ABSTRACT
The relationship between tropical cyclones of the Western
Pacific and Indian oceans and the Madden-Julian oscillation
Brant
Liebmann
Cooperative Institute for Research in Environmental Sciences,
University of Colorado, Boulder
Harry H. Hendon
Program in Atmospheric and Oceanic Sciences and Cooperative
Institute for Research in Environmental Sciences, University
of Colorado, Boulder
John D. Glick
Cooperative Institute for Research in Environmental Sciences,
University of Colorado, Boulder
Abstract
We document a relationship between tropical cyclones
of the Indian and western
Pacific oceans and the Madden-Julian
Oscillation (MJO). Cyclones preferentially
occur during the convective phase of the oscillation,
and cluster around the
low-level cyclonic vorticity and divergence anomalies
that appear poleward and
westward of the large-scale convective
anomaly associated with the MJO.
Although the absolute numbers of storms and
typhoons are enhanced during the
convective phase of the oscillation,
the ratio of storms and typhoons formed per
depression is the same in the convective
phase as the dry phase of the
oscillation. There exist more storms and
typhoons simply by there being more
depressions in the convective phase.
The third result of this study is that the
increase in cyclone activity during
active periods of convection is not restricted
to MJO activity. In fact, we
find that an equal increase occurs during the convective
phase of an arbitrarily
chosen, completely independent band from the
MJO. We conclude that the MJO does
not influence tropical cyclones in a unique
fashion, but it is important because
of the relatively large proportion of tropical
variance that is explained by it.