Abstract's details
Detecting Mekong River plume fronts using SWOT altimetry and drifter observations
Event: 2025 SWOT Science Team Meeting
Session: Deltas, Estuaries and Coasts
Presentation type: Poster
The dynamics of the Mekong river plume, one of the largest river systems in Southeast Asia, is investigated using the data from the Surface Water and Ocean Topography (SWOT) satellite mission, complemented by surface drifter observations collected during PLUME oceanographic campaign in June 2024. We employ a variational method of velocity interpolation to reduce the impact of errors propagating through the derivatives of SWOT sea surface height (SSH) which often appears noisy, affected by gaps and small-scale artifacts. The complexity of the SSH signal arises from large buoyancy input supplied by multiple estuaries which generates highly dynamic regional circulation in this shallow water region, further influenced by strong wind forcing.
The velocity field obtained through variational interpolation is not in geostrophic balance but likely provides a synoptic view of unbalanced mesoscale motions. This conclusion is supported by comparisons with velocities obtained from 16 surface drifter trajectories and acoustic Doppler current profiler (ADCP) measurements. The analysis of SWOT-derived velocities revealed consistent surface circulation patterns and indicated the presence of submesoscale frontal structures within the plume body. The frontal zone identification method is based on the extraction of Lagrangian Coherent Structures (LCS) from the surface velocity field using finite-size Lyapunov exponents (FSLE). Large values in the attracting FSLE field (ridge lines) enable the identification of zones of enhanced shear along outflowing manifolds, which are crucial for understanding plume dynamics and mixing within the plume body. FSLE ridge lines revealed diverse geometries of frontal zones, such as semi-spherical or hook-like shapes, and enabled characterization of plume morphology and its offshore expansion. The convergence of real drifters within frontal zones identified from SWOT measurements provides evidence that, in the study region, SWOT-derived velocities at the submesoscale are not in geostrophic balance. This has promising implications for future assessments of horizontal dispersion, vertical motions, and mixing processes in river plume systems which have major ecological and economic importance in coastal ocean regions.
The velocity field obtained through variational interpolation is not in geostrophic balance but likely provides a synoptic view of unbalanced mesoscale motions. This conclusion is supported by comparisons with velocities obtained from 16 surface drifter trajectories and acoustic Doppler current profiler (ADCP) measurements. The analysis of SWOT-derived velocities revealed consistent surface circulation patterns and indicated the presence of submesoscale frontal structures within the plume body. The frontal zone identification method is based on the extraction of Lagrangian Coherent Structures (LCS) from the surface velocity field using finite-size Lyapunov exponents (FSLE). Large values in the attracting FSLE field (ridge lines) enable the identification of zones of enhanced shear along outflowing manifolds, which are crucial for understanding plume dynamics and mixing within the plume body. FSLE ridge lines revealed diverse geometries of frontal zones, such as semi-spherical or hook-like shapes, and enabled characterization of plume morphology and its offshore expansion. The convergence of real drifters within frontal zones identified from SWOT measurements provides evidence that, in the study region, SWOT-derived velocities at the submesoscale are not in geostrophic balance. This has promising implications for future assessments of horizontal dispersion, vertical motions, and mixing processes in river plume systems which have major ecological and economic importance in coastal ocean regions.
Contribution: ST2025DEC2-Detecting_Mekong_River_plume_fronts_using_SWOT_altimetry_and_drifter_observations_.pdf (pdf, 3725 ko)
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