Wu Chau-Ron, Lin Yong-Fu, Qiu Bo
Department of Earth Sciences, National Taiwan Normal University, Taipei, Taiwan.
Department of Oceanography, University of Hawaii at Manoa, Honolulu, Hawaii, USA.
Sci Rep. 2019 Feb 15;9(1):2162. doi: 10.1038/s41598-019-38479-w.
Variability in surface currents is mainly induced by the time-varying wind forcing. Recent studies have revealed robust pronounced changes in the atmospheric circulation over the Pacific came with the Pacific Decadal Oscillation (PDO). However, the PDO is a climate index based on sea surface temperature (SST) variations, and may not be appropriately considered as a climate forcing. Here, we suggest the Atlantic SST variability is the ultimate forcing leading to changes in the atmospheric circulation and surface winds over the North Pacific. Anomalous warm North Atlantic and cold South Atlantic leads to weak Hadley cell in the Northern Hemisphere, resulting in a northward displacement of the ITCZ as well as a positive wind stress curl anomaly in the Pacific subtropical region, which would reduce the North Pacific subtropical gyre (NPSG). Associated with reduced sea surface height in the subtropics by the weakened NPSG, the North Equatorial Current (NEC) is weakened based on geostrophy. Changes in basin-scale winds further result in the southward migration of the tropical gyre and consequential downstream ocean circulation.
表层海流的变化主要是由随时间变化的风应力引起的。最近的研究表明，随着太平洋年代际振荡（PDO）的出现，太平洋上空的大气环流发生了显著的变化。然而，PDO是一个基于海表温度（SST）变化的气候指数，可能不宜被视为一种气候强迫。在此，我们认为大西洋海温变化是导致北太平洋大气环流和表层风变化的最终强迫因素。北大西洋异常变暖而南大西洋异常变冷会导致北半球哈得莱环流减弱，从而使热带辐合带向北移动，并在太平洋亚热带地区出现正的风应力旋度异常，这将削弱北太平洋亚热带环流（NPSG）。由于NPSG减弱导致亚热带海表高度降低，根据地转平衡，赤道北流（NEC）也会减弱。流域尺度风的变化进一步导致热带环流南移以及随之而来的下游海洋环流变化。
