Comparative analysis of four types of mesoscale eddies in the north pacific subtropical countercurrent region – part I spatial characteristics

Abstract

The North Pacific Subtropical Countercurrent (STCC) region has high mesoscale eddy activities due to its complex circulation structure. This study divides these mesoscale eddies into four types: cyclonic cold-core eddy (CCE), anticyclonic warm-core eddy (AWE), cyclonic warm-core eddy (CWE), and anticyclonic cold-core eddy (ACE) according to the rotation direction of the eddy flow field and the sign of average temperature anomaly within the eddy after spatial high-pass filtering. CCE and ACE are called normal eddies, while CWE and ACE are named abnormal eddies. Using eddy-resolving model data (OFES), this work finds that the abnormal eddy phenomenon mainly occurs in the ocean’s upper layer. The eddy number proportion for CCEs, AWEs, CWEs, and ACEs at the sea surface is 35.60, 32.08, 12.95, and 19.37%. The corresponding average radius is 79.14 ± 3.7, 83.34 ± 3.75, 73.74 ± 4.14, and 79.46 ± 3.89 km, respectively. Each type of eddy’s average amplitude is about 3 cm. Regarding the eddy average eccentricity, the four types of eddies have very close eccentricities, with a range of 0.73 ~ 0.76. If the types of eddies are not distinguished, the eddies generated north of 21°N tend to move southward, while eddies generated south of that latitude tend to move northward. The depth of CCEs, AWEs, CWEs, and ACEs with average eddy nonlinearity larger than one is concentrated in the ocean’s upper layer at 109.0, 116.0, 159.0, and 52.0 m, respectively. This study deepens the understanding of the spatial distribution characteristics of mesoscale eddies in the STCC region.

Spatiotemporal Variation of Anticyclonic Eddies in the South China Sea during 1993–2019

“…It should be noted that there are still some abnormal eddies in the SCS that cannot be detected by our method. The eddies that have negatively correlated SSH-SST relationships [63,64] may also play an important role in ocean dynamics and biogeochemical activities. These eddies are also found in the SCS [35,36], though with low frequency.…”

Evolution of Different Types of Eddies Originating from Different Baroclinic Instability Types

“…The method identifies the eddies' centers from geostrophic current anomaly data obtained from satellite altimeters and then obtains the eddies' boundaries, which allows for an easier and more flexible way to identify eddies within the velocity field. Numerous studies have validated this method's effectiveness, and it has been extensively utilized in various regions [33][34][35][36][37][38][39][40][41]. We detected and tracked mesoscale eddies globally using the daily average data of sea level anomaly (SLA), preserving only those with lifetimes exceeding 30 days in the results.…”

Composite vertical structures and spatiotemporal characteristics of abnormal eddies in the Japan/East Sea: a synergistic investigation using satellite altimetry and Argo profiles

“…From a conventional perspective, AEs/CEs are often associated with a warmer/colder cores in comparison to that of the background water mass. Nevertheless, recent studies have identified numerous abnormal eddies with opposite-temperature structures, including AEs with cold cores and CEs with warm cores (Itoh and Yasuda, 2010;Liu et al, 2021;Ni et al, 2021;An et al, 2022;Qi et al, 2022;Sun et al, 2023). In this study, these eddies are respectively named cold-core anticyclonic eddies (CAEs) and warm-core cyclonic eddies (WCEs).…”

“…An abnormal anticyclonic eddy surface, characterized by a lensshaped structure and a cold core, was investigated by 3-day insitu observations in the northern South China Sea (SCS), the conductivity-temperature-depth(CTD) and acoustic doppler current profiler(ADCP) measurements produced comprehensive information about the eddy's characteristics (Qi et al, 2022). Using eddy-resolving model data (OFES) from 2008 to 2017, a considerable amount of abnormal eddies were found to exist in the Kuroshio-Oyashio extension region and North Pacific Subtropical Countercurrent (STCC) region, and their spatial and seasonal variations have been exhaustively investigated (An et al, 2022;Sun et al, 2023). Although their definitions and detection methods of abnormal eddies are different, it can be confirmed that abnormal mesoscale eddies are ubiquitous in the global ocean.…”