Horizontal nearshore surface dispersion for the Florida Panhandle

Abstract

Knowledge of how a buoyant tracer is horizontally dispersed in the nearshore environment is important for a variety of applications, from aiding oil-spill cleanup strategies to detecting drifting mines. Horizontal nearshore surface dispersion for the Florida panhandle was investigated using 75 drifters deployed over a five-day period during the Surfzone Coastal Oil Pathways Experiment (SCOPE) in December 2013. The data set consisted of 382 original drifter pairs in the spatial range of ~ 5 m to ~ 4.5 km with drifter position sampled every 1 sec for a duration of ~ 30 – 40 hours. Lagrangian flow descriptions revealed that the drifters moved coherently with the majority of drifter trajectories correlated with the surface current forced by the local wind field. The horizontal dispersion estimate was quantified using two-particle statistics, D2, and Finite Scale Lyapunov Exponent, λ, methodologies. D2 results revealed a generally ballistic, D2 ~ t2, path-followed regime, with λ results exhibiting enhanced growth over scales < 100 m, with Richardson like growth, λ ~ δ-2/3, for scales > 100 m. It is conjectured that the mechanisms responsible for influencing the horizontal nearshore surface dispersion for the Florida panhandle are complex and likely a combination of mechanisms from small-scale coherent motions to shear, but predominately being forced by the surface current induced by the local wind field. Variability in D2 values is attributed to the orientation change of the drifter trajectories coupled with the variability in the wind field.