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SURFACE WAVE EFFECTS ON THE OCEAN MIXED LAYER RESPONSE TO HURRICANE BONNIE

SURFACE WAVE EFFECTS ON THE OCEAN MIXED LAYER RESPONSE TO HURRICANE BONNIE. T. M. Cook, L. K. Shay, S. D. Jacob, C. Wayne Wright, P.G. Black, E. W. Uhlhorn. Goal: To understand the role of the surface wave swell on the response of the oceanic mixed layer.

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SURFACE WAVE EFFECTS ON THE OCEAN MIXED LAYER RESPONSE TO HURRICANE BONNIE

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  1. SURFACE WAVE EFFECTS ON THE OCEAN MIXED LAYER RESPONSE TO HURRICANE BONNIE T. M. Cook, L. K. Shay, S. D. Jacob, C. Wayne Wright, P.G. Black, E. W. Uhlhorn Goal: To understand the role of the surface wave swell on the response of the oceanic mixed layer. Research support by NSF, NASA, NOAA. Aircraft support provided by NOAA AOC.

  2. INTRODUCTION: • During strong forcing events, SSTs mix with oceanic mixed layer and upper thermocline. • Low-frequency surface waves induce an orbital velocity in the OML that has a e-kz where k is the dominant wavenumber (Sanford et al. 1987). • Huang (1981) linked OML deepening to SW slope (Hs/wavelength) under moderate winds. • Bonnie Measurements from 24 Aug 1998 (AXBTs, GPS) will be related to the surface wave fields from the SRA (Wright et al., 2001).

  3. Huang’s Approach: • Significant Slope: j = H l-1 • Mixing Efficiency: mo = f(h,Co u*-1, j) • Dissipation: e = f(Co u*-1, j) • Mixing efficiency is term that multiplies the surface friction velocity of the water (w*3). • Values for this term range from 0.2 to 50 (a factor of 100) depending on the OML model. • What is the role of surface wave processes on the OML in storms?

  4. Bonnie Track and Oceanic Heat Content Loss From Radar Altimeter Bonnie Track and Oceanic Heat Content Loss From Radar Altimeter

  5. HURRICANE BONNIE WIND FIELD (Courtesy of M. Powell): HURRICANE BONNIE WIND FIELD (Courtesy of M. Powell):

  6. Directional Wave Spectra From SRA: Directional Wave Spectra From SRA:

  7. Cd x 10-3

  8. Wind Stress/Ekman Pumping Velocity

  9. ROTHr Surface Current and Vorticity Field (Jack Harlan, ETL)

  10. D MLT and D MLD From AXBTs and Climatology

  11. Hs and j from SRA:

  12. DMLT and DMLDversus j (Stokes Limit of 0.0505):

  13. Wave Age (u*co-1)

  14. Surface Wave-Induced Orbital Velocity:2-Speed AXCPs (Sanford et al. )

  15. RESEARCH SUMMARY: • Results suggest a relationship between surface slope (j) and OML cooling and HC loss. • SRA needs to be complemented with Current Shear field from AXCPs and TKE from OML Floats (D’Asaro, 2002). • Langmuir Cells (wave-induced orbital velocities and wind-driven current shear) may provide the link in TKE redistribution occurs over short time/space scales (15-20 min, < km).

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