The Warm Arctic—Cold Eurasia Pattern and Its Key Region in Winter in CMIP6 Model Simulations

Abstract

An enhanced Warm Arctic—Cold Eurasia (WACE) pattern has been a notable feature in recent winters of the Northern Hemisphere. However, divergent results between model and observational studies of the WACE still remain. This study evaluates the performance of 39 climate models participating in the Coupled Model Intercomparison Project Phase 6 (CMIP6) in simulating the WACE pattern in winter of 1980–2014 and explores the key factors causing the differences in the simulation capability among the models. The results show that the multimodel ensemble (MME) can better simulate the spatial distribution of the WACE pattern than most single models. Models that can/cannot simulate both the climatology and the standard deviation of the Eurasian winter surface air temperature well, especially the latter, usually can/cannot simulate the WACE pattern well. This mainly results from the different abilities of the models to simulate the range and intensity of the warm anomaly in the Barents Sea—Kara seas (BKS) region. Further analysis shows that a good performance of the models in the BKS area is usually related to their ability to simulate location and persistence of Ural blocking (UB), which can transport heat to the BKS region, causing the warm Arctic, and strengthen the westerly trough downstream, cooling central Eurasia. Therefore, simulation of UB is key and significantly affects the model’s performance in simulating the WACE.

摘要

暖北极-冷欧亚(WACE)模态的显著增强是近年来北半球冬季气温变化的主要特征。然而,对于WACE的研究,模式与观测的结果仍然存在差异。本文评估了1980-2014年39个CMIP6模式对WACE模态的模拟能力,并讨论了导致模式模拟能力产生差异的关键因素。结果表明,相较于单个模式,多模式集合平均能更好地模拟WACE的空间分布特征。另外,当模式能够/不能很好地模拟欧亚冬季气温的气候态场和标准差场时,通常也能够/不能很好地模拟WACE,其中,对标准差场的模拟能力与对WACE的模拟效果联系更为紧密。这主要是由于模式对巴伦支海-喀拉海(BKS)地区暖异常的范围和强度的模拟能力不同所致。进一步分析表明,在BKS地区模拟的良好表现通常与模式能够较好地模拟乌拉尔阻塞高压(UB)的位置和持续性有关。因为UB引起的偏南风能够将热量输送到BKS地区,造成北极变暖,并加强下游的西风槽,使欧亚大陆中纬度地区降温。因此,对UB的模拟是影响模式模拟WACE的关键。