Submesoscale evolution of surface drifter triads in the Gulf of Mexico

Triangle shape metrics are analyzed to quantify the evolution of submesoscale (100-500 m initial separation) surface drifter triplets released in the northern Gulf of Mexico. The observations are compared to synthetic drifters advected by geostrophic velocity fields derived from satellite altimetry. Observed submesoscale triads evolve rapidly, reaching highly elongated configurations on timescales of 6 h to 2 days, in contrast to 6 days or longer for altimetry-derived synthetic data. Estimates of horizontal divergence and strain rate from the drifter triplets indicate the relative importance of divergence in the evolution of triangle shape. Horizontal divergence is scale dependent, on the order of the local Coriolis parameter, and 2 to 3 times larger for initial 100 m scales compared to initial 500 m scales.