Spatiotemporal Variations of Mesoscale Eddies in the Sulu Sea

Abstract

Mesoscale eddies have been observed in the Sulu Sea, but their characteristics have not been well described. This study investigates the eddy population in the Sulu Sea using 22 years of satellite altimeter data with high spatiotemporal resolution. On average, there are approximately 1.6 eddies observed in the Sulu Sea each day and 1.8 eddy tracks generated each month. Two of the main eddy genesis regions are west of Negros Island and the Zamboanga Peninsula. The mean radius, lifespan and propagation speed of the eddies are 76.6 km, 32 days and 4.5 cm/s, respectively. The eddy radius and amplitude are generally large in the central Sulu Sea but small on its margin. The mean eddy kinetic energy and vorticity generally monotonically decrease from south to north, consistent with the distributions of background current kinetic energy. Over the seasonal cycle, there are more cyclonic eddies during boreal winter, and they tend to have a larger amplitude and radius than the other 3 seasons, while there are more anti‐cyclonic eddies during boreal summer, and they tend to have a larger amplitude and radius than the other 3 seasons. The instability of the mean current and the island gap wind jets are the two key eddy genesis mechanisms in the Sulu Sea.

Spatiotemporal Variations of Mesoscale Eddies in the Southeast Indian Ocean

“…Journal of Geophysical Research: Oceans (He et al, 2017), this indicates that the magnitude of relative vorticity is mainly dominated by the characteristic particle velocity; thus, also determined by the amplitude. Moreover, the decrease in eddy radii towards higher latitudes also contributes to increasing relative vorticity along the path of the LC (Morrow et al, 2004).…”

“…The distribution of relative vorticity of eddies exhibits a similar spatial pattern as that of EKE (Figure 2c,d). Since the characteristic relative vorticity ξ for an eddy is equal to U / L (He et al, 2017), this indicates that the magnitude of relative vorticity is mainly dominated by the characteristic particle velocity; thus, also determined by the amplitude. Moreover, the decrease in eddy radii towards higher latitudes also contributes to increasing relative vorticity along the path of the LC (Morrow et al, 2004).…”

“…The region where the most eddies are shed is west of Shark Bay, where topography changes rapidly and the flow direction turns abruptly from towards the southwest to towards the southeast (Fang & Morrow, 2003), with the eddy genesis of 41 eddies in the 112°E‐27°S 1° × 1° bin for the period 1993–2017 (Figure 1a), indicating the importance of islands and irregular coastlines in generating mesoscale eddies (Bracco & Pedlosky, 2003; Fang & Morrow, 2003). The eddy translation velocity vectors are calculated by a forward difference scheme for each day of eddy centroid displacement, following He et al (2017). We find that the eddy translation velocities are roughly aligned with the σ 0 contours in the range of 25 ~ 26.4 kgm −3 at 150 m in our region of concern, which is consistent with previous studies suggesting that eddies tend to propagate westward along the isopycnals, after leaving their formation areas (Figure 1b; Dilmahamod et al, 2018; Fang & Morrow, 2003; Morrow et al, 2004).…”

“…As the eddy size can be largely estimated from the Rossby radius, a nearshore band generally causes a shallower water depth, and thus a smaller Rossby radius and eddy size (Chelton et al, 1998). Moreover, energy dissipation due to increased friction in coastal areas provides an alternative explanation for the smaller eddy size near the coast (He et al, 2017). The EKE spatial pattern correlates well with that of the amplitude patterns (Figure 2a,c).…”

Revisit the Vertical Structure of the Eddies and Eddy‐Induced Transport in the Leeuwin Current System

“…The criteria 1 to 4 are adapted from Chelton et al (2011) and have been successfully used in the marginal seas (He et al, 2016(He et al, , 2017. Criterion 5 is introduced as an eddy shape error judgment following Kurian et al (2011).…”