Impact of ENSO on the South China Sea during ENSO decaying winter–spring modeled by a regional coupled model (a new mesoscale perspective)

Abstract

Studies have suggested that the ocean dynamics in the South China Sea (SCS) play a crucial role in local air–sea processes and the regional weather or climate system. We used a high-resolution regional coupled model to investigate the impact of the El Niño Southern Oscillation (ENSO) on the atmospheric and oceanic processes in the SCS during ENSO decaying winter–spring. The coupled model demonstrates the important roles of mesoscale features in the regional air–sea interaction induced by the anomalous ENSO conditions. During El Niño, the Kuroshio intrusion into the SCS is enhanced which further modifies the upper and middle layer circulation of the SCS. The reduced planetary vorticity transport during El Niño results in a weakened cyclonic circulation and thinner mixed layer in the southern SCS. The modulations of the cyclonic circulation in the southern SCS, Vietnam offshore jet, and the coastal current during ENSO event enhance oceanic advection that favors an ocean-forcing energy exchange to the atmosphere across the air–sea interface. The relative importance of atmospheric and oceanic forcing on the SST change during the ENSO evolution is verified using a heat budget analysis for different regions of SCS. In the El Niño following spring, the advective term due to anomalous Ekman drift dominates the cooling process in the northern and eastern SCS. These thermal structure changes in the SCS are contributed by the wind–current–topography interactions.