Contrasting Impacts of Two Types of El Niño on Interannual Variations of Marine Heatwaves in the South China Sea

Abstract

This study utilizes multiple observational and reanalysis data sets to investigate the contrasting effects of Eastern Pacific (EP) and Central Pacific (CP) El Niño on interannual variations of marine heatwaves (MHWs) in the South China Sea (SCS) from the developing autumn to decaying summer of El Niño. EP El Niño is associated with more frequent, intense, and prolonged MHWs throughout its life cycle, while CP El Niño is linked to a general decrease in MHW characteristics, except in decaying summer. During EP El Niño, an anomalous anticyclone over the SCS during developing autumn induces warming mainly by increasing shortwave radiation and diminishing latent heat release, fostering MHW development. The anomalous warming persists into decaying summer, intensified by the influence of an anticyclone associated with the western North Pacific subtropical high (WNPSH). Reduced MHWs during CP El Niño are primarily attributed to cooling in developing autumn and early cessation of warming in decaying summer. This autumn cooling is connected to enhanced latent heat release, anomalous Ekman upwelling, and negative horizontal advection caused by an anomalous cyclone around the SCS. The early fade of summer warming in CP El Niño is due to the northeastward shift of the WNPSH compared to the EP El Niño scenario, which reduces its ability to warm the SCS. The sea surface temperature (SST) evolutions during CP El Niño events highlight the thermal status of developing autumn and decaying summer as critical factors for MHW occurrence and persistence, underscoring the necessity to assess the thermal state preceding SST increases in MHW research.