A Modeling- and Process-Oriented Study to Investigate the Projected Change of ENSO-Forced Wintertime Teleconnectivity in a Warmer World
A Modeling- and Process-Oriented Study to Investigate the Projected Change of ENSO-Forced Wintertime Teleconnectivity in a Warmer World
复制标题
DOI：
10.1175/jcli-d-18-0803.1
复制
发表时间：
2019-12-01
影响因子：
4.9
通讯作者：
Cassou, Christophe
中科院分区：
文献类型：
--
作者：
Drouard, Marie;Cassou, Christophe
随着气候变暖，ENSO 和相关远程连通性的预期变化仍然存在相当大的不确定性。使用 CNRM-CM5 耦合模型的两个起搏器实验集合在完美的模型框架中设计，以对比工业化前时期与较温暖背景状态之间的 ENSO 强制遥连通性（从二十一世纪末 RCP8.5 恒定强迫下的长期稳定模拟获得）。对平均背景状态最显着的敏感度出现在北大西洋，那里的 ENSO-NAO 遥相关在较温暖的世界中显着增强。我们将这种变化归因于（i）北太平洋上空更强且向东延伸的平均高层急流，（ii）北太平洋上空的 ENSO 遥相关东移，以及（iii）北大西洋上空赤道移动和增强的平均急流。它们共同充当更有效的波导，使来自太平洋的天气风暴更好地渗透到大西洋。下游渗透到北大西洋盆地迫使 NAO 更系统地进行波浪破碎。遥相关的增强相对于 ENSO 相位是不对称的，并且主要对拉尼娜事件敏感。尽管太平洋急流在寒冷事件期间往往会向西收缩并向北移动，但与工业化前时期相比，平均变化是太平洋和大西洋急流在较温暖的气候下仍然保持连接，从而确保优先的反气旋波在北大西洋下游破裂，最终导致 NAO+ 事件。
Considerable uncertainties remain about the expected changes of ENSO and associated teleconnectivity as the climate is warming. Two ensembles of pacemaker experiments using the CNRM-CM5 coupled model are designed in a perfect model framework to contrast ENSO-forced teleconnectivity between the preindustrial period versus a warmer background state (obtained from a long stabilized simulation under late-twenty-first-century RCP8.5 constant forcing). The most notable sensitivity to the mean background state is found over the North Atlantic, where the ENSO-NAO teleconnection is considerably reinforced in a warmer world. We attribute this change to (i) a stronger and eastward-extended mean upper-level jet over the North Pacific, (ii) an eastward-shifted ENSO teleconnection over the North Pacific, and (iii) an equatorward-shifted and reinforced mean jet over the North Atlantic. These altogether act as a more efficient waveguide, leading to a better penetration of synoptic storms coming from the Pacific into the Atlantic. This downstream penetration into the North Atlantic basin forces more systematically the NAO through wave breaking. The reinforcement in the teleconnection is asymmetrical with respect to the ENSO phase and is mainly sensitive to La Nina events. Even though the Pacific jet tends to retract westward and move northward during cold events, mean changes are such that both Pacific and Atlantic jets remain connected in a warmer climate by contrast to the preindustrial period, thus ensuring preferred anticyclonic wave breaking downstream over the North Atlantic leading ultimately to NAO+ events.