Dominant Role of Subtropical Pacific Warming in Extreme Eastern Pacific Hurricane Seasons: 2015 and the Future Journal of Climate

The 2015 hurricane season in the eastern and central Pacific Ocean (EPO and CPO), particularly around Hawaii, was extremely active, including a record number of tropical cyclones (TCs) and the first instance of three simultaneous category-4 hurricanes in the EPO and CPO. A strong El Niño developed during the 2015 boreal summer season and was attributed by some to be the cause of the extreme number of TCs. However, according to a suite of targeted high-resolution model experiments, the extreme 2015 EPO and CPO hurricane season was not primarily induced by the 2015 El Niño tropical Pacific warming, but by warming in the subtropical Pacific Ocean. This warming is not typical of El Niño, but rather of the Pacific meridional mode (PMM) superimposed on long-term anthropogenic warming. Although the likelihood of such an extreme year depends on the phase of natural variability, the coupled GCM projects an increase in the frequency of such extremely active TC years over the next few decades for EPO, CPO, and Hawaii as a result of enhanced subtropical Pacific warming from anthropogenic greenhouse gas forcing. Grant no. NA14OAR4830101

2015年东太平洋与中太平洋（EPO、CPO）飓风季活动异常活跃，尤以夏威夷周边海域为甚，当年热带气旋（tropical cyclones, TCs）数量创下纪录，同时东太平洋与中太平洋海域首次观测到同时存在3场四级飓风的现象。2015年北半球夏季发育出强厄尔尼诺现象，部分学者将当年异常激增的热带气旋数量归因于该厄尔尼诺事件。然而，通过一系列针对性高分辨率模式试验可知，2015年东、中太平洋极端活跃的飓风季，主要诱因并非2015年厄尔尼诺引发的热带太平洋增暖，而是亚热带太平洋的增温过程。此类增温并非厄尔尼诺的典型特征，而是叠加在长期人为变暖之上的太平洋经向模（Pacific meridional mode, PMM）信号。尽管此类极端年份的发生概率取决于自然变率的相位，但耦合全球气候模式（coupled GCM）预测，未来数十年内，受人为温室气体强迫导致的亚热带太平洋增暖加剧影响，东太平洋、中太平洋及夏威夷周边海域出现极端活跃热带气旋年份的发生频率将有所提升。资助编号：NA14OAR4830101