| 摘要: |
| 北赤道逆流（NECC）作为热带太平洋环流系统的重要组成部分，深刻影响着热带太平洋的海气相互作用及全球气候变化。因此，深入理解NECC的结构及其变异，对于理解厄尔尼诺-南方涛动（ENSO）的演变、提高气候模式的模拟和预测能力具有重要意义。本文使用赤道西太平洋130°E断面获取的水文观测数据，结合卫星高度计数据和再分析数据，分析了2017/18弱拉尼娜事件和2018/19弱厄尔尼诺事件期间赤道西太平洋源区NECC的温盐流特征及变异机理。研究发现，在2017/18弱拉尼娜事件期间，源区NECC的年际变异与传统认知存在较大差异，表现为输运量显著增加且流轴向南偏移，其机制在于观测期间异常强劲且中心位置向西北偏移的哈马黑拉涡（HE）的影响。在2018/19弱厄尔尼诺事件期间，源区NECC输运进一步增强，达到40-45Sv，接近其月平均气候态输运的两倍，此现象与该海域温跃层深度的经向梯度增强及HE增强密切相关。水团分析表明，两次事件中NECC源区水团特征及分布也呈现异常显著的差异，表现为在2018/19弱厄尔尼诺事件期间，南太平洋热带水（SPTW）向北入侵异常强劲，入侵纬度达到6°N附近，且盐度极值可达到35.4PSU;而在2017/18弱拉尼娜事件中，SPTW北向入侵限制在5°N以南，且盐度降低至35.1PSU。上述水团的差异主要受两次事件中海洋环流的影响：由于2018/19观测期间新几内亚沿岸流/潜流和异常强劲的HE共同作用，导致SPTW的跨赤道输运异常强劲。本文的研究结果表明，西太NECC源区海洋环流和水团的年际变异在不同ENSO位相期间存在显著差异，局地涡旋的变异起着非常重要的调制作用；同时，弱ENSO事件期间该海域的变化与常规ENSO事件也存在较大差异。上述结果为深化ENSO多样性对西太平洋环流影响的认知及提升数值模式在该海域的模拟精度提供了宝贵的观测支撑和重要参考。 |
| 关键词: 北赤道逆流 ENSO 哈马黑拉涡 跨赤道输运 |
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| 基金项目:国家自然科学基金项目，42276012 号；“一带一路”国际科学组织联盟联合研究合作专项资助，ANSO-CR-KP-2022-08 号；崂山实验室科技创新项目，LSKJ202202502 号；中国科学院战略性优先发展研究计划，XDB42000000 号 |
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| HYDROLOGICAL CHARACTERISTICS AND MECHANISM OF THE NORTH EQUATORIAL COUNTERCURRENT SOURCE REGION OF THE PACIFIC OCEAN UNDER DIFFERENT ENSO STATES OBSERVED IN 2017-2018 |
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YuXiaotong1,2, ZhouHui1,2, LiuXuwqi1, YangWenlong3, LiuHengchang4,5, LiuJuan5
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1.Institute of Oceanology, Chinese Academy of Sciences;2.University of Chinese Academy of Sciences;3.Naval Research Institute;4.State Key Laboratory of Geo-Information Engineering;5.Beijing institute of Applied Meteorology
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| Abstract: |
| As an important component of the tropical Pacific circulation system, the North Equatorial Countercurrent (NECC) profoundly influences air-sea interactions in the tropical Pacific and the global climate change. Therefore, a thorough understanding of the NECC structure and its variation is of great significance for unerstanding the evolution of the El Ni?o -Southern Oscillation (ENSO), and improving the ability of climate model simulation and prediction. In this paper, the thermohaline flow characteristics and variation mechanism of NECC in the source region of the western Equatorial Pacific during the weak La Ni?a events of 2017/18 and the weak El Ni?o events of 2018/19 are analyzed using the hydrological observation data obtained from the 130°E section of the Western Equatorial Pacific Ocean, combined with satellite altimeter data and reanalysis data. It is found that during the 2017/18 weak La Ni?a event, the interannual variation of NECC in the source region is quite different from the traditional understanding, as the transport volume increases significantly and the flow axis shifts southward, which is caused by the influence of the Hamahera Eddy (HE), which is unusually strong and the center shifts to the northwest during the observation period. During the weak El Ni?o event 2018/19, NECC transport in the source region was further enhanced, reaching 40-45Sv, nearly twice the monthly mean climatic state transport, which is closely related to the enhancement of meridonal gradient in the depth of the thermocline and HE. The water mass analysis showed that the characteristics and distribution of the water mass in the NECC source area also presented unusually significant differences between the two events, as shown by the fact that during the weak El Ni?o event 2018/19, the South Pacific tropical water (SPTW) invaded northwestward very strongly, the invasion latitude reached around 6°N, and the extreme salinity reached 35.4PSU. During a weak La Ni?a event in 2017/18, SPTW northbound intrusion was limited to south of 5°N and salinity was reduced to 35.1PSU. The difference in the above water mass was mainly influenced by the ocean circulation during the two events: the combination of the New Guinea coastal current/undercurrent and the unusually strong HE during the 2018/19 observation resulted in the unusually strong trans-equatorial transport of SPTW. The results of this study show that the interannual variation of ocean circulation and water mass in the NECC source region of the West Pacific is significantly different during different ENSO phases, and the variation of local eddies plays a very important modulating role. At the same time, the changes of the sea area during weak ENSO events are different from those of conventional ENSO events. These results provide valuable observation support and important reference for deepening the understanding of the effect of ENSO diversity on the Western Pacific circulation and improving the simulation accuracy of numerical models in this area. |
| Key words: North Equatorial Countercurrent ENSO Hammarhera Eddy Trans-equatorial transport |