The fidelity of the eight Asia-Pacific Economic Cooperation (APEC) Climate Center (APCC) models in representing the inter-annual variability and decadal shift in the northeast monsoon (NEM; October–December) rainfall over Southern Peninsular India (SPI) is evaluated. The hindcast data is used for the period of 28 years from 1983 to 2010 based on September initial conditions. The observations showed a clear inter-annual and inter-decadal variability of NEM rainfall during the study period. The analysis suggests that most of the models exhibited poor skill in representing the inter-annual variability. Only APCC model rainfall is in phase with observed SPI rainfall variations on the inter-annual time scale. It is noticed from the observed NEM rainfall time series that the period 1990–1999 (first decade) displays an above-normal rainfall and the period 2000–2010 (second decade) displays a below normal rainfall over the SPI region. It is also evident from the observations that NEM rainfall for most of the years displayed negative anomalies in the second decade including El Niño and La Niña years, while in the first decade positive anomalies are noted, suggesting the presence of decadal variability in the NEM. Rainfall variations in most of the coupled models are in phase with the observations during the second decade but are out of phase during the first decade. As evidenced from the observations that the intensified deep convection over the Indo-western Pacific region results in too far southward movement of the intertropical convergence zone (ITCZ) during the second decade. The southward shift in the strong upper-level divergence associated with lower-level convergence over the south Indian Ocean caused negative rainfall anomalies over the SPI in this decade. Further, the difference between the second and first decade demonstrates that an anomalous anticyclonic circulation over the Indian subcontinent is accountable for the vigorous dry northerly flow towards the SPI region and the resultant decadal shift in the rainfall pattern. Though the southward shift in the rainfall and large-scale circulation patterns are mildly captured by some models from decade to decade, most of the models completely misrepresented it. This study suggests that the coupled models displayed a very limited skill not only in capturing the inter-annual variability but also in representing the decadal variability of NEM rainfall.

评估了八种亚太经济合作组织（APEC）气候中心（APCC）模型的保真度，这些模型代表了印度南部半岛（SPI）东北季风（NEM； 10月至12月）降水的年际变化和年代际变化。 。根据9月份的初始条件，后播数据用于1983年至2010年的28年期间。观测结果表明，在研究期间，NEM降水具有明显的年际和年代际变化。分析表明，大多数模型在表示年际变异性方面表现出较差的技巧。在年际尺度上，只有APCC模型降雨与观测到的SPI降雨变化同相。从观测到的NEM降雨时间序列中可以看出，在SPI地区，1990-1999年（第一个十年）的降雨量高于正常水平，而2000-2010年（第二个十年）的降雨量低于正常水平。从观察结果还可以明显看出，在大多数年份，NEM的降雨量在第二个十年（包括厄尔尼诺和拉尼娜年）都显示出负异常，而在最初的十年中，出现了正异常，表明NEM存在年代际变率。在大多数耦合模型中，降雨变化与第二个十年的观测值是一致的，但在第一个十年中是不同步的。从观察中可以看出，印度洋-西太平洋地区上空的强烈对流加剧，导致第二个十年间热带辐合带（ITCZ）向南运动太远。南印度洋上空高层辐合强烈的南移与下层辐合有关，在本十年中造成了SPI的负降雨异常。此外，第二个十年与第一个十年之间的差异表明，印度次大陆上反气旋环流异常是造成朝着SPI地区的强烈北风向北流动以及由此导致的降雨格局年代际变化的原因。尽管某些模型在十年到十年间温和地记录了降雨的南移和大规模的环流模式，大多数模型完全歪曲了它。这项研究表明，耦合模型不仅在捕获年际变化方面表现出非常有限的技能，而且在表示NEM降雨的年代际变化方面也表现出非常有限的技能。