主流系与西太平洋暖池变异机制研究进展

RESEARCH PROGRESSES IN THE VARIABILITY OF WESTERN PACIFIC MAIN CURRENT SYSTEM AND WARM POOL

中国科学院战略性先导科技专项重点任务2以热带西太平洋主流系和暖池为主要研究对象,基于西太平洋和印尼海科学观测网综合观测数据,结合动力理论分析和数值模拟结果,在主流系和西太暖池的三维结构、变异规律和动力机制,以及西太与周围海域之间物质能量交换等方面取得了原创性成果。在上层主流系和暖池变异方面,首次直接观测到棉兰老潜流(MUC)、吕宋潜流(LUC)和北赤道潜流(NEUC)等次表层潜流及其多尺度变异,给出了三支潜流相互间的水源关系,揭示了潜流系统强劲的季节内变化特征及其与中尺度涡旋活动的关系,并进一步分析了棉兰老流(MC)/MUC年际变异及其控制因素。西太平洋主流系平流输送在暖池形成中起到了主要作用,而且暖池北部区域自20世纪90年代起出现显著的扩张现象,是由混合层厚度变浅导致。在中深层环流特征和机制方面,发现南北半球中层水团的交换通道、机制和显著交换周期;丰富了对赤道西太平洋中层流结构特征和变异的认识,同时突破了对西太平洋深层环流结构特征和变异规律的认知局限,例如中深层流流速自北向赤道增加,其变化远大于平均值,菲律宾海盆中部深层流以西南-东北方向为主,赤道区域中深层流以纬向东西交替的射流为主等。在西太与周围海域之间物质能量交换方面,通过在印尼贯穿流(ITF)源区及印尼海的同步走航及定点潜标观测,揭示了MC在苏拉威西海和马鲁古海峡交汇处的流径跃变在2015—2016超强El Ni?o的发生起重要作用,西边界流区的非线性反射对ENSO事件的发生发展起至关重要的作用。上述原创性成果显著提升了热带西太平洋环流动力学的认知水平。

One of the key task of the Strategic Priority Research Program of the Chinese Academy of Sciences entitled ＂Western Pacific Ocean System＂（WPOS） aims at the comprehensive research into main current system and warm pool in the western Pacific. By analyzing the deep-sea observation data, WPOS has achieved significant progresses on the structure, variability, and dynamical mechanism of three-dimensional circulations in the Western Pacific, and the mass and energy exchanges between the Western Pacific Ocean and its surrounding areas. First, on the upper ocean circulations and the warm pool, we directly observed and hence confirmed the existence of subsurface undercurrents（the Mindanao Undercurrent, Luzon Undercurrent, and North Equatorial Undercurrent） east of the Philippines, clarified the relationship among the three undercurrents, and revealed the significant intraseasonal variability of them and their relationships with mesoscale eddies, and analyzed the interannual variability of MC/MUC（Mindanao Current/Mindanao Undercurrent） and its driving force. The heat advection by ocean circulations in the western pacific play important roles in the formation and maintenance of the warm pool, and the northern part of the warm pool has significantly expanded since 1990 s, which is related to the reduction of the mixed layer. Second, on the intermediate and deep ocean circulations, we explored the alternating period of intermediate waters exchange from the Northern and Southern Hemispheres, achieved a more complete understanding of the intermediate current system, and made a breakthrough in understanding the characteristic and variability of deep ocean currents. The intermediate and deep ocean velocities increase equatorward with standard deviation much larger than mean. The intermediate and deep ocean currents flowed mainly in the meridional direction in the central Philippine Basin, and were dominated by a series of alternating westward and eastward zonal jets in the Caroline Basin. I Third, on mass and energy exchanges between the western Pacific and its surrounding areas, we conducted successfully three joint cruises in the Indonesian seas and the ITF（Indonesia Throughflow） entrance area. The observations suggest that the leap transition of the MC pathway between the Sulawesi Sea and the Maluku Strait play a key role in the 2015/16 supper El Ni？o event. The nonlinearity of the western boundary current reflections is very important in the developing of ENSO.