LATERAL MIRAGE.—Since the positions of
above and below represent superior and inferior
mirages respectively, the lateral mirage then appears to
the side of the object being viewed.
Looming
Looming is similar to a mirage in that it brings into
view objects that are over a distant horizon. Looming
occurs when there is superrefraction in the lower
atmosphere, which makes reflected light travel a path
similar to the curvature of Earth. Objects over the
horizon may be seen when light reflected from them
takes this path. Looming is somewhat rare and is
normally observed over flat surfaces, such as oceans
and deserts.
Scintillation
Scintillation is caused by variations in atmospheric
density near the horizon. It produces the appearance of
rapid changes in the position, brightness, and color of
distinct luminous objects, such as stars. Stars flickering
and changing color near the horizon shortly after sunset
are good examples of scintillation and are a reasonably
common phenomenon.
Crepuscular Rays
Crepuscular rays are another common phenomena.
They are simply sunbeams that are rendered luminous
by haze and dust particles suspended in the atmosphere.
They are seen before and after sunrise and sunset as
they pass through small breaks or openings in or around
clouds. The sunbeams are actually parallel but appear
to diverge from the Sun.
REVIEW QUESTIONS
Q5-8.
Name the two sources of light.
Q5-9.
What is the difference between natural and
artificial light?
Q5-10.
What is the difference between reflection and
refraction?
Q5-11. What is a mirage?
ELECTROMETEORS
LEARNING
OBJECTIVE:
Identify
the
characteristics
of
electrometeors
(thunderstorms,
lightning,
auroras,
and
airglow).
An
electrometeor
is
a
visible
or
audible
manifestation of atmospheric electricity. The more
important electrometeors are thunderstorms, lightning,
and auroras.
THUNDERSTORMS
The thunderstorm represents one of the most
formidable weather hazards in temperate and tropical
zones. Though the effects of the thunderstorm tend to
be localized, the turbulence, high winds, heavy rain,
and occasional hail accompanying the thunderstorm are
a definite threat to the safety of flight operations and to
the security of naval installations. The Aerographer’s
Mate must be acquainted with the structure of
thunderstorms and the types of weather associated with
them.
Formation
The
thunderstorm
represents
a
violent
and
spectacular
atmospheric
phenomenon.
Lightning,
thunder, heavy rain, gusty surface wind, and frequent
hail usually accompany it. A certain combination of
atmospheric conditions is necessary for the formation
of a thunderstorm. These factors are conditionally
unstable air of relatively high humidity and some type
of lifting action. Before the air actually becomes
unstable, it must be lifted to a point where it is warmer
than the surrounding air. When this condition is brought
about, the relatively warmer air continues to rise freely
until, at some point aloft, its temperature has cooled to
the temperature of the surrounding air. Some type of
external lifting action must be introduced in order to
raise the warm surface air to a point where it can rise
freely. Many conditions satisfy this requirement;
heating, terrain, fronts, or convergence may lift an air
mass.
Structure
The
fundamental
structural
element
of
the
thunderstorm is the unit of convective circulation
known as the convective cell. A mature thunderstorm
contains several of these cells, which vary in diameter
from 1 to 6 miles. By radar analysis and measurement
of drafts, it has been determined that, generally, each
cell is independent of surrounding cells of the same
storm. Each cell progresses through a cycle, which lasts
from 1 to 3 hours. In the initial stage (cumulus
development), the cloud consists of a single cell, but as
the development progresses, new cells form and older
cells dissipate. The life cycle of the thunderstorm cell
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