Statistics of simulated and observed pair separations in the Gulf of Mexico

TL;DR

This study compares pair-separation statistics of in-situ drifters and NCOM model simulations in the Gulf of Mexico, revealing differences in dispersion behaviors influenced by inertial oscillations and launch configurations.

Contribution

It provides a detailed comparison of observed and simulated surface drifter dispersion, highlighting the impact of inertial oscillations and launch strategies on dispersion statistics.

Findings

NCOM pairs show nonlocal dispersion at small scales.

GLAD drifters exhibit local, power-law dispersion growth.

Inertial oscillations significantly influence small-scale energy levels.

Abstract

Pair-separation statistics of in-situ and synthetic surface drifters deployed near the \emph{Deepwater Horizon} site in the Gulf of Mexico are investigated. The synthetic trajectories derive from a 1-km-resolution data-assimilative Navy Coastal Ocean Model (NCOM) simulation. The in-situ drifters were launched in the Grand LAgrangian Deployment (GLAD). Diverse measures of the dispersion are calculated and compared to theoretical predictions. For the NCOM pairs, the measures indicate nonlocal pair dispersion at the smallest sampled scales. At separations exceeding 100 km, pair motion is uncorrelated, indicating absolute rather than relative dispersion. With the GLAD drifters however the statistics suggest local dispersion (in which pair separations exhibit power law growth), in line with previous findings. The disagreement stems in part from inertial oscillations, which affect the energy levels at small scales without greatly altering the net particle displacements. They were significant in GLAD but much weaker in the NCOM simulations. In addition the GLAD drifters were launched close together, producing few independent realizations and hence weaker statistical significance. Restricting the NCOM set to those launched at the same locations yields very similar statistics.