A modelling study of eddy-splitting by an island/seamount

Abstract

Abstract.A mesoscale eddy's trajectory and its interaction with topography under the planetary β and nonlinear effects in the South China Sea are examined using the MIT General Circulation Model (MITgcm). Warm eddies propagate to the southwest while cold eddies propagate to the northwest. The propagation speed of both warm and cold eddies is about 2.4 km day −1 in the model. The eddy trajectory and its structure are affected by an island or a seamount, in particular, under certain conditions, the eddy may split during the interaction with an island/seamount. We focus this research on two parameters R and S (where R and S are two dimensionless parameters of the island size and submergence depth; R is the ratio of the island radius to the eddy radius, and S is the ratio of the seamount submergence depth to the eddy vertical length). The results of sensitivity experiments with varying island or seamount geometry indicate that the eddy would split in the qualitative range of 1/4 < R < 2 and S < 1/5. The scale of the secondary eddy split-off decreases as the island diameter or the seamount submergence depth increases. In the splitting process, besides the off-spring eddy, there are also some filaments or eddies with opposite vorticity appearing around the eddy. Eddy-splitting, therefore, is an important way to transform energy from the mesoscale to sub-mesoscale in the ocean.

Could the two anticyclonic eddies during winter 2003/2004 be reproduced and predicted in the northern South China Sea?

“…However, most eddies may have interactions with topography, strong currents (western boundary current), and other eddies during their lifetime. The motion of an eddy will be modified and even split when approaching an island (Yang et al, 2017). It is also recognized that the western boundary is where eddies disappear (Zhai et al, 2010).…”

“…Many studies have tried to investigate mesoscale eddies in the NSCS (Wang et al, , 2008Jia et al, 2005). Based on the potential vorticity conservation equation and in situ survey data, Yuan and Wang (1986) pointed out that the bottom topography forcing might be the primary factor for the formation of anticyclonic eddies northeast of Dongsha Islands (DIs). Using survey CTD data in September 1994, Li et al (1998) recorded evidence of anticyclonic eddies in the NSCS and suggested these anticyclonic eddies are probably shed from the KC.…”

Clustering Complex Trajectories Based on Topologic Similarity and Spatial Proximity: A Case Study of the Mesoscale Ocean Eddies in the South China Sea

“…The method was applied to examine the complex trajectories of the 1993-2016 mesoscale ocean eddies in the South China Sea (SCS). It has been well documented that ocean eddies in the SCS split and merge frequently [13,23,24], producing many complex trajectories that are perfect for evaluation of our new method. Eddy splitting events usually lead to current deformation, material dispersion, and subsequent energy decay, which all affect water temperature and salinity, and, consequently, the marine ecosystems [23].…”

“…It has been well documented that ocean eddies in the SCS split and merge frequently [13,23,24], producing many complex trajectories that are perfect for evaluation of our new method. Eddy splitting events usually lead to current deformation, material dispersion, and subsequent energy decay, which all affect water temperature and salinity, and, consequently, the marine ecosystems [23]. By contrast, eddy merging events enhance seawater interaction in different regions and thus affect the trans-scale transmission of energy and entropy in turbulence [24].…”

“…To a certain extent, the previous studies have revealed the spatiotemporal characteristics and patterns, overall migration trend and channels of the SCS ocean eddies. However, very few, if any, previous studies ever tried to study complex ocean eddy trajectories generated by eddy splitting and merging activities in the SCS separately, though it has been well documented that splitting and merging are very important in studying ocean water interaction, material and energy transfer [23,24]. In this study, we applied our new proposed method to examine the complex eddy trajectories in the SCS with an aim to better reveal how the simple and complex eddy trajectories are different in the SCS.…”