We use altimeter-derived geostrophic velocities, with and without the addition of surface Ekman transports, to create trajectories for virtual parcels in the California Current System (CCS). The goal is to investigate the poleward transport of passive water parcels in the surface 50–100 m of the nominally equatorward system. Motivation for the study is provided by observations of anomalous biomass of copepods with warm water affinities along the Newport Hydrographic Line off central Oregon (44.7°N) during El Niño years, as well as during and following the 2014–2016 marine heat wave. By backward tracking virtual parcels from 44.7°N, we find that the most distant source of passive water parcels in the upper ocean during a one-year period of travel is from within the Southern California Bight (SCB), north of 30°N. To make that journey, parcels use the Inshore Countercurrent off southern and central California during summer–winter and the Davidson Current off northern California and Oregon during autumn–winter. The inclusion of small-scale eddy diffusion usually increases the number of parcels that reach more northern latitudes, while the inclusion of Ekman velocities more often reduces those numbers. Even so, parcels can travel from the SCB to central Oregon in either the Ekman layer or beneath it in the geostrophic flow. Using backward tracking, we find that parcels arrive at 44.7°N most often in winter–spring, least often in autumn. They arrive from within the large-cape region off northern California (41°–42°N) during all years and all months, from just south of the large-cape region (38°–39°N) during most years but seldom in autumn, from south of Monterey Bay along central California (36°N) and within the SCB (34.5°N) during a third (or less) of the years and only in winter-spring. The shortest average transit times are found in winter: for parcels reaching 44.7°N in February, the average transit time is 2 months for parcels coming from 41°–42°N, 4 months for parcels coming from 38°–39°N, and 5–6 months or more for parcels coming from south of 36°N. Transit times increase as the arrival time progresses from winter to autumn. The longest average transit times are for parcels reaching central Oregon in autumn (9–12 months in October for parcels coming from south of 39°N). This makes the journey a multi-generational task for the copepods. Interannual variability in the observed southern copepod species biomass off central Oregon correlates highly with years when more virtual parcels from the south reach central and northern Oregon, providing increased confidence in the results found with the altimeter-derived parcel trajectories.

中文翻译：

---

加利福尼亚洋流系统中高度计衍生的极向拉格朗日路径：第 1 部分


我们使用高度计衍生的地转速度，无论是否添加表面 Ekman 传输，在加利福尼亚洋流系统 （CCS） 中为虚拟包裹创建轨迹。目标是研究被动水地块在名义上向赤道系统 50-100 m 表面的极地传输。在厄尔尼诺年份以及 2014-2016 年海洋热浪期间和之后，对俄勒冈州中部 （44.7°N） 附近的纽波特水文线沿线具有温水亲和力的桡足类动物的异常生物量的观察提供了这项研究的动机。通过向后追踪北纬 44.7°的虚拟宗地，我们发现在一年的旅行期间，上层海洋中被动水宗地的最远来源来自北纬 30°以北的南加利福尼亚湾 （SCB） 内。 为了完成这段旅程，包裹在夏季至冬季使用加利福尼亚南部和中部附近的近海逆流，在秋冬季使用加利福尼亚北部和俄勒冈州附近的戴维森洋流。包含小尺度涡流扩散通常会增加到达更多北纬度的包裹数量，而包含 Ekman 速度通常会减少这些数量。即便如此，宗地可以在 Ekman 层或其下方的地转流中从 SCB 移动到俄勒冈州中部。使用反向跟踪，我们发现包裹在冬季至春季到达 44.7°N 的频率最高，秋季最少。它们在所有年份和所有月份都来自加利福尼亚北部（北纬 41°-42°）附近的大开普地区，在大多数年份从大开普地区（北纬 38°-39°）以南到达，但在秋季很少，从加利福尼亚中部（北纬 36°）的蒙特利湾南部（北纬 36°）和 SCB （34.5°N），在三分之一（或更少）的年份中，仅在冬春季。冬季的平均运输时间最短：对于 2 月份到达北纬 44.7°的包裹，来自北纬 41°-42°的包裹的平均运输时间为 2 个月，来自北纬 38°-39°的包裹为 4 个月，来自北纬 36°以南的包裹的平均运输时间为 5-6 个月或更长时间。 运输时间会随着到达时间从冬季到秋季的增加而增加。最长的平均运输时间是在秋季到达俄勒冈州中部的包裹（来自北纬 39°以南的包裹在 10 月为 9-12 个月）。这使得这段旅程成为桡足类动物的多代任务。在俄勒冈州中部附近观察到的南方桡足类物种生物量的年际变化与来自南部的更多虚拟宗地到达俄勒冈州中部和北部的年份高度相关，从而增加了对高度计衍生宗地轨迹发现的结果的信心。