Advancements in Air-Sea Interaction: Surface Fluxes and Parameterization

1. Air-Sea Interaction:Physics of air-surface interactions and coupling to ocean/atmosphere BL processes • Emphasize surface fluxes • Statement of problem • Present status • Parameterization issues • An amusing case

2. Flux Definitions

3. Present Status of Surface Flux Parameterizations • P: No dependence on surface variables • Radiation: Depends on albedo, emissivity, and Ts but real problem is clouds • Turbulent Fluxes: Bulk Parameterization

4. Physically-Based Parameterizations Old Days: CE=1E-3 and k=0.003*U2 and spray=S(r)*fwhitecap

5. Historical perspective on turbulent fluxes:Typical moisture transfer coefficients Algorithms of UA (solid lines), COARE 2.5 (dotted lines), CCM3 (short-dashed lines), ECMWF (dot-dashed lines), NCEP (tripledot-dashed lines), and GEOS (long-dashed lines) .

7. Air-Sea transfer coefficients as a function of wind speed: latent heat flux (upper panel) and momentum flux (lower panel). The red line is the COARE algorithm version 3.0; the circles are the average of direct flux measurements from 12 ETL cruises (1990-1999); the dashed line the original NCEP model.

9. CO2 Flux: Transfer velocity versus wind speedHare, McGillis, Edson, Fairall Work under way on DMS and Ozone

10. Particle Fluxes • Optically relevant (.1 – 10 micron): • Principally whitecap-bubble production • Measurement and interpretation problems • Some dependence on laboratory work • No consensus • Thermodynamically relevant (50-500 micron) • Principally breaking-wave spume production • No measurements at high winds • Order of magnitude uncertainty

11. Progress in Last 5ish Years • Conventional turbulent fluxes: • Greatly expanded data base • 5% 0-20 m/s • Progress on wind-wave-stress models • M-O stability functions, light-wind convective & stable • Gas Fluxes: • Ship-based covariance measurements • Physically-based parameterization • Particle Fluxes: • Expanded modeling efforts

12. Flux Parameterization Issues • Representation in GCM • Except for P, most observations are point time averages • Concept of gustiness sufficient? • Mesoscale variable? Precip, convective mass flux, … • Strong winds • General question of turbulent fluxes, flow separation, wave momentum input • Sea spray influence • Waves • Stress vector vs wind vector (2-D wave spectrum) • zo vs wave age & wave height • Breaking waves • Gas and particle fluxes • Distribution of stress and TKE in ocean mixed layer (P. Sullivan) • Gas fluxes • Bubbles • Surfactants (physical vs chemical effects) • Extend models to chemical reactions • Particle fluxes • Interpretation of measurements • Source vs deposition

13. Turbulent Fluxes at High Winds

14. Strong wind turbulent fluxes • Direct turbulent fluxes • Cd or Charnock coeff • Ch/Ce or zot/zoq=f(Rr) • Droplet mediated fluxes • Momentum <ρwu> • Mass flux <ρw> • Enthalpy flux; partitioning Qs and Ql

15. Evidence • Strom surge models • Cd/Ck ratio, Emanuel • Powell drop sonde profiles • Price ocean mixed layer integrations • Laboratory simulations Explanations Slippery young waves (direct Cd) – Moon et al Droplet mass effect (ρ<w’u’>– Andreas Droplet stability effect (<w’ ρ’> - Makin

16. GOES SST imagery. Daily composites made from hourly images. GOES seems • to be the most prolific SST imaging system, though at the expense of accuracy and • noise level. • SST cooling in these images exhibits: • Significant horizontal structure, i) a marked rightward bias, ii) along-track • variability that is not correlated with intensity, and, • 2) A rapid relaxation back toward pre-storm SST, e-folding approx 10 days. day 250 EM-APEX 1634 1633 1636

17. A numerical simulation of the UO response The numerical ocean model is Price et al., '94; grid-level, high resolution, closed with PWP upper ocean mixing algorithm. The ocean IC is from pre-Frances EM-APEX. The single most important thing is the hurricane stress field: a fit to HWINDS for the wind field and Powell et al. for the drag coefficient. The implicit assumption is that stressocean= stressairand so this is the null model with respect to some of the most interesting effects of surface waves.

19. A Sea-Spray Thermodynamic Parameterization Including Feedback C. W. Fairall *, J-W. Bao, and J. WilczakNOAA Environmental Technology Laboratory (ETL)Boulder, CO • Background • Source strength • Feedback • Sensitivities • Model tests

21. Original Droplet EquationsFairall/Andreas circa 1990

22. Sn Surface Source Strength for Sea Spray Droplets

23. Droplet Source Functions Fairall et al. 1994 Fairall, Banner, Asher Physical Model P energy wave breaking σ surface tension r droplet radius η Kolmogorov microscale f fraction of P going into droplet production Vf=droplet mean fall velocity

24. Feedback

25. Partitioning of Droplet Contribution:Stages of cooling/evaporation • Simplification: consider large droplets that are ejected, cool to wet bulb temperature and re-enter ocean with negligible change in mass • Stages: • Cool from To to Tair = Qs • Cool from Tair to Twet = Ql_a • Evaporation while at Twet = Ql_b • Total droplet enthapy transfer Qse=Qs+Ql_a • Enthalpy Bowen ratio = Qs/Ql_a=(To-Ta)/(Ta-Twet) • Qs=Qse*bowen/(1+bowen)

26. Feedback Characterization δTa Effect on the fluxes:

27. Turbulent Fluxes Above the Droplet Evaporation Layer

28. Direct Transfer Coefficients Assumed in Parameterization

29. Ratio of Transfer Coefficients With Droplet Enthalpy Flux

30. Feedback Sensitivity:Source Strength=0.3

31. Model Tests (Bao and Ginis) • IVAN, ISABEL • GFDL operational • GFDL new zo, zt • WRF • PLANS • HWRF at high resolution – matrix of tune values • Explicit droplet model (Kepert/ Fairall) in HWRF • Coordinate with Penn State LES work

32. Simulation with GFDL Operational Model: Isabel

33. But:Simulations with New Cd and Ce/Ch Old Cd Ce/Ch New Cd Ce/Ch