Early and Extreme Warming in the South China Sea During 2015/2016: Role of an Unusual Indian Ocean Dipole Event

Abstract

The South China Sea (SCS) experienced sea surface temperature that broke historical records in the autumn of 2015. This event cannot be explained by El Niño alone because the SCS usually warms during the El Niño peak and decaying phases. We show that an early anomalous anticyclone (AAC) establishment over the SCS in August contributed to this early warming. Analysis and simple modeling results reveal that such an early AAC establishment could be interpreted as a direct Rossby wave response to a cooling anomaly over the Maritime Continent (MC) and a Kelvin wave response to a heating anomaly over the tropical Indian Ocean (TIO). An unusual Indian Ocean dipole event contributed to the atmospheric heating anomaly over the TIO and made the cooling anomaly shrink to MC region. We should take into consideration the Indian Ocean SST patterns to improve the predictability of extreme East Asian climate.

Plain Language Summary

Multiple data sets suggest that the sea surface temperature (SST) in the SCS in the boreal autumn of 2015 broke the historical record dating back over 140 years. This warm event caused severe coral bleaching on Dongsha Atoll. The highest SST was 1.15°C and 0.98°C warmer than those in the autumns of 1982 and 1997, respectively. In contrast to the 1982 and 1997 super El Niño events, we found that the SCS began to warm rapidly in August 2015, which was earlier than in 1982 and 1997. Our analyses show that this obvious difference could be attributed to the early establishment of an anomalous SCS anticyclonic flow that warmed the surface water through solar radiation and oceanic advection. Observational and modeling results indicate that the early establishment of anomalous SCS anticyclonic flow could be largely attributed to anomalous SST patterns induced by an unusual Indian Ocean dipole during 2015/2016. Understanding the mechanisms of extremely warm events could be helpful for predicting extreme climate events and understanding the marine environmental changes.