Appendix A: Air Masses and Frontal Zones
A body of air in which the temperature and
moisture are fairly uniform over a large area
is known as an air mass. The boundary
between a given air mass and its neighbor is
usually sharply defined. This discontinuity is
termed a front. In the convergence zone
between the tropical polar air masses, winds
are variable and high, and accompanied by
stormy weather. This zone is called the
polar front. A large number of the Earth’s
cyclonic storms are generated here. The
properties of an air mass are derived partly
from the regions over which it passes. Those
land or ocean surfaces that strongly impress
their characteristics on the overlying air masses
are called source regions. Air masses are classified according to their latitudinal position
(which determines thermal properties), and
underlying surface, whether continent or ocean
(determining moisture content). They are
summarized in Table 1 and illustrated in Fig. 1.
R.G. Bailey, Ecoregions, DOI 10.1007/978-1-4939-0524-9, # Springer Science+Media, LLC 2014
141