SLA-Based Orthogonal Parallel Detection of Global Rotationally Coherent Lagrangian Vortices

Abstract

In this paper, we present a highly effective orthogonal parallel algorithm for identifying global rotationally coherent Lagrangian vortices (RCLVs) in heterogeneous systems and a long-time-scale global SLA-based RCLVs product. First, a manycore parallel computing method is used to accelerate the Lagrangian-averaged vorticity deviation (LAVD) computing process. The computation is approximately 8000 times faster than that of a previous method. Second, the global LAVD field is divided into several regions. These regions are searched with a multiprocess CPU parallel pool to identify simultaneously RCLVs. All the identified RCLVs in these regions are merged seamlessly into a global eddy map. The algorithm improves the global RCLV identification efficiency, making the proposed method approximately 20 times faster than a single-threaded method. The LAVD manycore computing method and the RCLV multiprocess parallel method are orthogonally combined. The resulting algorithm is at least 500 times faster than previous nonparallel methods, making the computing of global RCLVs feasible. Third, the advection of Lagrangian particles in RCLVs and Eulerian eddies is analyzed to demonstrate the material coherence of RCLVs and the reliability of our algorithm. Finally, a global RCLVs product from 1993 to 2019 containing 52,567 eddies is produced with a 90-day time interval. This is the first time that a long-time-scale global Lagrangian eddy product has been presented.

A Lagrangian coherent eddy atlas for biogeochemical applications in the North Pacific Subtropical Gyre

“…To make such an assumption, Lagrangian coherence metrics can be used, but they are computationally expensive and rarely invoked for biophysical interpretations, with a few exceptions. He et al (2022) found chl a aggregations in coherent cyclonic eddies, and low chl a in coherent anticyclones of the Northwest Pacific. Hernández-Carrasco et al (2023) found that Lagrangian coherent eddies favor diatom growth in the oligotrophic Mediterranean Sea.…”

“…The latter two are thought to enhance "monopole" chl a anomalies, where elevated or depressed levels of chl a are located in the core of an eddy. Satellite observations have revealed chl a monopoles in eddies shed from the Gulf Stream and other western boundary currents (Waite et al, 2007;Gaube et al, 2013Gaube et al, , 2014He et al, 2022), the Agulhas rings (Lehahn et al, 2011;Villar et al, 2015), the North Pacific Ocean (Calil and Richards, 2010;Guo et al, 2017;He et al, 2022), the South Indian Ocean (Gaube et al, 2014), and the Southern Ocean (Dawson et al, 2018;Frenger et al, 2018). Disentangling the contributions of eddy trapping and pumping to chl a monopoles remains a challenge, in part because dynamical trapping is difficult to quantify.…”

“…Here we define Lagrangian eddies (or RCLVs) using the LAVD method owing to its objectivity, computational efficiency, and mathematical foundation describing material rotation. RCLVs are ubiquitous in satellite altimetry observations (Abernathey and Haller, 2018;Tian et al, 2022;Xia et al, 2022b;Liu and Abernathey, 2023), and their trapping properties have been validated with in situ trajectories of Argo floats (Liu and Abernathey, 2023) and drifters (Encinas-Bartos et al, 2022).…”

A global Lagrangian eddy dataset based on satellite altimetry

“…Although a small amount of filaments exists, the RCLV defined by CD < 0.1 can basically trap the initial water parcels and maintain the coherent structure over the lifetime. It is clear that, the thresholds of 0.25 and 0.01 (adopted by Tian et al, 2022) will greatly overestimate and underestimate, respectively, the size of the coherent eddy. This parameter combination has been employed successfully in our previous studies (Liu et al, 2019(Liu et al, , 2022a.…”

“…Based on numerical model outputs, Xia et al (2022) used the three-dimensional LAVD method to detect global coherent eddies, and they estimated the coherent transport across each latitude or longitude to be only about 1 Sv. Tian et al (2022) also applied the LAVD method to global eddy detection and presented a 90-day RCLVs dataset, but they adopted a very tight threshold to define the eddy boundary (Tarshish et al, 2018), which would greatly underestimate the size of Lagrangian eddies (see Figure 4). Nearly all public global eddy datasets are based on the Eulerian framework, and identifying coherent eddies is not an easy task.…”