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.