2008 REED’s East Coast Edition - Weather
prevail in the low-latitude cell, while in the This entire pattern tends to shift north and
mid-latitude cell, westerly breezes prevail. south with seasonal changes (see Figure 1).
Figure 1 Worldwide weather systems are dictated by the three distinct circulating cells in op-
eration in the respective hemispheres, with separate prevailing wind patterns along specific
bands of latitude in each. These in turn are influenced by the Earth’s rotation, which creates
the Coriolis effect.
To complicate matters further, this prevail- advancing. Differing types of weather typi-
ing pressure and wind pattern is subject to cally form along these frontal boundaries.
interruption, especially in the temperate,
Air Mass Weather
mid-latitude region. A variety of factors
there contribute to the frequent formation
Air masses often cover large areas of the
of transient high- and low-pressure systems
earth’s surface with huge domes of air having
that generally sweep eastward through the
fairly homogeneous temperature and hu-
region. Because of the Coriolis effect, in the
midity. They derive their character from the
Northern Hemisphere winds tend to swirl
region where they’re formed: Those formed
clockwise around high-pressure centers and
over polar land regions tend to be cold and
counterclockwise around lows. This temper-
dry, for example; those over tropical water
ate region is also a common meeting place of
are likely to be warm and moist.
warm air masses formed in lower latitudes
When air masses migrate away from their
and cold air masses formed in higher lati-
source region—which they often do—the
tudes. The weather within each type of air
weather associated with them is determined
mass has distinctly different characteristics.
not only by their moisture and heat content,
Fronts form at the boundary between differ-
but also by the contrast in temperature be-
ing air masses—cold fronts where the cold
tween the air and the surface they’re passing
air mass is advancing on the warm mass, and
over. The designation of an air mass as cold
warm fronts where the relatively warm air is
or warm is taken from the air’s temperature
in relation to surface temperature.
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