Small-scale dispersion in the presence of langmuir circulation

Henry Chang, Helga S. Huntley, A. D. Kirwan, Daniel F. Carlson, Jean A. Mensa, Sanchit Mehta, Guillaume Novelli, Tamay M. Özgökmen, Baylor Fox-Kemper, Brodie Pearson, Jenna Pearson, Ramsey R. Harcourt, Andrew C. Poje

Research output: Contribution to journalArticlepeer-review

8 Scopus citations


We present an analysis of ocean surface dispersion characteristics, on 1-100 m scales, obtained by optically tracking a release of O(600) bamboo plates for 2 hours in the Northern Gulf of Mexico. Under sustained 5-6 m/s winds, energetic Langmuir cells are clearly delineated in the spatially dense plate observations. Within 10 minutes of release, the plates collect in windrows with 15 m spacing aligned with the wind. Windrow spacing grows, through windrow merger, to 40 m after 20 minutes and then expands at a slower rate to 50 m. The presence of Langmuir cells produces strong horizontal anisotropy and scale dependence in all surface dispersion statistics computed from the plate observations. Relative dispersion in the crosswind direction initially dominates but eventually saturates, while downwind dispersion exhibits continual growth consistent with contributions from both turbulent fluctuations and organized mean shear. Longitudinal velocity differences in the crosswind direction indicate mean convergence at scales below the Langmuir cell diameter and mean divergence at larger scales. Although the secondorder structure function measured by contemporaneous GPS-tracked surface drifters drogued at ~ 0:5 m shows persistent r2=3 power law scaling down to 100-200 m separation scales, the second-order structure function for the very near surface plates observations has considerably higher energy and significantly shallower slope at scales below 100 m. This is consistent with contemporaneous data from undrogued surface drifters and previously published model results indicating shallowing spectra in the presence of direct windwave forcing mechanisms.

Original languageEnglish (US)
Pages (from-to)3069-3085
Number of pages17
JournalJournal of Physical Oceanography
Issue number10
StatePublished - Oct 2019
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Oceanography


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