Magdalena D. Anguelova Michael H. Bettenhausen William F. Johnston* Peter W. Gaiser Novel Applications of Remote Sensing for Improved Quantification of Sea Spray Source Function Remote Sensing Division, Naval Research Laboratory, Washington, DC * Computational Physics, Inc., Springfield, VA

Motivation  Sea spray aerosols  Direct effect – cooling  Indirect effect  Dominate the activation of CCN  Compete with SO 4 2- aerosols  Halogen chemistry  Reactive Cl and Br  Tropospheric O 3  Sink of S  Sea spray droplets  Heat exchange  Tropical storm intensification  Whitecaps  Gas exchange  Ocean albedo & roughness  Geophysical retrievals  Surface wind  Ocean color  Salinity Photo courtesy of C. Fairall 6 Dec, 20112Whitecaps and sea spray, Anguelova et al., NRL

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 ). )f() rU   dr bardF,...,, From photographic measurements (Monahan and O’Muircheartaigh, 1980) From measurements using various methods )()(fUUWU    log f )(f rd r d r  6 Dec, 20113Whitecaps and sea spray, Anguelova et al., NRL Size distributionScaling factor ShapeMagnitude

Possible improvements  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. O’Dowd et al. Keene et al. Quinn & Bates et al. Meskhidze & Peters et al. μm25μm1 80  r μm250μm  r...),,(f )( f bar r ,,()( baUWU W  6 Dec, 20114Whitecaps and sea spray, Anguelova et al., NRL (de Leeuw et al., 2011) Ernie Lewis poster Sofiev et al., 2011

Objective  Measure W globally  Compile database  Model the high variability of whitecap fraction U – wind speed (U 10 or u * )  T – atmospheric stability (= T air – T sea ) X – wind fetch d – wind duration U cur – water currents T s – sea surface temperature S – salinity C k – concentration, type (k) of surface active materials  CSTUdXTUW scur,,,,,,,    UW 6 Dec, 20115Whitecaps and sea spray, Anguelova et al., NRL

Whitecaps signature High Reflectivity High Emissivity Reflectivity Emissivity Vis IRmW 6 Dec, 20116Whitecaps and sea spray, Anguelova et al., NRL

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   sB fr T e T eWeWe   1 6 Dec, 20117Whitecaps and sea spray, Anguelova et al., NRL

Models  Rough sea surface model  2-scale  Wave spectrum  Durden/Vesecky/Yueh  Tuned for roughness only  Using WindSat code (v )  Foam emissivity model  RT model  Layer with vertically non-uniform properties  Distribution of thicknesses © P.R.Hemington z = 0 z = -d Air, ε 0 =1 Water, ε Foam, ε (z) Courtesy of Prof. Cilliers   fr eWeWe  1 6 Dec, 20118Whitecaps and sea spray, Anguelova et al., NRL Anguelova and Webster, 2006 Anguelova et al., 2006

Data  Independent sources  T B from WindSat  V, L from SSM/I or TMI  U 10 and  from QuikSCAT or GDAS  T s from GDAS  S = 34 psu  Trade-off:  Sampling issues  Use long-term data Sample count 6 Dec, 20119Whitecaps and sea spray, Anguelova et al., NRL

Estimates of W  Improvements over the feasibility study (Anguelova and Webster, 2006) :  More physical models  Independence of the variables 6 Dec, Whitecaps and sea spray, Anguelova et al., NRL

Compare to photographic data 6 Dec, Whitecaps and sea spray, Anguelova et al., NRL

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 o and COARE CO2 parameterization  AOD from AERONET o and AOD from microphysical aerosol model  Uncertainty characterization  Currently uncertainty minimization  Evaluate the remaining using global geophysical model 6 Dec, Whitecaps and sea spray, Anguelova et al., NRL

Whitecaps data base  All available orbits for  Resolution 50×70 km 2  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 6 Dec, Whitecaps and sea spray, Anguelova et al., NRL

Geographic characteristics of W March,  x 0.5  Wind speed formula Satellite, 10.7 GHz, H pol. 6 Dec, Whitecaps and sea spray, Anguelova et al., NRL

Geographic characteristics of W March,  x 0.5  Wind speed formula 18.7 Satellite, 18.7 GHz, H pol. 6 Dec, Whitecaps and sea spray, Anguelova et al., NRL

Develop parameterization(s)  Relative importance of the variables  Correlation analysis  CSTUdXTUW scur,,,,,,,    UW 6 Dec, Whitecaps and sea spray, Anguelova et al., NRL Fetch SST Stability Wave height Wave period Wind

New sea spray source function  Include wave-field characteristics and one more factor  Improve/choose size distribution  Include organics    ss s THUW HUW,,, 6 Dec, Whitecaps and sea spray, Anguelova et al., NRL )f() rU   dr bardF,...,, Size distributionScaling factor ShapeMagnitude

Sea-salt flux  Solar irradiance at TOA (W/m 2 ) : GCM – ERBE  NO aerosols;  Max difference over the oceans. 2         10 5 Number flux, dF (s -1 m -2 ) Annual sea-salt flux (1998) 6 Dec, Whitecaps and sea spray, Anguelova et al., NRL Haywood et al., Science, 1999 Anguelova and Webster, 2006

Sea foam definition  Oceanographic definition  Whitecaps on the surface  Bubble plumes below  Passive remote sensing  Radiometers detect only the surface foam layers  Skin depth  At microwave frequencies  a few mm to a few cm 6 Dec, Whitecaps and sea spray, Anguelova et al., NRL

Photographic measurements  High uncertainty: up to 30% or more  Intensity threshold  A and B stages under oblique angle  Patchy coverage  Open ocean  Southern ocean! 6 Dec, 2011Whitecaps and sea spray, Anguelova et al., NRL20 Stramska and Petelski, 2003

Improvements and restrictions 6 Dec, Whitecaps and sea spray, Anguelova et al., NRL (de Leeuw et al., 2011) Whitecap fraction, W (%)

Modeling whitecap fraction 6 Dec, Whitecaps and sea spray, Anguelova et al., NRL