Chapter 4
Heat, Temperature, and
Driving Question
• What is the consequence of heat transfer in
the Earth-Atmosphere System?
Temperature Versus Heat
• Kinetic Energy – energy within a body that is a
result of motion
• Heat – the total energy (kinetic and potential) of
atoms or molecules composing a substance
• Temperature – a measure of the average kinetic
energy of the individual atoms or molecules
composing a system
– Temperature is NOT a type of energy, but a number
used to measure kinetic energy
Temperature Scales
• Absolute Zero – temperature in which an
objects emits no radiation
– -273.15 oC
– -459.67 oF
• Some atomic level activity still occurs
Temperature Scales
• F
= 9/5
• C = 5/9 ( F - 32 )
• K = 5/9 ( F + 459.67)
• K = C + 273.15
Heat Units
• Calorie (cal) – amount of heat needed to raise
the temperature of 1 gram of water by 1 Celsius
– This calorie has nothing to do with food calories
• British Thermal Unit (Btu) – amount of heat
needed to raise the temperature of 1 pound of
water by 1 Fahrenheit degree
• Joule (J) – most common form of measuring
• 1 cal = 4.1868J
• 1 Btu = 252cal = 1055J
Measuring Air Temperature
• Thermometer – device used to measure
variations in temperature
• Liquid in Glass
– Invented in 1593 by Galileo
– Filled with mercury (freezes at –38oF) or alcohol
(freezes at -179oF)
• Bimetallic
– Two metals bonded together (brass and iron) that bend
when heated or cooled
– Rigged to a pen and drum that records continuous
temperature - thermograph
Measuring Air Temperature
• Electrical Conductor – variations in electrical
resistance calibrated in terms of temperature
– Used in radiosondes
– Replacing liquid in glass thermometers in NWS
• Cricket chirps: temperature must be above 54oF
– # of chirps in 8 seconds + 4 = oC
• Methods for accurate measurements
– Ventilation
– Shielded from precipitation, direct sunlight, night sky
– Located away from obstacles such as trees, buildings
Heat Transfer
• Temperature Gradient – a change in
temperature with distance
• Second Law of Thermodynamics (Entropy) –
all systems tend towards disorder trying to
eliminate gradients
– Heat flows from higher temperature to lower
temperature to erase the gradient
– Larger the gradient the faster the rate of change
• Types – Conduction, Convection, Radiation
• Form of energy and energy transfer
• Can travel through a vacuum
• Principal means of EA system gaining heat from
the sun and heat escaping to space
• Radiational Heating – absorption > emission
• Radiational Cooling – absorption < emission
• Radiational Equilibrium - absorption =
• In equilibrium temperature is constant, though
different parts may be different temperatures
• Convection – transport of heat within a
fluid due to the motions of the fluid itself
– Only occurs in liquids and gases
• In the atmosphere, it is caused by
differences in air density
– Cold dry air sinks because it is more dense
– Warm moist air rises
• This air expands, cools, and sinks again
• Conduction – transfer of
kinetic energy (heat)
through collisions of
• Heat Conductivity – ratio
of the rate of heat transport
to a temperature gradient
– Solids are best conductors,
gases are worst
– Poor conductors are good
insulators (still air)
Thermal Response
• Specific Heat – the amount of heat needed to
raise 1 gram of a substance 1 degree Celsius (a
• Q = mc(ΔT)
Q: change in heat (calories, Joules)
m: mass of object (grams)
c: specific heat capacity (calories/gram oC)
ΔT: change in temperature (oC)
• A higher value of “c” indicates a greater ability to
store heat and resist temperature change
• Thermal Inertia – resistance to temperature
Thermal Response
• Because water
retains heat better
than land, areas
near the coast
have less
throughout the
Global Radiation Balance
Heat Imbalance (Surface v. Atmosphere)
• Earth’s surface undergoes net radiational
• Earth’s atmosphere undergoes net
radiational cooling
• In response to this unbalance heat is
transferred to the atmosphere from the
Sensible Heating
• Transport of heat from one place to another
by way of conduction, convection, or both
• Examples
– Warm winds blowing over snow covered
– Warm winds blowing over relatively cool
ocean surface
Latent Heat
• Latent Heat – the heat that is involved in
the phase changes of water
– Example: cloud formation
• Latent Heat of Melting (s  l)
– 80 cal/g added
• Latent Heat of Fusion (freezing: l  s)
– 80 cal/g released
Latent Heat
• Latent Heat of Vaporization (evaporation: l  g)
– 540 cal/g at 100oC added
– 600 cal/g at 0oC added
– 680 cal/g at 0oC added (sublimation: s  g)
• Latent Heat of Fusion
– Same numbers – except heat is released
– condensation: g  l
– deposition: g  s
680 cal/g
80 cal/g
Cooling of Earth’s Surface
Bowen Ratio
• BR = sensible
• For the earth
BR = 7/23 =
Heat Imbalance (Tropics v. Poles)
Heat Imbalance (Tropics v. Poles)
• Tropical Areas: incoming solar radiation is
greater than outgoing IR radiation
• Polar Areas: incoming solar radiation is
less than outgoing IR radiation
• Global Radiative Equilibrium: surplus of
solar radiation = deficit of IR radiation
• Excess heat in tropics is transported to
higher latitudes by air masses
Response to Heat Imbalance:
• Heat imbalances create temperature gradients
– Between surface and troposphere
– Between tropics and polar latitudes
• Heat is transported by conduction, convection,
clouds, air masses, storms
– Circulation of the atmosphere
• Circulation brings about changes in the state of
the atmosphere
Temperature Variations
Time and Day of year: solar intensity, angle
Cloud Cover
Surface Characteristics (albedo)
Temperature is warmer when
It is daylight
Under clear skies during the day
Under cloudy skies during the night
When the ground is not snow covered
When the ground is dry
Air Mass Advection
• Movement of an air mass from one place to
• Warm Air Advection (WAA)
– Movement of warm air
• Cold Air Advection (CAA)
– Movement of cold air
• Advection occurs when isobars and
isotherms are NOT parallel
Degree Days
• Based on 65oF
• Approximations of residential fuel
demands for heating and cooling
• Heating Degree Day
– HDD = 65oF – Average Daily Temperature
• Cooling Degree Day
– CDD = Average Daily Temperature - 65oF
Wind 0.16
• WC = 35.74 + 0.6215T – 35.75(V
– T = Temperature in Fahrenheit
– V = wind velocity in miles per hour
) + 0.4275T(V0.16)
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