Wise Erika K, Dannenberg Matthew P
Department of Geography, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA.
Sci Adv. 2017 Jun 7;3(6):e1602263. doi: 10.1126/sciadv.1602263. eCollection 2017 Jun.
Moisture delivery to western North America is closely linked to variability in the westerly storm tracks of midlatitude cyclones, which are, in turn, modified by larger-scale features such as the El Niño-Southern Oscillation system. Instrumental and modeling data suggest that extratropical storm tracks may be intensifying and shifting poleward due to anthropogenic climate change, but it is difficult to separate recent trends from natural variability because of the large amount of decadal and longer variation in storm tracks and their limited instrumental record. We reconstruct cool-season, midlatitude Pacific storm-track position and intensity from 1693 to 1995 CE using existing tree-ring chronologies along with a network of newly developed chronologies from the U.S. Pacific Northwest, where small variations in storm-track position can have a major influence on hydroclimate patterns. Our results show high interannual-to-multidecadal variability in storm-track position and intensity over the past 303 years, with spectral signatures characteristic of tropical and northern Pacific influences. Comparison with reconstructions of precipitation and tropical sea surface temperature confirms the relationship between shifting drought patterns in the Pacific Northwest and storm-track variability through time and demonstrates the long-term influence of El Niño. These results allow us to place recent storm-track changes in the context of decadal and multidecadal fluctuations across the long-term record, showing that recent changes in storm-track intensity likely represent a warming-related increase amplified by natural decadal variability.
北美洲西部的水分输送与中纬度气旋的西风风暴路径变化密切相关，而西风风暴路径又会受到诸如厄尔尼诺-南方涛动系统等大尺度特征的影响而发生改变。仪器观测和模型数据表明，由于人为气候变化，温带风暴路径可能正在增强并向北移动，但由于风暴路径存在大量年代际及更长时间尺度的变化，且其仪器记录有限，因此很难将近期趋势与自然变率区分开来。我们利用现有的树木年轮年表以及美国太平洋西北地区新开发的年表网络，重建了公元1693年至1995年冷季的中纬度太平洋风暴路径位置和强度，在该地区，风暴路径位置的微小变化会对水文气候模式产生重大影响。我们的结果显示，在过去303年里，风暴路径位置和强度存在高年际到年代际变化，并具有热带和北太平洋影响的光谱特征。与降水和热带海表面温度重建结果的比较证实了太平洋西北地区干旱模式变化与风暴路径随时间变化之间存在关联，并证明了厄尔尼诺现象具有长期影响。这些结果使我们能够将近期风暴路径变化置于长期记录中的年代际和年代际波动背景下进行考量，表明近期风暴路径强度变化可能代表了由自然年代际变率放大了的与变暖相关的增加。
