Figure 9. Climatological Lagrangian Coherent Structures (cLCS) at the western Caribbean Sea. Colors indicate the strength of attraction, with red indicating the strongest attraction of nearby parcels; white indicates isolated regions or low stirring activity. Panel (a) are the annual and (b) the monthly cLCS for the Caribbean basin and the Yucatan Peninsula region, respectively.
The persistence of strong cLCS throughout the year efficiently prevents particles from reaching zone 2 without the influence of wind (Figure 8). However, the isolation of region 2 changes with the wind: some particles enter zone 2 with 1% windage, and considerably more enter zone 2 with 2% windage (Figure 8). The persistent Yucatan Current transport barrier is debilitated when cLCS are computed with currents plus 1% windage, and it is completely erased when cLCS are computed with currents plus 2% windage (Figure 10). Also notable is that with 2% windage, the zone 4 cLCS tend to converge while directing towards the Mexican coast from about 84oW to 86oW in the vicinity of 18oN, a feature absent in the cLCS computed from only currents (Figure 10, cf. left and right panels). Independent experiments using an instantaneous velocity from HYCOM by Lara-Hernández et al. (2023) show that with 2% windage, trajectories reaching the Mexican Caribbean coast move along these strongly attracting cLCS while approaching the coast and then spread along the coastline (Text S2 and figure S6). This constitutes an additional independent confirmation that cLCS identifies and extracts the predominant transport patterns from the instantaneous velocity.