Tropical climates - The Global Climate System: Patterns, Processes, and Teleconnections - page 67

the equator towards the Southern Hemisphere continents, picking up moisture
from the warm tropical oceans to become the wet monsoon over north Australia.
The southwestern part of North America is also monsoonal. Here the surface
zonal wind changes from an easterly in January to westerly in July and there is an
increase in rainfall over large areas of southwestern North America and southern
Mexico from June to July. Recent data suggest a summer monsoon circulation
over the subtropical South American highlands with distinct rainfall summer
increases over the central Andes and the southern parts and north coast of Brazil.
The complexities of the monsoon circulation systems, as already noted, are
described in Chapter 9 . Further excellent descriptions may be found in the works
of Das (Das 1986 , 2002 ).
3.3 ESSAY: The Quasi-biennial Oscillation and tropical
climate variations
Randall Cerveny, Arizona State University
The Quasi-biennial Oscillation (QBO) is a tropical atmospheric phenomenon
evidenced by a reversal in the stratospheric wind direction near the equator
approximately every 28 months. It is an unusual phenomenon that researchers
now postulate arises from an interaction of propagating waves in a rotating
stratified atmosphere. The interactions of these waves produce oscillatory
perturbations that fundamentally modify the extratropical tropospheric cir-
culation and consequently their climates and that of the globe as a whole. A
wide variety of climate records around the world demonstrate periodicities
that appear to be well correlated with the QBO. With regard to this essay,
much research has recently been published indicating that the QBO also
exerts a strong influence on the tropics of the Earth - and even other planets!
For a brief history and discussion of QBO observations and theory, please see
the discussion in Chapter 2 . In this essay, I address the impact of the QBO on
climate variability in the tropics, including the controls on seasonal hurricane
and tropical storm development, the Southern Oscillation and even the
planetary length of day.
3.3.1 Planetary concerns
Although terrestrial observations of features associated with the QBO have
been made for the last 120 years (dating back to the eruption of Krakatoa in
the East Indies), only recently have scientists identified QBO-like pheno-
mena on other planets, such as the planet Jupiter. Recent information from a
Jovian space probe (Flasar et al. 2004 ) identified intense (140 m s 1 ) high-
altitude equatorial winds from measurements of the infrared spectra of
Jupiter's stratosphere (Figure 3.5 ). This jet apparently has many of the