Geoscience Reference
In-Depth Information
11
CHAPTER ELEVEN
Tropical weather
and climate
LEARNING OBJECTIVES
When you have read this chapter you will:
n
understand the characteristics and significance of the intertropical convergence zone
n
be familiar with the principal weather systems that occur in low latitudes and their distribution
n
know some of the diurnal and local effects that influence tropical weather
n
know where and how tropical cyclones tend to occur
n
understand the basic mechanisms and characteristics of El Niño and La Niña events
Tropical climates are of especial geographical
interest because 50 percent of the surface of the
globe lies between latitudes 30
Asia, but only to 20
N in West Africa, while in late
summer and autumn tropical hurricanes may
affect 'extra-tropical' areas of East Asia and eastern
North America. Not only do the tropical margins
extend seasonally poleward, but in the zone
between the major subtropical high pressure cells
there is frequent interaction between temperate
and tropical disturbances. Elsewhere and on other
occasions, distinct tropical and mid-latitude
storms are observed. In general, however, the
tropical atmosphere is far from being a discrete
entity and any meteorological or climatological
boundaries must be arbitrary. There are,
nevertheless, a number of distinctive features of
tropical weather, as discussed below.
Several basic factors help to shape tropical
weather processes and also affect their analysis
and interpretation. First, the Coriolis parameter
approaches zero at the equator, so that winds may
depart considerably from geostrophic balance.
°
S, and
over 75 percent of the world's population
inhabit climatically tropical lands. This chapter
first describes the Trade Wind systems, the
intertropical convergence zone and tropical
weather systems. The major monsoon regimes
are then examined and the climate of Amazonia.
The effects of the alternating phases of the El
Niño-Southern Oscillation in the equatorial
Pacific Ocean is discussed as well as other causes
of climatic variation in the tropics. Finally, the
problems of forecasting tropical weather are
briefly considered.
The latitudinal limits of tropical climates vary
greatly with longitude and season, and tropical
weather conditions may reach well beyond the
Tropics of Cancer and Capricorn. For example,
the summer monsoon extends to 30°N in South
°
N and 30
°
