Different controls of tropical cyclone activity in the Eastern Pacific for two types of El Niño

Abstract

Abstract The El Niño–Southern Oscillation (ENSO) is known to have different modes of expression, characterized by different dynamics and spatial anomalies patterns: the Eastern Pacific (EP) and Central Pacific (CP) El Niño. The main region of influence of the former is located in the Eastern Pacific, while CP events have a stronger signature of ocean/climate anomalies in the Central West Pacific. This leads to distinctive oceanic and atmospheric signatures that likely have different influences on tropical cyclone (TC) activity in the Eastern Pacific, the second most active region in the world. In this study we investigate the respective role of oceanic and atmospheric conditions on TC formation and intensification in the Eastern Pacific associated with these two flavors of ENSO. We find that the oceanic control, through meridional redistribution of subsurface heat, is the main driver of TC activity during the hurricane season following EP events. In contrast, atmospheric conditions tend to be destructive to TC intensification after those events. The altered atmospheric circulation, in particular the reduction of vertical wind shear and the increase in relative humidity, tends to be more influential in controlling TC activity post CP events. However, unlike for subsurface heat, these changes in atmospheric conditions are not statistically distinct between these two ENSO flavors—although they are consistent across all atmospheric data sets tested. Overall, unlike after EP El Niño events, the hurricane season activity following a CP event is not significantly different from neutral or even La Niña years.