Nonlocal dispersion in the Gulf of Mexico

Pair-separation statistics of surface drifters launched in the Grand LAgrangian Deployment (GLAD) in the northern Gulf of Mexico are investigated. Diverse measures of the dispersion are calculated and compared to the second-order structure function, used to infer the kinetic energy spectrum. The measures indicate nonlocal pair dispersion (in which separations grow exponentially in time), from separations of 0.3 km to the Rossby deformation radius, about 50 km. However, the structure function increases as r^2/3, indicating that the energy spectrum is proportional to k^-5/3. The difference originates from inertial oscillations, which affect the energy spectrum but have little impact on the dispersion.