Tropical climates - The Global Climate System: Patterns, Processes, and Teleconnections - page 69

atmosphere. Burroughs stated that the QBO is ''the most widely observed
feature in [climate] records, and must clearly be regarded as a real feature of
almost all meteorological records'' (Burroughs, 1992, p. 60). For example,
early climatic research identified a statistical link between the QBO and one
of the longest monthly measured European temperature series dating back to
1660. Other researchers have shown that such statistical correlations are
likely linked to variations in pressure (such as the Arctic Oscillation) created
by planetary waves propagated by the QBO.
3.3.2 Tropical influences: surface climate
Because the QBO is centered in the equatorial stratospheric tropics, one
would assume that it should have an effect on the underlying tropospheric
atmosphere. However, one factor potentially limits that interaction; the QBO
does not directly penetrate significantly into the troposphere so any effects
from the QBO are likely to be indirect. For example, although most measure-
ments of the tropical tropospheric temperature do not show a strong oscilla-
tion at the QBO periodicity, some studies have suggested an indirect link
between tropical temperatures and the QBO via a linkage between tropical
stratospheric (QBO) and lower tropospheric winds.
However, given that caveat of a lack of strong physical association,
analysis has shown some climatic indicators of the QBO operating in the
tropics and subtropics. For example, past records of South Asian interannual
monsoon rainfall do display some characteristics of the QBO. Another study
has identified that one of the most prevalent vector-borne diseases in
Australia - Ross River virus - demonstrated a reoccurrence periodicity that
matches the QBO (Done et al. 2002 ). The likely physical mechanism involves
the influence of the QBO on Australian summer rainfall. However, even the
identification of a statistical linkage is particularly useful in that the QBO may
be used as a long-term predictor of the incidence of Ross River virus by public
health authorities.
Other research has shown that precipitation in the tropics displays a strong
QBO periodicity. The summer monsoonal rainfall in India, for example, has
displayed periodicities that suggest an influence by the QBO. Research has
also linked variability in rainfall regimes of other parts of the world to the
stratospheric QBO variations. Scientists have identified in African rainfall
data that negative anomalies in rainfall extend over the central Sahel during
the eastern phase of the QBO.
Many studies have suggested that correlations between tropical precipita-
tion and the QBO might be created by the enhanced deep convection present
during the QBO westward wind shear phase and suppressed when there is
eastward shear in the tropical stratosphere. Such a linkage was recently