Magdalena D. Anguelova

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Novel Applications of Remote Sensing for
Improved Quantification of Sea Spray Source
Function

• Magdalena D. Anguelova
• Michael H. Bettenhausen
• William F. Johnston
• Peter
  W. Gaiser

Remote Sensing Division, Naval Research
Laboratory, Washington, DC Computational
Physics, Inc., Springfield, VA
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Motivation

• Sea spray aerosols
• Direct effect cooling
• Indirect effect
• Dominate the activation of CCN
• Compete with SO42- aerosols
• Halogen chemistry
• Reactive Cl and Br
• Tropospheric O3
• Sink of S
• Sea spray droplets
• Heat exchange
• Tropical storm intensification

• Whitecaps
• Gas exchange
• Ocean albedo roughness
• Geophysical retrievals
• Surface wind
• Ocean color
• Salinity

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Sea spray source function
Rate of production of sea spray per unit area per
increment of droplet radius, r (s-1 m-2 ?m-1).
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Possible improvements
de Leeuw et al. ODowd et al. Keene et al. Quinn
Bates et al. Meskhidze Peters et al.

• For the size distribution f(r)
• Extend the size range, large and small ends
• Recognize and include the effect of organics
• Introduce ambient factors
• For the scaling factor f(U)
• Less uncertainty in measuring W
• Introduce ambient factors
• Remote sensing method, results, implications

(de Leeuw et al., 2011)
Ernie Lewis poster Sofiev et al., 2011
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Objective

• Measure W globally
• Compile database
• Model the high variability of whitecap fraction

U wind speed (U10 or u) ?T atmospheric
stability ( Tair Tsea) X wind fetch d
wind duration Ucur water currents Ts sea
surface temperature S salinity Ck
concentration, type (k) of surface active
materials
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Whitecaps signature
High Reflectivity
High Emissivity
Reflectivity Emissivity
IR
mW
Vis
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Remote sensing of sea foam

• Microwave region
• Advantages
• Transparent (almost) atmosphere
• ...4 problem ...at 5 GHz,..., 90 problem at
  IR (Swift, 1990)
• Tractable atmospheric correction
• Clouds penetration
• Drawback
• Low resolution
• Smoother geophysical variability
• Trade-off global coverage
• More data
• Various conditions

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Models
Anguelova and Webster, 2006 Anguelova et al., 2006

• Rough sea surface model
• 2-scale
• Wave spectrum
• Durden/Vesecky/Yueh
• Tuned for roughness only
• Using WindSat code (v. 1.9.6)
• Foam emissivity model
• RT model
• Layer with vertically non-uniform properties
• Distribution of thicknesses

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Data

• Independent sources
• TB from WindSat
• V, L from SSM/I or TMI
• U10 and ? from QuikSCAT or GDAS
• Ts from GDAS
• S 34 psu
• Trade-off
• Sampling issues
• Use long-term data

Sample count
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Estimates of W

• Improvements over the feasibility study
  (Anguelova and Webster, 2006)
• More physical models
• Independence of the variables

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Compare to photographic data
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Further development

• Models
• Higher resolution
• Improved wave spectrum in 2-scale model
• Comparisons/Validation
• More points for direct comparisons
• Indirect comparisons in terms of other variables
• CO2 fluxes from ship cruises
• and COARE CO2 parameterization
• AOD from AERONET
• and AOD from microphysical aerosol model
• Uncertainty characterization
• Currently uncertainty minimization
• Evaluate the remaining using global geophysical
  model

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Whitecaps data base

• All available orbits for
• Resolution 5070 km2
• Time period
• Entire 2006
• Months of 2003, 2007 and 2008
• Gridded data
• With 0.5? x 0.5? grid box
• Any other N? x N? possible
• Time periods
• Daily
• Monthly
• Weekly (7 days)
• 3-days

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Geographic characteristics of W
March, 2007 0.5? x 0.5?
Wind speed formula
Satellite, 10.7 GHz, H pol.
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Geographic characteristics of W
March, 2007 0.5? x 0.5?
Wind speed formula
Satellite, 18.7 GHz, H pol.
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Develop parameterization(s)

• Relative importance of the variables
• Correlation analysis

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New sea spray source function

• Include wave-field characteristics and one more
  factor
• Improve/choose size distribution
• Include organics

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Sea-salt flux
Anguelova and Webster, 2006

• Solar irradiance at TOA (W/m2) GCM ERBE
• NO aerosols
• Max difference over the oceans.

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Sea foam definition

• Passive remote sensing
• Radiometers detect only the surface foam layers
• Skin depth
• At microwave frequencies
• a few mm to a few cm

• Oceanographic definition
• Whitecaps on the surface
• Bubble plumes below

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Photographic measurements

• High uncertainty up to 30 or more
• Intensity threshold
• A and B stages under oblique angle
• Patchy coverage
• Open ocean
• Southern ocean!

Stramska and Petelski, 2003
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Improvements and restrictions
(de Leeuw et al., 2011)
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Modeling whitecap fraction