Air-Sea Interaction: Physics of air-surface interactions and coupling to ocean/atmosphere BL processes

Transcription

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 3/25/2008 1

2 3/25/ Flux Definitions p l s nl ns net H H H R R H Heat Net + = : ) ( : ˆ ˆ : : : wet s pw p y a x a e a l pa a s T T P c H Rain Heat j w u i w u Stress w T L H Heat Latent w T c H Sensible Heat = + = = = ρ ρ τ ρ ρ e a l w L H P E P F Water ρ / : = = ) ( ) ( ) ( : : ) ( / : / 0.61 / : r n w r n w r w n F Exchange Particle w r F Gas Exchange P E g c gh F Water L H T c H F Air s g n x x pw w net b e a l pa a s b + = = + = + = β ρ α ρ ρ

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 Met Flux : w x = CxU ( X s X r ) = CxU X Gas Flux : w x = kxα x X α = sol. Particles : F = V ( r) n( r) ; F deposition source = F( f d whitecap, U, u*, wave breaking, slope) 3/25/2008 3

4 3/25/ Physically-Based Parameterizations 2 )]/ ) / ( ) ( ( ][1 ) ( 4 9 exp[ ) ( 3 4 : ] 2 ) / ln( 5 [ )] / ln( [ / ] / [ : )] / ( ) / )][ln( / ( ) / [ln( )] ( ) ( [0.98* ] ) ( ) ( [ : 4 / / 2 1/ 2 1/ * 2 1/ 2 2 * u g s ca d ca a x w rw cw w a w ar x wr a x x q oq u o s sat meso y x Slope r W h U erf r a l f r n r Spray Droplet Sea S C S h z S h X X u w r Gas Flux L z z z L z z z z q T q U W U U w q Flux Met σ πη σ π κ α δ ρ ρ α α ψ ψ γ β κ + Ε = = = & Old Days: C E =1E-3 and k=0.003*u 2 and spray=s(r)*f whitecap

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 3/25/2008 (long-dashed lines). 5

6 3/25/2008 6

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 ( ); the dashed line the original NCEP model. 3/25/2008 7

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9 CO2 Flux: Transfer velocity versus wind speed Hare, McGillis, Edson, Fairall Work under way on DMS and Ozone 3/25/2008 9

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 ( micron) Principally breaking-wave spume production No measurements at high winds Order of magnitude uncertainty 3/25/

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 3/25/

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) z o 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 3/25/

13 Turbulent Fluxes at High Winds 3/25/

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 3/25/

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 3/25/

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: 1) 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. EM-APEX day 250 3/25/

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 = stressair and so this is the null model with respect to some of the most interesting effects of surface waves. 3/25/

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19 A Sea-Spray Thermodynamic Parameterization Including Feedback C. W. Fairall *, J-W. Bao, and J. Wilczak NOAA Environmental Technology Laboratory (ETL) Boulder, CO 1. Background 2. Source strength 3. Feedback 4. Sensitivities 5. Model tests 3/25/

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21 H = ρ c C U ( T T ) s a pa H o a Original Droplet Equations Fairall/Andreas circa 1990 H = ρ L C U ( q ( T ) q ) Q l a e E s o a = ρ L F l w e E Q = ρ c F ( T T ) s w pw v o a Fv = 3 4π / 3 r Sn ( r) dr f FE = τ 3 π / r Sn ( r) dr τ r 3/25/

22 S n Surface Source Strength for Sea Spray Droplets 3/25/

23 Droplet Source Functions Fairall et al S = f ( U) S ( r) n no. f ( U ) = W = U 3 4 b Fairall, Banner, Asher Physical Model 3 4πr f Pr α πη U( h) V f / Slope S n ( r ) exp[ ( ) / = ]*[ 1 + erf ( )] / 2 3 σl 4 r σ P energy wave breaking σ surface tension r droplet radius η Kolmogorov microscale f fraction of P going into droplet production V f =droplet mean fall velocity 3/25/ u

24 Feedback 3/25/

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) 3/25/

26 Feedback Characterization δt a 1 β δ β δ 1 β Ta = Td = feed *( Ta Tw ) = feed * ( 1 s) γ feed = Ql Q+ ( H + Q + H ) / feed_ tune l s se sε Effect on the fluxes: H = ρ L C U[ T ( T δt )] s a e E o a a H = ρ L C U[ q ( T ) q ( T + δt )] l a e E s o s d d Q = ρ c F ( T T ) se w pw v o w Q = ρ L G( U ) hβ( T )[ q ( T δt ) q ( T + δt )] lb w e o s a a s d d 3/25/

27 Turbulent Fluxes Above the Droplet Evaporation Layer H s_ tot = H s + Qs + H sε Qlb = H s + ρc pchuδt f + Qs + H sε αql Hl _ tot = Hl + Qla + Qlb = Hl ρleceuδqa + Qla + αql 3/25/

28 Direct Transfer Coefficients Assumed in Parameterization x C d, C k U 10 (m/s) 3/25/

29 Ratio of Transfer Coefficients With Droplet Enthalpy Flux 2.8 Feedtune=0.3, 1.0, source= C d /C k source= U 10 (m/s) 3/25/

30 Feedback Sensitivity: Source Strength=0.3 3/25/

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 3/25/

32 Simulation with GFDL Operational Model: Isabel 3/25/

33 But: Simulations with New Cd and Ce/Ch New Cd Ce/Ch Old Cd Ce/Ch 3/25/