second region in which the temperature increases with
height, extends from the mesopause to the exosphere.
EXOSPHERE.The very outer limit of Earths
atmosphere is regarded as the exosphere. It is the zone
in which gas atoms are so widely spaced they rarely
collide with one another and have individual orbits
classification is the effect on communications and
radar. The electrical classification outlines three
zonesthe troposphere, the ozonosphere, and the
TROPOSPHERE.The troposphere is important
to electrical transmissions because of the immense
changes in the density of the atmosphere that occur in
this layer. These density changes, caused by differences
in heat and moisture, affect the electronic emissions
that travel through or in the troposphere. Electrical
waves can be bent or refracted when they pass through
these different layers and the range and area of
communications may be seriously affected.
coincident with the stratosphere. As was discussed
earlier in this section, the ozone is found in this zone.
Ozone is responsible for the increase in temperature
with height in the stratosphere.
IONOSPHERE.The ionosphere extends from
about 40 miles (200,000 ft or 64 kilometers) to an
indefinite height. Ionization of air molecules in this
zone provides conditions that are favorable for radio
propagation. This is because radio waves are sent
outward to the ionosphere and the ionized particles
reflect the radio waves back to Earth.
The atmosphere is constantly gaining and losing
heat. Wind movements are constantly transporting heat
from one part of the world to another. It is due to the
inequalities in gain and loss of heat that the air is almost
constantly in motion. Wind and weather directly
express the motions and heat transformations.
In meteorology, one is concerned with four
conduction, convection, advection, and radiation. Heat
is transferred from Earth directly the atmosphere by
conduction, and convection. Advection, a form of
convection, is used in a special manner in meteorology.
It is discussed as a separate method of heat transfer. As
radiation was discussed earlier in the unit, this section
covers conduction, convection, and advection.
CONDUCTION.Conduction is the transfer of
heat from warmer to colder matter by contact. Although
of secondary importance in heating the atmosphere, it is
a means by which air close to the surface of Earth heats
during the day and cools during the night.
CONVECTION.Convection is the method of
heat transfer in a fluid resulting in the transport and
mixing of the properties of that fluid. Visualize a pot of
boiling water. The water at the bottom of the pot is
heated by conduction. It becomes less dense and rises.
Cooler and denser water from the sides and the top of
the pot rushes in and replaces the rising water. In time,
the water is thoroughly mixed. As long as heat is
applied to the pot, the water continues to transfer heat
by convection. The transfer of heat by convection in
this case applies only to what is happening to the water
in the pot. In meteorology, the term convection is
normally applied to vertical transport.
Convection occurs regularly in the atmosphere and
is responsible for the development of air turbulence.
Cumuliform clouds showers and thunderstorms occur
when sufficient moisture is present and strong vertical
convection occurs. Vertical transfer of heat in the
atmosphere (convection) works in a similar manner.
Warmer, less dense air rises and is replaced by
descending cooler, denser air, which acquires heat.
The specific heat of a substance shows how many
calories of heat it takes to raise the temperature of 1
gram of that substance 1°C. Since it takes 1 calorie to
raise the temperature of 1 gram of water 1°C, the
specific heat of water is 1. The specific heat of a
substance plays a tremendous role in meteorology
because it is tied directly to temperature changes. For
instance, the specific heat of earth in general is 0.33.
This means it takes only 0.33 calorie to raise the
temperature of 1 gram of earth 1°C. Stated another way,
earth heats and cools three times as fast as water.
Therefore, assuming the same amount of energy
(calories) is available, water heats (and cools) at a