Observations of Air-Sea Momentum Flux Variability Across the Inner Shelf

David G. Ortiz-Suslow, Brian K. Haus, Neil J. Williams, Hans C. Graber, Jamie H. MacMahan

Research output: Contribution to journalArticlepeer-review

3 Scopus citations

Abstract

Over the open ocean, the aerodynamic drag coefficient is typically well predicted; however, the impact depth-limited processes have on the drag remains underexplored. A case study is presented here where winds, waves, and currents were simultaneously observed from a mobile platform that repeatedly transected the inner shelf of Monterey Bay, CA. Eddy covariance-derived drag coefficients were compared to several bulk parameterizations, including all of the roughness variations of COARE 3.5 and two explicitly depth-limited models. The analysis demonstrated that the drag was underestimated by O(2–4) times and the variability with wind speed or cross-shore distance was not well predicted. The drag based on a recent depth-limited roughness length model performed substantially better than the rest of the bulk estimates, which were all within 15% of each other and effectively equivalent given typical operational uncertainties. The measured friction velocity was compared to a wave-dependent parameterization and generalizing the model to arbitrary water depth significantly improved the mean observation-model difference to within 30%. Latent variability in the observation-model comparison was associated with stability, wind direction, and wave steepness. The wind stress angle variability was also analyzed. Stress veering was correlated with the alongshore surface current within 2 km from shore (r 2 = 0.7–0.95, p < 0.05); offshore of this margin, consistent wind stress veering was observed and may be attributable to a secondary, low-frequency swell system. These results demonstrate that it remains a persistent challenge to accurately predict wind stress variability in the nearshore, especially at locations with complex wave and current fields.

Original languageEnglish (US)
Pages (from-to)8970-8993
Number of pages24
JournalJournal of Geophysical Research: Oceans
Volume123
Issue number12
DOIs
StatePublished - Dec 2018

Keywords

  • Monterey Bay
  • air-sea interaction
  • field measurements
  • inner shelf
  • nearshore processes
  • shoaling waves

ASJC Scopus subject areas

  • Geochemistry and Petrology
  • Geophysics
  • Earth and Planetary Sciences (miscellaneous)
  • Space and Planetary Science
  • Oceanography

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