troposphere and stratosphere, usually characterized
by an abrupt change of lapse rate.
atmosphere extending from the surface to the
tropopause; that is, the lowest 10 to 20 km of the
TROUGHAn elongated area of low atmospheric
pressure; the opposite of a ridge.
TRUE NORTHThe direction from any point on
Earths surface toward the geographic North Pole;
the northerly direction along any projection of
Earths axis upon Earths surface, for example,
along a longitude line. Except for much of
navigational practice (which uses magnetic north),
true north is the universal 0° (or 360°, mapping
UPSTREAMIn the direction from which a fluid is
UPWINDIn the direction from which the wind is
VECTORAny quantity, such as force, velocity, or
acceleration, that has both magnitude and direction
at each point in space, as opposed to a scalar, which
represented by an arrow of length proportional to
its magnitude, pointing in the assigned direction.
VEERINGA change in wind direction in a
clockwise sense in the Northern Hemisphere and
VERNAL EQUINOXFor either hemisphere, the
equinox at which the Suns most direct rays
northern latitudes, this occurs approximately on 21
March; the Suns most direct rays are centered over
the equator and moving north.
VIRTUAL TEMPERATUREIn a system of moist
air, the temperature of dry air having the same
density and pressure as the moist air. It is always
greater than the actual temperature.
WARM-CORE HIGHAt a given level in the
atmosphere, any high that is warmer at its center
than at its periphery.
WARM-CORE LOWAt a given level in the
atmosphere, any low that is warmer at its center
than at its periphery.
WARM FRONTAny non-occluded front or portion
thereof that moves in such a way that warmer air
replaces colder air.
WARM SECTORThat area within the circulation of
a wave cyclone where the warm air is found. It lies
between the cold front and the warm front of the
storm; and, in the typical case, the warm sector
continually diminishes in size and ultimately
disappears (at the surface) as the result of
WAVE CYCLONEA cyclone that forms and moves
along a front.
WAVE THEORY OF CYCLONESA theory of
cyclone development based upon the principles of
wave formation on an interface between two fluids.
In the atmosphere, a front is taken as such an
WEATHERThe state of the atmosphere, mainly
with respect to its effect upon life and human
westerlies, midlatitude westerlies, polar westerlies,
temperate westerlies, zonal westerlies, and zonal
winds) Specifically, the dominant west-to-east
motion of the atmosphere, centered over the middle
latitudes of both hemispheres. At the surface, the
westerly belt extends, on the average, from about
35° to 65° latitude. At upper levels, the westerlies
extend farther equatorward and poleward. The
equatorward boundary is fairly well defined by the
boundary is quite diffuse and variable.
WIND-CHILL FACTORThe cooling effect of any
combination of temperature and wind, expressed as
the loss of body heat, in kilogram calories per hour
per square meter of skin surface. The wind-chill:
factor. is based on the cooling rate of a nude body in
the shade; It is only an approximation, because of
individual body variations in shape, size, and