AirSea Interaction: Physics of airsurface interactions and coupling to oceanatmosphere BL processes

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Air-Sea InteractionPhysics of air-surface
interactions and coupling to ocean/atmosphere BL
processes

• Emphasize surface fluxes
• Statement of problem
• Present status
• Parameterization issues
• An amusing case

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Flux Definitions
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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

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Physically-Based Parameterizations
Old Days CE1E-3 and k0.003U2 and
sprayS(r)fwhitecap
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Historical perspective on turbulent
fluxesTypical 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) .
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• 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.

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

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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

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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

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Turbulent Fluxes at High Winds
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Strong wind turbulent fluxes

• Direct turbulent fluxes
• Cd or Charnock coeff
• Ch/Ce or zot/zoqf(Rr)
• Droplet mediated fluxes
• Momentum lt?wugt
• Mass flux lt?wgt
• Enthalpy flux partitioning Qs and Ql

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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 (?ltwugt Andreas Droplet
stability effect (ltw ?gt - Makin
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• 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
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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.
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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

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Original Droplet EquationsFairall/Andreas circa
1990
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Sn Surface Source Strength for Sea Spray Droplets
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Droplet Source Functions
Fairall et al. 1994
Fairall, Banner, Asher Physical Model
P energy wave breaking s surface tension r
droplet radius ? Kolmogorov microscale f
fraction of P going into droplet
production Vfdroplet mean fall velocity
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Feedback
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Partitioning of Droplet ContributionStages 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 QseQsQl_a
• Enthalpy Bowen ratio Qs/Ql_a(To-Ta)/(Ta-Twet)
• QsQsebowen/(1bowen)

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Feedback Characterization dTa
Effect on the fluxes
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Turbulent Fluxes Above the Droplet Evaporation
Layer
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Direct Transfer Coefficients Assumed in
Parameterization
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Ratio of Transfer Coefficients With Droplet
Enthalpy Flux
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Feedback SensitivitySource Strength0.3
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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

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Simulation with GFDL Operational Model Isabel
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ButSimulations with New Cd and Ce/Ch
Old Cd Ce/Ch
New Cd Ce/Ch