lightning first occurs between the upper positive charge
area and the negative charge area immediately below it.
Lightning discharges are considered to occur most
frequently in the area bracketed roughly by the 32°F
and the 15°F temperature levels. However, this does not
mean that all discharges are confined to this region; as
the thunderstorm develops, lightning discharges may
occur in other areas and from cloud to cloud, as well as
from cloud to ground.
There are four main types of lightning. All can do
considerable damage to aircraft, especially to radio
equipment.
1.
Cloud To Ground Lightning (CG). Lightning
occurring between cloud and ground.
2.
Cloud Discharges (IC). Lightning taking place
within the cloud.
3.
Cloud To Cloud Discharges (CC). Streaks of
lightning reaching from one cloud to another.
4.
Air Discharges (CA). Streaks of lightning
passing from a cloud to the air that do not strike the
ground.
AURORAS
Auroras are luminous phenomena, which appear in
the high atmosphere in the form of arcs, bands,
draperies, or curtains. These phenomena are usually
white but may have other colors. The lower edges of the
arcs or curtains are usually well defined while the upper
edges are not. Polar auroras are caused by electrically
charged particles, ejected from the Sun, which act on
the rarefied (select) gases of the higher atmosphere.
The particles are channeled by Earth’s magnetic field,
so auroras are observed mainly near the magnetic poles.
In the Northern Hemisphere they are known as aurora
borealis; in the Southern Hemisphere they are known as
aurora australis.
AIRGLOW
Airglow is similar in origin and nature to the
aurora; it, too, is an upper atmospheric electrical
phenomenon. The main differences between airglow
and aurora are that airglow is quasi-steady (quasi means
seemingly) in appearance, is much fainter than aurora,
and appears in the middle and lower altitudes.
REVIEW QUESTIONS
Q5-12. What is the diameter range of a mature
thunderstorm cell?
Q5-13.
During what stage of a thunderstorm is rain
observed at the surface?
Q5-14.
What is the difference between a macroburst
and a microburst?
Q5-15.
Describe
the
two
different
types
of
thunderstorms?
5-23
