1. Remote Sensing Division Naval Research Lab, Washington, DC 20375 Separating Whitecap Fraction of Active Wave Breaking From Satellite Estimates of Total Whitecap Fraction Magdalena D. Anguelova and Paul A. Hwang

2. 20 Feb, 2012Separate active whitecap fraction, Anguelova& Hwang, NRL Enhanced when waves break Surface expression of breaking waves Whitecaps Suitable forcing variable! Air-sea processes and whitecaps Sea spray flux Gas flux Sensible heat flux Latent heat flux Enthalpy flux Momentum flux Dissipation rate Ambient noise Mass Heat Energy 2

3. 20 Feb, 2012 Sea spray flux Gas flux Sensible heat flux Latent heat flux Enthalpy flux Momentum flux Dissipation rate Ambient noise Whitecap fraction Whitecap fraction W The fraction of ocean surface covered with foam Includes all stages of whitecap lifetime Active whitecap fraction W A (zoom image) Foam associated with breaking wave crests Includes only the initial stages of whitecap lifetime The foam moves along with the wave Click image to zoom out 3Separate active whitecap fraction, Anguelova& Hwang, NRL Mass Heat Energy

4. 20 Feb, 2012 Sea spray flux Gas flux Sensible heat flux Latent heat flux Enthalpy flux Momentum flux Dissipation rate Ambient noise Separate active part from the total Photographic measurements : Obtain W or W A Unreliable separation Radiometric measurements: Obtain W W database W variability But, we do not have W A We need to do the next step: New data set W A from W 4Separate active whitecap fraction, Anguelova& Hwang, NRL W W W W WAWA WAWA WAWA WAWA WAWA WAWA Mass Heat Energy

5. 20 Feb, 2012 Physical basis: The concept of breaking crest Breaking crest length distribution: Active whitecap coverage: Energy dissipation: W A (  ) relationship: Expression for from the wave spectrum Integrate over c and obtain: 5Separate active whitecap fraction, Anguelova& Hwang, NRL is breaking fronts velocity

6. 20 Feb, 2012 Evaluate Determine values of T, b, c min, and c max Obtain active whitecap fraction 6Separate active whitecap fraction, Anguelova& Hwang, NRL

7. 20 Feb, 2012 From measured wave spectrum Equilibrium range model Hanson and Phillips (1999) Gulf of Alaska data Parametric approach Hwang and Sletten (2008) Buoy data for T p and H s Validate with measurements Total dissipation rate 7Separate active whitecap fraction, Anguelova& Hwang, NRL 

8. 20 Feb, 2012 Separate swell Hanson and Phillips (2001) Topographic minima method Hwang et al. (2012) Spectrum integration method 8Separate active whitecap fraction, Anguelova& Hwang, NRL Hanson and Phillips (1999) pp Swell Measured spectrum Equilibrium range of wind sea Dimensionless  Dimensionless S(  )

9. 20 Feb, 2012 Parametric approach: Example 9Separate active whitecap fraction, Anguelova& Hwang, NRL ** Other dataset ( Hwang et al, 2011 ) Buoy 41001 mixed Buoy 41001 wind-sea

10. 20 Feb, 2012 Choose values T, b, c min, and c max Breaking parameter Bubbles persistence, where T pw from buoy T p  = 0.2 Mueller and Veron, 2009: W A of Monahan, 1993 T pw influence limited, We would consider other factors: salinity, SST, surfactants T  (0.77 to 2.5) s Breaker speed c min =  c c pw,  c = 0.3 Gemmrich et al., 2008; fully developed sea Others suggest  c  0.8 c min  (1.8 to 5.6) m s -1 c max / c min = 10 10Separate active whitecap fraction, Anguelova& Hwang, NRL pw TT    2 gT c  b = 0.0157

11. 20 Feb, 2012 Active from total whitecap fraction Having W A (  ) from buoy data Make match-ups with W from WindSat 0.5º  0.5º around buoy position Find factor R = W A /W Buoy-satellite match-ups at different latitudes Parameterize R in terms of Wind speed or Geography (lat, lon) Use W database from satellites and R to build W A database 11Separate active whitecap fraction, Anguelova& Hwang, NRL 2006

12. 20 Feb, 2012 Active whitecap fraction Phillips-Buoy 12Separate active whitecap fraction, Anguelova& Hwang, NRL

13. 20 Feb, 2012 Active whitecap fraction Phillips-Buoy 13Separate active whitecap fraction, Anguelova& Hwang, NRL

14. 20 Feb, 2012 Active whitecap fraction Phillips-Buoy 14Separate active whitecap fraction, Anguelova& Hwang, NRL

15. 20 Feb, 2012 Active whitecap fraction Phillips-Buoy 15Separate active whitecap fraction, Anguelova& Hwang, NRL

16. 20 Feb, 2012 Sensitivity to value choices 16Separate active whitecap fraction, Anguelova& Hwang, NRL

17. 20 Feb, 2012 Sensitivity to choice of c min 17Separate active whitecap fraction, Anguelova& Hwang, NRL

18. 20 Feb, 2012 Sensitivity to value choices 18Separate active whitecap fraction, Anguelova& Hwang, NRL

19. 20 Feb, 2012 Sensitivity to choice of T 19Separate active whitecap fraction, Anguelova& Hwang, NRL

20. 20 Feb, 2012 Sensitivity to choice of b 20Separate active whitecap fraction, Anguelova& Hwang, NRL

21. 20 Feb, 2012 Ratio W A /W 21Separate active whitecap fraction, Anguelova& Hwang, NRL

22. 20 Feb, 2012 Summary Obtain W A from W on a global scale using satellite data Phillips concept to obtain W A from dissipation rate  Buoy data for wave spectrum Isolate swell Parametric approach to obtain  Choose values for coefficient of proportionality Calculate W A (  ) Obtain factor W A / W Future work: Validate  with independent measurements, previous and new Refine choices for T, b, c min, and c max /c min Extend W A calculations for more latitudes Parameterize W A / W 22Separate active whitecap fraction, Anguelova& Hwang, NRL

23. 20 Feb, 201223Separate active whitecap fraction, Anguelova& Hwang, NRL Click image to zoom in Wind direction WAWA W Photo courtesy of Prof. William M. Drennan, RSMAS, Miami

24. 20 Feb, 2012 Breaking parameter b 24Separate active whitecap fraction, Anguelova& Hwang, NRL b = 0.0157