APPENDIX I
GLOSSARY
ABSOLUTE INSTABILITY—The state of a column
of air in the atmosphere when it has a
superadiabatic lapse rate of temperature. An air
parcel displaced vertically would be accelerated in
the direction of the displacement.
ABSOLUTE STABILITY—The state of a column of
air in the atmosphere when its lapse rate of
temperature is less than the saturation adiabatic
lapse rate. An air parcel will be denser than its
environment and tend to sink back to its level of
origin.
ADVECTION—The
horizontal
transport
of
an
atmospheric property solely by the mass motion
(velocity field) of the atmosphere.
ADVECTION FOG—Fog caused by the advection of
moist air over a cold surface, and the consequent
cooling of that air to below its dew point.
AIR MASS—A widespread body of air that is
approximately homogeneous in its horizontal
extent, with reference to temperature and moisture.
ANABATIC WIND—An upslope wind; usually
applied only when the wind is blowing up a hill or
mountain as the result of surface heating.
ANTARCTIC FRONT—The semi permanent, semi
continuous front between the Antarctic air of the
Antarctic Continent and the polar air of the
southern oceans; generally comparable to the arctic
front of the Northern Hemisphere.
ANTICYCLOGENESIS—The
strengthening
or
development of an anticyclonic circulation in the
atmosphere.
ANTICYCLOLYSIS—The
weakening
of
an
anticyclonic circulation in the atmosphere.
ANTICYCLONE—A
closed
circulation
in
the
atmosphere that has a clockwise rotation in the
Northern Hemisphere and a counterclockwise
rotation
in
the
Southern
Hemisphere.
Used
inter-changeably with high.
ANTICYCLONIC—Refers to the rotation pattern of
anticyclones. See ANTICYCLONE.
ARCTIC FRONT—The
semi
permanent,
semi
continuous front between the deep, cold arctic air
and the shallower, basically less cold polar air of
northern latitudes; generally comparable to the
Antarctic front of the Southern Hemisphere.
AUTOCONVECTIVE
LAPSE
RATE—The
temperature lapse rate in an atmosphere where
density is constant with height.
BACKING—A change in wind direction in a
counterclockwise
manner
in
the
Northern
Hemisphere and a clockwise manner in the
Southern Hemisphere.
BLOCKING HIGH—An anticyclone that re-mains
stationary or moves slowly westward so as to
effectively block the movement of migratory
cyclones across its latitudes.
BUYS BALLOT’S LAW—The law describing the
relationship
of
horizontal
wind
direction
to
pressure: In the Northern Hemisphere, with your
back to the wind, the lowest pressure will be to your
left; in the Southern Hemisphere, the reverse is
true.
CENTER OF ACTION—Any one of the semi
permanent high or low-pressure systems.
CENTRAL PRESSURE—The atmospheric pressure
at the center of a high or low; the highest pressure in
a high, the lowest in a low.
CHROMOSPHERE—A thin layer of relatively
transparent gases above the photosphere of the Sun.
CLOSED HIGH—A high that is completely encircled
by an isobar or contour line.
CLOSED LOW—A low that is completely encircled
by an isobar or contour line.
COLD-CORE HIGH—Any high that is generally
characterized by colder air near its center than
around its periphery at a given level in the
atmosphere.
COLD-CORE LOW—Any low that is generally
characterized by colder air near its center than
around its periphery at a given level in the
atmosphere.
AI-1
