Investigating the causes of increased 20th-century fall precipitation over the southeastern United States.
Investigating the causes of increased 20th-century fall precipitation over the southeastern United States.
复制标题
调查 20 世纪美国东南部秋季降水量增加的原因。
作者：
D. Bishop;D. Bishop;A. P. Williams;R. Seager;Arlene M. Fiore;Arlene M. Fiore;Benjamin I. Cook;Benjamin I. Cook;J. Mankin;J. Mankin;J. Mankin;Deepti Singh;Deepti Singh;J. Smerdon;M. Rao;M. Rao
美国东部的大部分地区在20世纪经历了降水量的增加。确定这些趋势及其原因对于评估未来的水文气候风险至关重要。本文分析了美国1895年至2016年的降水趋势，发现墨西哥湾以北东南部地区的秋季降水量增加了近40%，主要是在20世纪中期以后增加的。由于秋季是东南-海湾的气候旱季，其他季节的降水变化不大，因此季节降水周期显著减少。东南-墨西哥湾秋季降水增加的原因是来自墨西哥湾的偏南水汽输送增加，这几乎完全是由与北大西洋副热带高压(NASH)以西加强的反气旋环流有关的更强风驱动的，而不是由于比湿度的增加。由观测到的SST强迫的大气模式和由历史人为强迫强迫的全耦合模式不能有力地模拟20世纪东南海湾的秋季湿润。SST强迫大气模式确实模拟了纳什周围增强的反气旋低层环流，但模拟的增强发生在比观测到的更西边的地方。CMIP5分析表明，考虑到历史和未来的温室气体强迫，东南-墨西哥湾秋季降水趋势为正的可能性增加。然而，单独的模式模拟(包括SST强迫模式和完全耦合模式)很少产生观测到的东南海湾秋季降水趋势。需要进一步研究秋季纳什西脊的模式表示，这将有助于我们更好地预测20世纪东南海湾秋季降水的增加是否会持续到未来。
Much of the eastern United States (US) experienced increased precipitation over the 20th century. Characterizing these trends and their causes is critical for assessing future hydroclimate risks. Here, US precipitation trends are analyzed during 1895-2016, revealing that fall precipitation in the southeastern region north of the Gulf of Mexico (SE-Gulf) increased by nearly 40%, primarily increasing after the mid-1900s. As fall is the climatological dry season in the SE-Gulf and precipitation in other seasons changed insignificantly, the seasonal precipitation cycle diminished substantially. The increase in SE-Gulf fall precipitation was caused by increased southerly moisture transport from the Gulf of Mexico, which was almost entirely driven by stronger winds associated with enhanced anticyclonic circulation west of the North Atlantic Subtropical High (NASH) and not by increases in specific humidity. Atmospheric models forced by observed SSTs and fully-coupled models forced by historical anthropogenic forcing do not robustly simulate 20th-century fall wetting in the SE-Gulf. SST-forced atmospheric models do simulate an intensified anticyclonic low-level circulation around the NASH, but the modeled intensification occurred farther west than observed. CMIP5 analyses suggest an increased likelihood of positive SE-Gulf fall precipitation trends given historical and future GHG forcing. Nevertheless, individual model simulations (both SST-forced and fully-coupled) only very rarely produce the observed magnitude of the SE-Gulf fall precipitation trend. Further research into model representation of the western ridge of the fall NASH is needed, which will help us better predict whether 20th-century increases in SE-Gulf fall precipitation will persist into the future.