LAUSR

The East Asia–Pacific (EAP) teleconnection pattern is the dominant mode of circulation variability during boreal summer over the western North Pacific and East Asia, extending from the tropics to high latitudes. However, much of this pattern is absent in multi-model ensemble mean forecasts, characterized by very weak circulation anomalies in the mid and high latitudes. This study focuses on the absence of the EAP pattern in the extratropics, using state-of-the-art coupled seasonal forecast systems. The results indicate that the extratropical circulation is much less predictable, and lies in the large spread among different ensemble members, implying a large contribution from atmospheric internal variability. However, the tropical–mid-latitude teleconnections are also relatively weaker in models than observations, which also contributes to the failure of prediction of the extratropical circulation. Further results indicate that the extratropical EAP pattern varies closely with the anomalous surface temperatures in eastern Russia, which also show low predictability. This unpredictable circulation–surface temperature connection associated with the EAP pattern can also modulate the East Asian rainband.摘要东亚-太平洋遥相关型(EAP型)是西北太平洋-东亚地区夏季环流变化的主要模态, 其结构范围从热带延伸至中高纬度地区. 然而, 在多模式集合平均预报中, EAP型没有出现, 其中高纬度地区环流异常非常弱. 本文利用现阶段较先进的季度预测系统, 分析了预测系统无法预测出EAP型热带外分量的原因. 结果表明, EAP型的热带外环流可预测性较低, 主要由于模式不同积分成员之间存在非常大的离散度, 受大气内部变率的影响. 另一方面, 模式所预测的EAP型的经向联系相对于观测较弱, 这也导致了模式无法预测出该遥相关型的热带外分量. 进一步的研究发现, EAP型的热带外分量与俄罗斯东部地区表面温度异常的变化紧密联系, 后者的可预测性也较低. 与EAP型相联系的这种环流-表面温度的不可预测性也将调制东亚降水雨带的变化.