Heat and Energy Transport
in the Atmosphere
RECAP: Energy, Temperature and Heat
• Energy
•
•
1 2
E K  mv
2
♦ Kinetic
E p  mgH
♦ Potential, e.g. gravitational
Temperature scales
♦ Absolute temperature: K
♦ Fahrenheit scale: F
♦ Celsius scale: C
♦ Freezing point: 273K<->0C<->32F
♦ Boiling point: 373K<->100C<->212F
Heat capacity and specific heat capacity
♦ Large heat capacity: the object requires more energy/heat
(and it takes longer) to warm up to a certain degree.
♦ Alternatively: given the same amount of heat, the object
with the largest heat capacity warms up to the lowest T
♦ C(water) > C(soil) > C(air)
Heat Capacity
• Heat
capacity: the amount of heat energy that is required to
change the temperature of a body by 1 K.
♦ Heat capacity= Heat energy/Temperature change
Q
C
T
•
>
>
♦ It depends on the material and on the mass of the body
Specific heat capacity: the amount of energy that is required to
change the temperature of 1 gram of substance by 1 degree C.
Q
C
m T
=
♦ It does not depend on the mass of the body.
♦ It depends only on the material of the body.
>
Table 2-1, p. 30
Thermal inertia
• Bodies
with a large heat
capacity cool and/or heat up
very slowly.
♦ Analogy with a heavy body
(a big truck)
♦ Water has a high heat
capacity (large thermal
inertia) 1cal/gram/degree
♦ Regions near large bodies
of water (rivers, lakes,
oceans) do not experience
sharp temperature changes.
Their climate is mild.
♦ Air and land have smaller
specific heats than water.
Figure 3.23
Phase Changes
Phase transitions
(1 gram of water)
Sensible heat
600 cal
100C
Temperature C
Latent heat
100 cal
80 cal
0C
ICE
melting
water
HEAT IN
boiling
vapor
Latent heat
• Latent
heat: the heat required to
change a substance from one state
to another (phase change)
♦ Evaporation/Melting (cools the
environment)
♦ Condensation/Freezing (heats
the environment)
The importance
of latent heat
Heat: Q
• from one object to another.
Heat is energy in the process of being transferred
•
•
The amount of heat is equal to the change of energy
that results from the process of energy transfer.
Processes of heat transfer:
♦ Conduction;
♦ Convection;
♦ Radiation.
Heat Conduction
• Description:
•
•
•
•
♦ Transfer of kinetic energy from
one molecule to another
♦ Objects are in physical contact
Necessary conditions:
♦ Heat is conducted whenever
there is a T difference.
♦ The energy flow is from the body
of higher T towards the body with lower T
Conducting materials:
♦ Good conductors: metals
♦ Insulators (poor conductors): water, air, wood.
Conduction is NOT an efficient way to transport energy in the
atmosphere.
The heat transport through conduction near the ground is relevant
only for a thin layer a few cm thick.
Table 2-2, p. 33
Convection
• Description:
♦ Transfer of heat by mass movements of a fluid.
• Rising air cools and sinking air warms!!!
• Convection
is a very efficient way to transport energy in
fluids (gas, liquid).
• Advection: the horizontal movement of a parcel of fluid.
Development of a thermal
Fig. 2-6, p. 34
• Description:
♦ Energy carried by
electromagnetic
waves.
♦ They are NOT
mechanical waves!!!
• Characteristics:
♦ Wavelength l: the
distance between
two adjacent
peaks.
♦ Units: 1 mm
(micron)= 10-6 m
♦ May propagate
through vacuum
and “transparent”
materials.
♦ Visible: 0.4-0.7 mm
Radiation
Radiation and Temperature
• All bodies with T>0K emit radiation (electromagnetic energy).
• The
origin of the emission is the transition of the atoms
(molecules) from one energy state to another.
• The
wavelength and the amount of energy emitted by the body
depend on its temperature.
• Higher
T -> larger internal energy -> atoms vibrate faster -> the
radiation has shorter wavelength and higher energy.
The Sun’s electromagnetic spectrum
Black body radiation
Black body: it emits and absorbs at all wavelengths.
Stefan-Boltzmann Law:
Wien’s Law:
E  T
lmax
4
const.

T
Temperature and Emitted Energy
Energy
E  T 4
lmax 
const.
T
E  T 4
The Sun emits ~(6000/288)4~188,000 times more energy than the Earth!!!
•
Sun/Earth radiation
Sun
♦ T=6000 K
♦ lmax=0.5 mm
♦ Maximum in visible
•
Earth
♦ T=288 K = 15 C
♦ lmax=10 mm
♦ Maximum in IR
The Sun emits (6000/288)4~188,000 times more
energy than the Earth!!!