Effect of swell on wind stress for light to moderate winds

Charles L. Vincent, Hans C. Graber, Clarence O. Collins

Research output: Contribution to journalArticlepeer-review


Buoy observations from a 1999 Gulf of Mexico field program (GOM99) are used to investigate the relationships among friction velocity u∗, wind speed U, and amount of swell present. A U-u∗sea parameterization is developed for the case of pure wind sea (denoted by u∗sea), which is linear in U over the range of available winds (2-16ms-1). The curve shows no sign of an inflection point near 7-8ms-1 as suggested in a 2012 paper by Andreas et al. on the basis of a transition from smooth to rough flow. When observations containing more than minimal swell energy are included, a different U-u∗ equation for U < 8ms-1 is found, which would intersect the pure wind-sea curve about 7-8ms-1. These two relationships yield a bilinear curve similar to Andreas et al. with an apparent inflection near 7-8ms-1. The absence of the inflection in the GOM99 experiment pure wind-sea curve and the similarity of the GOM99 swell-dominated low wind speed to Andreas et al.'s low wind speed relationship suggest that the inflection may be due to the effect of swell and not a flow transition. Swell heights in the range of only 25-50 cm may be sufficient to impact stress at low wind speeds.

Original languageEnglish (US)
Pages (from-to)3759-3768
Number of pages10
JournalJournal of the Atmospheric Sciences
Issue number11
StatePublished - Nov 2020
Externally publishedYes


  • Atmosphere-ocean interaction
  • Sea state

ASJC Scopus subject areas

  • Atmospheric Science


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