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

Abstract

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 Niño is successfully simulated by both models, including the persistent IOBM warming following El Niño and the IOD–El Niño 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.

摘要

年际尺度上印度洋海温变化主要呈现出两个主要模态: 洋盆一致模态(IOBM)以及偶极子模态(IOD). 最近的研究发现, IOBM和IOD模态不仅能带来印度洋局地的气候异常, 还能通过遥相关影响东亚气候. 本研究针对中国气象局和英国气象局的气候预测业务模式(分别为BCC_CSM1.1(m)和HadGEM3), 评估其对印度洋海温主模态及其遥相关特征的模拟能力. 评估结果显示, 两家模式能够把握住印度洋海温主要模态的基本特征(例如空间分布型、季节循环等), 然而一些模拟偏差(例如频谱等)依然存在. 观测中印度洋海温与El Niño的关系(例如El Niño衰弱期印度洋海温的增暖, 以及IOD-El Niño相互作用等)在两家模式中都有一定的体现. BCC_CSM1.1(m) 和HadGEM3都能模拟出IOBM的局地效应(例如南亚高压的增强), 同时长江流域夏季降水对IOBM的遥相关响应也在两家模式里有所反映, 受限于西北太平洋反气旋响应的偏弱, BCC_CSM1.1(m)中长江流域夏季降水的响应也略偏小. BCC_CSM1.1(m) 和HadGEM3能很好地重现IOD对环印度洋地区的气候影响, 然而观测中我国西南降水对IOD的响应在两家模式中均未有体现. 同时, 我们的研究也表明了印度洋海温及其遥相关影响的模拟水平对我国季节气候预测至关重要.