INFERIOR MIRAGE—A spurious image of an
object formed below the true position of that object
by abnormal refractive conditions along the line of
sight; one of the most common of all types of
mirage, and the opposite of a superior mirage.
INSOLATION—(contracted from incoming solar
radiation) In general, solar radiation received at
Earth’s surface.
INSTABILITY—A property of the steady state of a
system
such
that
certain
disturbances
or
perturbations introduced into the steady state will
increase in magnitude, the maximum perturbation
amplitude always remaining larger than the initial
amplitude.
INSTABILITY LINE—Any non-frontal line or band
of convective activity in the atmosphere.
INVERSION—The departure from the usual decrease
or increase with altitude of the value of an
atmospheric property. The layer through which this
departure occurs is known as the inversion layer,
and the lowest altitude at which the departure is
found is known as the base of the inversion. The
term is almost always used in reference to
temperature, but may be applied to moisture and
precipitation.
KATABATIC WIND—Any wind blowing down an
incline; the opposite of anabatic wind. If the wind
is warm, it is called a foehn; if cold, it may be a fall
or gravity wind.
KINETIC ENERGY—The energy that a body
possesses as a consequence of its motion, defined
as the product of one-half of its mass and the square
of its speed, 1/2mv squared.
LAND BREEZE—A coastal breeze blowing from
land to sea, caused by the temperature difference
when the sea surface is warmer than the adjacent
land.
LAPSE RATE—The decrease of an atmospheric
variable
with
height,
the
variable
being
temperature, unless otherwise specified.
LATERAL MIRAGE—A very rare type of mirage in
which the apparent position of an object appears
displaced to one side of its true position.
LIGHT—Visible radiation (about 0.4 to 0.7 micron in
wavelength) considered in terms of its luminous
efficiency.
LOOMING—A
mirage
effect
produced
by
greater-than-normal
refraction
in
the
lower
atmosphere, thus permitting objects to be seen that
are usually below the horizon.
LOW—An “area of low pressure,” refer-ring to a
minimum
of
atmospheric
pressure
in
two
dimensions (closed isobars) on a constant-height
chart or a minimum of height (closed contours) on
a constant-pressure chart. Lows are associated with
cyclonic circulations, and the term is used
interchangeably with cyclone.
MACROCLIMATE—The general large-scale climate
of a large area or country, as distinguished from the
mesoclimate and microclimate.
MAGNETIC NORTH—At any point on Earth’s
surface, the horizontal direction of the Earth’s
magnetic lines of force (direction of a magnetic
meridian) toward the north magnetic pole, i.e., a
direction indicated by the needle of a magnetic
compass. Because of the wide use of the magnetic
compass, magnetic north, rather than TRUE
NORTH, is the common 0° (or 360°) reference in
much of navigational practice, including the
designation of airport runway alignment.
MARITIME
AIR—A
type
of
air
whose
characteristics are developed over an extensive
water surface and which, therefore, has the basic
maritime quality of high moisture content in at least
it's lower levels.
MEAN SEA LEVEL—The average height of the sea
surface, based upon hourly observation of tide
height on the open coast or in adjacent waters
which have free access to the sea. In the United
States, mean sea level is defined as the average
height of the surface of the sea for all stages of the
tide over a 19-year period.
MESOCLIMATE—The climate of small areas of
Earth’s surface that may not be representative of the
general
climate
of
the
district.
The
places
considered in mesoclimatology include small
valleys, “frost hollows,” forest clearings, and open
spaces in towns, all of which may have extremes of
temperature differing by many degrees from those
of adjacent areas. The mesoclimate is intermediate
in
scale
between
the
microclimate
and
microclimate.
MESOPAUSE—The top of the mesosphere.
This
corresponds to the level of minimum temperature at
70 to 80 km.
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