Effect of accumulated energy variation of pelagic tropical cyclones over the Northeast Pacific on El Niño spatial diversity

Abstract

Pelagic tropical cyclones (TCs) over the Northeast Pacific (ENP) do not make landfall, so they have not been paid enough attention. This study explores the impact of these tropical cyclones (TCs) on El Niño diversity, based on both traditional and new classifications of El Niño spatial patterns using accumulated cyclone energy (ACE). The results indicate that when the preceding ENP ACE is strong, it favors the development of eastern-Pacific (EP) El Niño events; conversely, when the preceding ENP ACE is weak, it favors the development of central-Pacific (CP) El Niño events. The modulation of TCs on the low-level wind field is the key process: by influencing the low-level wind field, stronger/weaker ENP ACE induces a stronger reversed Walker circulation anomaly/Walker circulation anomaly and a smaller/larger east-west thermocline gradient. Consequently, the west-to-east transport of warm water over the western Pacific is enhanced/weakened. The center of maximum positive SST anomalies is then located in the equatorial eastern/central Pacific, facilitating the development of the EP/CP El Niño event. Importantly, this feedback is independent of SST persistence. Moreover, in the process of ENP ACE influencing the development of El Niño diversity, Ekman pumping feedback and zonal advection feedback make the largest contributions to the sea water temperature anomaly tendency when the preceding ACE is strong, with thermocline feedback following these two. When the preceding ACE is weak, Ekman pumping feedback is the largest contributor to the sea water temperature anomaly tendency, followed by meridional advection.