Tropical climates - The Global Climate System: Patterns, Processes, and Teleconnections - page 71

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Figure 3.6 Time series of
equatorial ozone anomalies
in Dobson units (solid line)
with a reference QBO wind
time series (dashed line)
based in part on Singapore
stratospheric winds.
(Adapted from Randel and
Wu 1996 : permission from
American Meteorological
Society)

10

0

-10

-20

79 83 87

YEAR

91 95

SBUV + SBUV/2

SAGE II QBO time series

(descent) in the subtropics associated with the westerly (easterly) wind shear
phase. However, in addition to the QBO, ozone also displays an annual cycle
that modulates the fundamental periodicity of ozone to some extent.
Given the initial identification of one of the QBO phases by plume move-
ment from the volcano Krakatoa, it is not surprising that QBO variability is
evident in records of trace atmospheric substances such as volcanic aerosols,
as well as water vapor and methane. Researchers have illustrated markedly
different aerosol spatial distributions from equatorial volcanic eruptions as
a function of the phase of the QBO. Similar findings have been reported for
water vapor, methane, and nitrates concentrations.

3.3.4 Tropical influences: tropical cyclones
One of the strongest apparent linkages between the QBO and the tropical
atmosphere is the association between stratospheric winds and tropical
cyclone activity in the Northern Hemispheric Atlantic Ocean. William Gray
revealed one of the first analyses of a relationship between tropical storm
frequency (in this case, the number of hurricane days per season) and the
QBO in 1984 (Figure 3.7 ). Analyzing a variety of hurricane parameters, he
determined that the QBO exerts the strongest influence on the minimum sea
surface pressure anomalies of hurricanes such that overall summer sea level
pressure in the Caribbean averages 0.21 millibars lower under the western phase
of the QBO as opposed to the eastern phase. Subsequently, Gray and his
colleagues incorporated the QBO as a primary variable in their statistical scheme
for forecasting seasonal tropical storm activity. Fundamentally, they have