Eddy characteristics in the northern South China Sea as inferred from Lagrangian drifter data

Abstract

Abstract. Cyclonic and anticyclonic eddies from large scale to submesoscale in the northern South China Sea (NSCS) have been statistically characterized based on the satellitetracked Lagrangian drifters using our developed geometric eddy identification method. There are in total 2208 eddies identified, 70 % of which are anticyclonic eddies. If the submesoscale eddies are eliminated, the other eddies in the NSCS will show a 1.2:1 ratio of the number of anticyclones (210) to the number of cyclones (171). The spatial distribution of the eddies is regional: in southwest of Taiwan, the number of anticyclones dominates the number of cyclones, and most of them are the submesoscale anticyclones with small radii; in contrast, the large and medium cyclonic eddies are a little more than the same scale anticyclonic eddies in northwest of Luzon. The temporal distribution of eddy number in the NSCS has a close relation with the Asian monsoon. The number of the large and medium eddies peaks during the winter monsoon, while the submesoscale eddies are apt to generate in the summer monsoon. The spatial and temporal patterns have a good agreement with the results of the sea surface height anomaly (SSHA). The maximum and mean tangential velocities of anticyclones (cyclones) are 40 (30) cm s −1 and 25 (15) cm s −1 , respectively. The calculated normalized vorticities from drifters suggest that although the mesoscale eddies may be considered in geostrophic balance, ageostrophic dynamics and centrifugal effects may play an important role for the growth and decay of the mesoscale cores.

Eddy characteristics in the South Indian Ocean as inferred from surface drifters

“…Due to the long distance between satellite tracks, altimetry can hardly detect eddies with radius r < 40 km (e.g., Chelton et al, 2011). Whereas surface drifters can detect submesoscale eddies with radius r < 10 km (Berti et al, 2011;Li et al, 2011;Schroeder et al, 2012). Surface drifters have a 6 h temporal resolution, much more than altimetry data which, so far, usually have 7-or 1-day intervals available to the public.…”

“…Surface drifters have a 6 h temporal resolution, much more than altimetry data which, so far, usually have 7-or 1-day intervals available to the public. Surface drifters give reliable in situ observations and have been extensively used in other ocean regimes (Deverdiere, 1983;Chaigneau and Pizarro, 2005;Hamilton, 2007;Li et al, 2011;Zu et al, 2012).…”

A clustering analysis of eddies' spatial distribution in the South China Sea

“…Much work tries to investigate their dynamic characteristics and formation mechanisms, especially using statistical approaches (Wang et al, 2003;Wu and Chiang, 2007;Xiu et al, 2010;Li et al, 2011). Spatial variation is important for statistical analysis because patterns or rules in different regions are generally distinguished from each other.…”

“…Spatial variation is important for statistical analysis because patterns or rules in different regions are generally distinguished from each other. While some researchers focus their studies on particular regions of SCS (Fang et al, 2002;Wu and Chiang, 2007;Yuan et al, 2007;Li et al, 2003;Yang et al, 2000;Yuan and Li, 2008), some others study the whole maritime area of SCS by geographical divisions (Li et al, 2011;Wang et al, 2003;Lin et al, 2007;Chen et al, 2011). Wang et al (2003) first proposed a four-zone division for the SCS according to limited knowledge of eddy generation mechanisms, and used it to group eddies for analysis.…”

“…al. (2011) and Li et al (2011) also discussed their statistical findings of different geographic zones. However, few studies have explored the spatial characteristics embedded in eddies' generation data or discussed the spatial pattern reflected by their locations.…”