Subj : Wx Terms (A)(4)
To   : All
From : Daryl Stout
Date : Thu Nov 02 2017 12:07 am

Angle of Reflection
The angle at which a reflected ray of energy leaves a reflecting surface.
It is measured between the outgoing ray and a perpendicular to the
surface at the point of incidence (i.e., where the ray strikes).

Angstrom
A unit of length equal to 10-8 cm.

Annual Flood
In hydrologic terms, the maximum discharge peak during a given water
year (October 1 - September 30).

Anomaly
The deviation of a measurable unit (e.g., temperature or precipitation)
over a period in a given region from the long-term average, often the
thirty-year mean, for that region.

Antedecent Precipitation Index
(Abbrev. API) - an index of moisture stored within a drainage basin
before a storm.

Anthelion
A luminous white spot that appears on the parhelic circle at the same
altitude as the sun and 180� from it in azimuth.

Anthropogenic Source
A pollutant source caused or produced by humans.

Anti-wind
The upper or return branch of an along-valley wind system, as confined
within a valley, and blowing in a direction opposite to the winds in the
lower altitudes of the valley.

Anticyclogenesis
The formation or intensification of an anticyclone or high pressure
center.

Anticyclone
A large-scale circulation of winds around a central region of high
atmospheric pressure, clockwise in the Northern Hemisphere,
counterclockwise in the Southern Hemisphere

Anticyclonic Rotation
Rotation in the opposite sense as the Earth's rotation, i.e., clockwise
in the Northern Hemisphere as would be seen from above. The opposite of
cyclonic rotation.

Antilles Current
A current which originates in the vicinity of the Leeward Islands as
part of the Atlantic North Equatorial Current.

Anvil
The flat, spreading top of a cumulonimbus cloud, often shaped like an
anvil. Thunderstorm anvils may spread hundreds of miles downwind from
the thunderstorm itself, and sometimes may spread upwind.

Anvil Crawler
[Slang], a lightning discharge occurring within the anvil of a
thunderstorm, characterized by one or more channels that appear to
crawl along the underside of the anvil. They typically appear during the
weakening or dissipating stage of the parent thunderstorm, or during an
active MCS.

Anvil Dome
A large overshooting top or penetrating top.

Anvil Rollover
Slang for a circular or semicircular lip of clouds along the underside
of the upwind part of a back-sheared anvil, indicating rapid expansion
of the anvil.

Anvil Zits
Slang for frequent (often continuous or nearly continuous), localized
lightning discharges occurring from within a thunderstorm anvil.

AO
Arctic Oscillation - the Arctic Oscillation is a pattern in which
atmospheric pressure at polar and middle latitudes fluctuates between
negative and positive phases. The negative phase brings higher-than-normal
pressure over the polar region and lower-than-normal pressure at about
45� north latitude. The negative phase allows cold air to plunge
into the Midwestern United States and western Europe, and storms bring
rain to the Mediterranean. The positive phase brings the opposite
conditions, steering ocean storms farther north and bringing wetter
weather to Alaska, Scotland and Scandinavia and drier conditions to
areas such as California, Spain and the Middle East. In recent years
research has shown, the Arctic Oscillation has been mostly in its
positive phase. Some researchers argue that the North Atlantic
Oscillation is in fact part of the AO.

AOA
At or above

AOB
At or below

AOPA
Aircraft Owners and Pilots Association

AP
Anomalous Propagation. Radar term for false (non-precipitation) echoes
resulting from nonstandard propagation of the radar beam under certain
atmospheric conditions. Sometimes referred to as "ground clutter".

AP Index
In solar-terrestrial terms, an averaged planetary A Index based on data
from a set of specific stations.

APD
On a buoy report, the average wave period (seconds) of all waves during
the 20-minute period.

Aphelion
The point on the annual orbit of a body (about the sun) that is farthest
from the sun; at present, the earth reaches this point (152 million
kilometer from the sun) on about 5 July. Opposite of perihelion.

API Method
In hydrologic terms, a statistical method to estimate the amount of
surface runoff which will occur from a basin from a given rainstorm
based on the antecedent precipitation index, physical characteristics of
the basin, time of year, storm duration, rainfall amount, and rainfall
intensity.

Apogee
The farthest distance between the moon and earth or the earth and sun.

Apparent Temperature
A measure of human discomfort due to combined heat and humidity (e.g.,
heat index).

Apparent Wind
The speed and true direction from which the wind appears to blow with
reference to a moving point. Sometimes called RELATIVE WIND.

APRCH
Approach

APRCHG
approaching

APRNT
apparent

APST
Aviation Products and Services Team

Aquiclude
In hydrologic terms, a formation which contains water but cannot transmit
it rapidly enough to furnish a significant supply to a well or spring.

Aquifer
In hydrologic terms, permeable layers of underground rock, or sand that
hold or transmit groundwater below the water table that will yield water
to a well in sufficient quantities to produce water for beneficial use.

Aquifuge
In hydrologic terms, a geologic formation which has no interconnected
openings and cannot hold or transmit water.

ARAM
Aviation, Range, and Aerospace Meteorology

Arch Dam
A concrete arch dam is used in sites where the ratio of width between
abutments to height is not great and where the foundation at the
abutments is solid rock capable of resisting great forces. The arch
provides resistance to movement. When combined with the weight of
concrete (arch-gravity dam), both the weight and shape of the structure
provide great resistance to the pressure of water.

Arch Filament System (AFS)
In solar-terrestrial terms, a bright, compact plage crossed by a system
of small, arched filaments, which is often a sign of rapid or continued
growth in an Active Region.

Arctic
The region within the Arctic Circle, or, loosely, northern regions in
general, characterized by very low temperatures.

Arctic front
The boundary or front separating deep, cold arctic air from shallower,
relatively less cold polar air.

Arctic Oscillation
(abbrev. AO)- The Arctic Oscillation is a pattern in which atmospheric
pressure at polar and middle latitudes fluctuates between negative and
positive phases. The negative phase brings higher-than-normal pressure
over the polar region and lower-than-normal pressure at about 45�
north latitude. The negative phase allows cold air to plunge into the
Midwestern United States and western Europe, and storms bring rain to
the Mediterranean. The positive phase brings the opposite conditions,
steering ocean storms farther north and bringing wetter weather to
Alaska, Scotland and Scandinavia and drier conditions to areas such as
California, Spain and the Middle East. In recent years research has
shown, the Arctic Oscillation has been mostly in its positive phase.
Some researchers argue that the North Atlantic Oscillation is in fact
part of the AO.



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