Seasonal variation of the surface North Equatorial Countercurrent (NECC) in the western Pacific Ocean

The North Equatorial Countercurrent(NECC) is an important zonal fl ow in the upper circulation of the tropical Pacifi c Ocean, which plays a vital role in the heat budget of the western Pacifi c warm pool. Using satellite-derived data of ocean surface currents and sea surface heights(SSHs) from 1992 to 2011, the seasonal variation of the surface NECC in the western tropical Pacifi c Ocean was investigated. It was found that the intensity(INT) and axis position(Y_(CM)) of the surface NECC exhibit strikingly different seasonal fl uctuations in the upstream(128°–136°E) and downstream(145°–160°E) regions. Of the two regions, the seasonal cycle of the upstream NECC shows the greater interannual variability. Its INT and Y CM are greatly infl uenced by variations of the Mindanao Eddy, Mindanao Dome(MD), and equatorial Rossby waves to its south. Both INT and YC M also show semiannual signals induced by the combined effects of equatorial Rossby waves from the Central Pacifi c and local wind forcing in the western Pacifi c Ocean. In the downstream region, the variability of the NECC is affected by SSH anomalies in the MD and the central equatorial Pacifi c Ocean. Those in the MD region are especially important in modulating the Y CM of the downstream NECC. In addition to the SSH-related geostrophic fl ow, zonal Ekman fl ow driven by meridional wind stress also plays a role, having considerable impact on INT variability of the surface NECC. The contrasting features of the variability of the NECC in the upstream and downstream regions refl ect the high complexity of regional ocean dynamics.

Comparison of Some Features of the Subtropical Countercurrent, the North Equatorial Current and the North Equatorial Countercurrent in the Northwest Pacific Ocean

Based on the data of temperature and salinity of the 137°E section in the winters and summers from 1967 to 1995, the geo-strophic current of the section is calculated and analyzed, and the drifting tracks of the satellite tracking drift buoy distributed on the 144°E section are also analyzed. In light of the surface dynamic height distribution in the CSK atlas, this paper compares some features of the Subtropical Countercurrent, the North Equatorial Current and the North Equatorial Countercurrent. The main results are as follows:1. The Subtropical Countercurrent, the North Equatorial Current and the North Equatorial Countercurrent are not simple single currents, but have two branches or more. One of the common features of the three currents mentioned above is "multi-branching" of the current.2. The zonal distribution of the flow velocity structure, the alternate and intermittent occurrence of the eastward and westward flows, with a shallower flow layer and belonging to the surface flow or subsurface

西北太平洋副热带逆流、北赤道流、北赤道逆流几个特征的比较

根据 1 37°E断面 1 967～ 1 995年冬、夏季的温、盐资料 ,计算和分析该断面的地转流 ;分析 1 44°E断面上投放卫星跟踪漂流浮标的漂移轨迹 ;结合 CSK图集中的海面重力势分布 ,对副热带逆流、北赤道流和北赤道逆流几个特征的相同点和不同点进行比较 ,得出若干有益的结论 :( 1 )副热带逆流、北赤道流、北赤道逆流 ,并不是单纯的单支海流 ,而是存在着两支或多支现象 ;( 2 )流速结构的带状分布 ,东、西向流相互交错间隔出现 ,流层较浅 ,均为表层流或近表层流 ;( 3)多年平均而言 ,3支海流的流速以北赤道逆流最强 ,北赤道流次之 ,副热带逆流最弱 ;流量则不同 ,北赤道流最大 ,副热带逆流最小 ,北赤道逆流居中。 3支海流的流速夏季均大于冬季 ,但流量稍有差异 :副热带逆流和北赤道流均具有夏强、冬弱的特点 ,而北赤道逆流为冬强、夏弱 ;( 4 )冬季 ,副热带逆流的“源地”,位于巴士海峡和台湾以东“副热带脊”的一个“暖脊”中心附近海域 ;( 5)冬季 ,卫星跟踪漂流浮标的漂移轨迹 ,基本上反映出北赤道流和北赤道逆流的路径。但因副热带逆流区为涡旋频繁区 ,致使浮标漂移轨迹难以反映出副热带逆流的路径。

1993年冬季所罗门群岛─关岛断面地转流的初步分析

根据1993年1─2月“实验3”号考察船在霍尼亚拉港（瓜达尔卡纳尔岛）至关岛的断面观测的温、盐度资料，分析了该断面上的地转流结构，计算了南赤道流及北赤道逆流的地转流流速和流量。结果表明：在纬线方向上E向流与W向流呈带状分布，在垂向上也多为E向流与W向流交替出现。在南赤道流和北赤道逆流中都夹有与主流向相反的流动，它们的流量分别约占主流向流量的1／3和1／5。文章还将分析计算结果与手头掌握的文献报道的结果作了比较。

基于Argo浮标的西北太平洋环流特征分析

基于2004年1月-2009年12月月平均Argo（Array for Real-time Geostrophic Oceanography）温盐格点资料，结合 P-vector 方法重构了西北太平洋绝对地转流，重点分析了西北太平洋环流时空变化特征。结果表明，基于Argo资料西北太平洋三维结构特征与以前的研究结果是一致的。与WOA09（World Ocean Atlas 2009）计算的纬向流相比， Argo资料计算的纬向流要偏大。北赤道逆流（NECC）、北赤道流（NEC）、黑潮再生流（KCC）和黑潮延伸体（KE）都有明显的季节和年际变化。NECC 和 NEC 基本上呈现春强秋弱的季节变化特征， KCC和KE的季节特征与NECC和NEC存在反相关系。NECC和NEC表现出周期为1-2 a的年际信号， KCC和KE为非周期性的年际信号。表层NEC流核所在位置以及NEC南边界位置都有南移的趋势。另外， NEC、KCC和KE的流量也呈逐渐增大的趋势。

太平洋北赤道逆流年际变化的特征及其影响因子分析

采用SODA数据资料,分析了1950—2008年太平洋北赤道逆流(NECC)的年际变化特征及其与ENSO循环的联系。研究结果表明:(1)El Nio(La Nia)盛期是NECC流量由年际异常增大(减小)到异常减小(增大)的转折点;(2)NECC流轴的纬度在El Nio(La Nia)盛期达到年际异常最南(北)端;(3)NECC流轴在深度上呈西深东浅倾斜,El Nio(La Nia)盛期倾斜最弱(强)。通过构造典型ENSO循环的海表面风应力场,驱动一层半线性约化重力数值模式,结果验证了在NECC的年际变化中海表面风应力场是关键因素,而大洋波动(Kelvin波和Rossby波)和洋流本身是海洋内部的主要动力调整机制。

热带西太平洋北赤道逆流区涡旋统计分析

随着海洋技术的发展,中尺度的海洋过程越来越多的被揭示,中尺度涡旋作为重要的中尺度海洋过程,已经被大量的研究。但对于热带西北太平洋海区,中尺度涡旋特征的空间分布、季节变化以及移动规律等方面的研究还有所欠缺。本文使用Chelton提供的涡旋数据集,统计分析了热带西北太平洋海区涡旋特征的空间分布,发现以往研究较少的北赤道逆流(North Equatorial Countercurrent,NECC)区(A海区,120°~180°E,4°~6°N)较临近海域生成涡旋数量更多,涡旋半径、振幅、生命周期及非线性强度更大,移动距离更远,并且A海区涡旋经向移动距离服从伽马分布。涡旋在靠近西边界的区域更易向南移动,而在西边界以东的区域更易向北移动。A海区涡旋的生成数量具有明显的季节变化,主要受到流场剪切强度的影响。同时ENSO会对该区涡旋生成产生影响,其影响机制需要进一步的研究。

LICOM3.0海洋模式中太平洋北赤道逆流的模拟偏差分析

本文用CORE-IAF(Coordinated Ocean-ice Reference Experiments–Interannual Forcing)外强迫场分别强迫LICOM3(LASG/IAP Climate System Ocean Model Version 3)和POP2(Parallel Ocean Program version 2)两个海洋模式,并分析了这两个模式中太平洋北赤道逆流(NECC)的模拟结果。我们发现LICOM3和POP2模拟的NECC强度均弱于实测,这和Sun et al.(2019)的研究结果一致,也进一步证明了海洋模式中NECC偏弱是CORE-IAF外强迫场造成的,海表风应力及对应的风应力旋度是海洋模式准确模拟NECC的最主要因子。同时,我们也分析了NECC的模拟在动力机制上的差别,这里的动力强迫项包括风应力项、平流项和余项。我们发现模式的外强迫场虽然相同,但是两个模式中各动力强迫项(风应力项、平流项和余项)对NECC模拟的影响并不完全相同。

Variabilities of Surface Current in the Tropical Pacific Ocean

The Simple Ocean Data Assimilation (SODA) package is used to better understand the variabilities of surface current transport in the Tropical Pacific Ocean from 1950 to 1999. Seasonal variation, interannual and decadal variability analyses are conducted on the three major surface currents of the Tropical Pacific Ocean: the North Equatorial Current (NEC), the North Equatorial Countercurrent (NECC), and the South Equatorial Current (SEC). The transport of SEC is quite larger than those of NEC and NECC. The SEC has two maximums in February and August. The NEC has a small annual variation. The NECC has a maximum in October and is very weak in March and April. All currents have remarkable interannual and decadal variabilities. The variabilities of the NEC and the SEC relate to the winds over them well, but the relationship between the NECC and the wind over it is not close. Analysis related to El Nio-Southern Oscillation (ENSO) suggests that before El Nio (La Nia) the SEC is weaker (stronger) and the NECC is stronger (weaker), after El Nio (La Nia) the SEC is stronger (weaker) and the SEC is weaker (stronger). There is no notable relationship between the NEC and ENSO.

NUMERICAL SIMULATION OF THE MINDANAO EDDY AND TROPICAL CURRENTS OF PACIFIC OCEAN

Results of numerical simulation of currents in the western North Tropical Pacific Ocean by using a barotropic primitive equation model with fine horizontal resolution agreed well with observations and showed that the Mindanao Cyclonic Eddy located north of the equator and east of Mindanao Island exists during most of the year with monthly (and large seasonal) variations in scope . strength and central location . In June , an anticyclonic eddy occurs northeast of Halmahera Island, strengthens to maximum in August , exists until October and then disappears . The observed large-scale circulation systems such as the North Equatorial Current . the Mindanao Current and the North Equatorial Countercurrent are all very well reproduced in the simulations.