Indian Ocean SST modes and Their Impacts as Simulated in BCC_CSM1.1(m) and HadGEM3

The sea surface temperature anomalies (SSTAs) in the tropical Indian Ocean (TIO) show two dominant modes at interannual time scales, referred to as the Indian Ocean basin mode (IOBM) and dipole mode (IOD). Recent studies have shown that the IOBM and IOD not only affect the local climate, but also induce remarkable influences in East Asia via teleconnections. In this study, we assess simulations of the IOBM and IOD, as well as their teleconnections, using the operational seasonal prediction models from the Met Office (HadGEM3) and Beijing Climate Center [BCC CSM1.1(m)]. It is demonstrated that the spatial patterns and seasonal cycles are generally reproduced by the control simulations of BCC CSM1.1(m) and HadGEM3, although spectra biases exist. The relationship between the TIO SSTA and El Nino is successfully simulated by both models, including the persistent IOBM warming following El Nino and the IOD–El Nino interactions. BCC CSM1.1(m) and HadGEM3 are capable of simulating the observed local impact of the IOBM, such as the strengthening of the South Asian high. The influences of the IOBM on Yangtze River rainfall are also captured well by both models, although this teleconnection is slightly weaker in BCC CSM1.1(m) due to the underestimation of the northwestern Pacific subtropical high. The local effect of the IOD on East African rainfall is reproduced by both models. However, the remote control of the IOD on rainfall over southwestern China is not clear in either model. It is shown that the realistic simulations of TIO SST modes and their teleconnections give rise to the source of skillful seasonal predictions over China.