of heat energy while only experiencing a small temperature change.
Figure 5-6 compares the specific heat of water and sand. The specific heat of water is more than five times
that of quartz sand. Thus, 4.18 J of heat are required to raise the temperature of 1 gram (g) of water by 1 °C,
while only 0.83 J are required to raise the temperature of 1 g of quartz sand by 1 °C. This is one reason why
beach sand is hotter than water on a sunny, summer afternoon.
Chapter 5, Heat and Temperature 5-10
Figure 5-6. Specific Heat Capacity: Water versus Sand
The difference in the specific heat of various materials is one of the primary reasons why the temperature
of a body of water, such as a lake or the ocean, is less variable with time than the surface temperature of
land. Water heats up more slowly than land during the day and during the summer and cools down more
slowly at night and during the winter. Thus, a body of water exhibits greater resistance to temperature
change (called thermal inertia) than does a land mass.
Heat flow differences are another reason why water bodies warm up and cool down more slowly than land.
Incoming solar radiation penetrates water to significant depths but can only heat the top skin layer of soil
and rock. Also, since water is a fluid, its heat energy can be circulated through great volumes and depths
via convection. Water temperature changes occur to depths of 6 meters (m) (20 ft) or more on a daily basis,
and 200 m to 600 m (650 ft to 1950 ft) annually. The process is more problematic over land since heat must
be transferred via the slow process of conduction. Land temperature changes occur to de pths of only
10 centimeters (cm) [4 inches (in)] on a daily basis and 15 m (50 ft) or less annually.
Water is much more resistant to temperature changes than land. It warms up and cools down more slowly
than land and helps to moderate nearby air temperature. This is why islands and localities located
immediately downwind from the ocean or a large lake (ma ritime locations) exhibit smaller diurnal and
seasonal temperature variations than localities well inland (continental locations). Figure 5-7 illustrates this
effect. Although both cities are at approximately the same latitude, the temperature is far less variable in
San Francisco (maritime) than St. Louis (continental).
Chapter 5, Heat and Temperature 5-11
Figure 5-7. Variation of Mean Daily Temperatures for San Francisco (Maritime) and St. Louis (Continental)
5.8 Temperature Variations with Altitude
A lapse rate of temperature is defined as a decrease in temperature with height. In Figure 4-2, it was stated
that the temperature decreases 6.5 °C/km (3.57 °F/1,000 ft) in the standard atmosphere. But since this is an
average, the exact value seldom exists. In fact, temperature in the troposphere sometimes remains constant
or even increases with height. Caution should be taken when using the standard lapse rate to estimate the
freezing level. Quite often the boundary layer is dry adiabatic , and the estimate of freezing level could be
in error.
5.8.1 Atmospheric Sounding
An atmospheric sounding, or simply sounding, is a plot of the vertical profile of one or more atmospheric
parameters, such as temperature, dewpoint, or wind above a fixed location. Soundings are used extensively
by meteorologists to determine the state of the atmosphere.
5.8.2 Isothermal Layer
An isothermal layer is a layer within the atmosphere where the temperature remains constant with height
(see Figure 5-8).
Chapter 5, Heat and Temperature 5-12
Figure 5-8. Sounding with an Isothermal Layer
5.8.3 Temperature Inversion
A temperature inversion, or simply inversion, is a layer in which the temperature increases with altitude. If
the base of the inversion is at the surface, it is termed a surface-based inversion. If the base of the inversion
is not at the surface, it is termed an inversion aloft (see Figure 5-9).
A surface-based inversion typically develops over land on clear nights when wind is light. The ground
radiates and cools much faster than the overlying air. Air in contact with the ground becomes cool, while
the temperature a few hundred feet above changes very little. Thus, temperature increases with height.
An inversion may also occur at any altitude when conditions are favorable. For example, a current of warm
air aloft overrunning cold air near the surface produces an inversion aloft. Inversions are common in the
stratosphere.
The principal characteristic of an inversion layer is its marked stability, so that very little turbulence can
occur within it. Turbulence will be discussed at length in Chapter 19, Turbulence.
Chapter 5, Heat and Temperature 5-13
Figure 5-9. Sounding with a Temperature Inversion