The El Nino-Southern Oscillation (ENSO) modulates the frequency of tropical cyclones in some of the global tropical cyclone basins. In fact, the ENSO phenomenon provides the single largest mechanism by which tropical cyclone activity is dramatically altered interseasonally. Although previous studies have identified some of ENSO's effect in various basins, their conclusions were less than comprehensive in that they lacked other important characteristics of tropical cyclones such as changes in intensity, track, longevity, and genesis locations. This paper addresses all of these features and deals specifically with tropical cyclone activity in the North
Pacific and North Atlantic basins.
In the North Pacific, the effect of ENSO is to produce changes in
the strength and position of the monsoon trough. Thus there are expansions and contractions of the favored breeding grounds for tropical cyclones and apparent differences in tracks and intensity. In addition, there is evidence to substantiate a link between the phase of ENSO and intraseasonal variability of some tropical cyclone characteristics. In the North Atlantic, ENSO diminishes tropical cyclone activity and supresses tropical cyclone formation and maintenance at low latitudes. Instead high latitude (many baroclinically-initiated) tropical cyclones tend to flourish