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front |
Generally, the interface or transition
zone between two air masses of different density.
Since the temperature distribution is the most important regulator of
atmospheric density, a front almost invariably separates air masses of
different temperature. Along with the basic density criterion and the
common temperature criterion, many other features may distinguish a front,
such as a pressure trough, a change in wind direction, a moisture discontinuity,
and certain characteristic cloud and precipitation forms. The term front
is used ambiguously for: a frontal zone, the three-dimensional zone or
layer of large horizontal density gradient, bounded by frontal surfaces
across which the horizontal density gradient is discontinuous (frontal
surface usually refers specifically to the warmer side of the frontal
zone); and a surface front, the line of intersection of a frontal surface
or frontal zone with the earth's surface or less frequently, with a specified
constant pressure surface. |
