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 Motivation Whitecaps Gas exchange Ocean albedo & roughness Geophysical retrievals Dominate the activation of CCN Sea spray aerosols Direct effect – cooling Indirect effect Halogen chemistry Reactive Cl and Br Tropospheric O3 Sink of S Surface wind Ocean color Salinity Sea spray droplets Heat exchange Tropical storm intensification 6 Dec, 2011 Whitecaps and sea spray, Anguelova et al., NRL Photo courtesy of C. Fairall Compete with SO42- aerosols 2 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). dF (r , a, b,... ) = f(U ) f( r ) dr Scaling factor Size distribution Magnitude Shape -6 3.41 = f (U ) W (U10 ) 3.8 10 U10 From photographic measurements (Monahan and O’Muircheartaigh, 1980) f (r80 ) d f (r ) d log10 r80 6 Dec, 2011 From measurements using various methods Whitecaps and sea spray, Anguelova et al., NRL 3 Possible improvements For the size distribution f(r) Extend the size range, large and small ends 1 μm < r80 < 25 μm de Leeuw et al. O’Dowd et al. Keene et al. Quinn & Bates et al. Meskhidze & Peters et al. 0.1 μm < r80 < 250 μm Recognize and include the effect of organics Introduce ambient factors f (r) f ( r , a , b ...) (de Leeuw et al., 2011) Ernie Lewis poster Sofiev et al., 2011 For the scaling factor f(U) Less uncertainty in measuring W Introduce ambient factors W (U ) W (U , a , b ...) Remote sensing: method, results, implications 6 Dec, 2011 Whitecaps and sea spray, Anguelova et al., NRL 4 Objective Measure W globally Compile database Model the high variability of whitecap fraction W (U ) W (U , T , X , d ,U cur , Ts , S , C) 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 6 Dec, 2011 Whitecaps and sea spray, Anguelova et al., NRL 5 Whitecaps signature High Reflectivity Vis 6 Dec, 2011 Reflectivity Emissivity High Emissivity IR Whitecaps and sea spray, Anguelova et al., NRL mW 6 Remote sensing of sea foam Microwave region Advantages e = (1 - W ) er + W e f TB = e Ts 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 6 Dec, 2011 Whitecaps and sea spray, Anguelova et al., NRL 7 Rough sea surface model 2-scale Wave spectrum e = (1 - W ) er + W e f Anguelova and Webster, 2006 Anguelova et al., 2006 Durden/Vesecky/Yueh Tuned for roughness only Using WindSat code (v. 1.9.6) © P.R.Hemington z=0 Foam emissivity model RT model Layer with vertically non-uniform properties Distribution of thicknesses Air, ε0=1 Foam, ε (z) Courtesy of Prof. Cilliers 6 Dec, 2011 www.pbase.com/petehem/ Models Whitecaps and sea spray, Anguelova et al., NRL Water, ε z = -d 8 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 6 Dec, 2011 Whitecaps and sea spray, Anguelova et al., NRL 9 Estimates of W Improvements over the feasibility study (Anguelova and Webster, 2006): More physical models Independence of the variables 6 Dec, 2011 Whitecaps and sea spray, Anguelova et al., NRL 10 Compare to photographic data 6 Dec, 2011 Whitecaps and sea spray, Anguelova et al., NRL 11 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, 2011 Whitecaps and sea spray, Anguelova et al., NRL 12 Whitecaps data base All available orbits for Resolution 50×70 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 6 Dec, 2011 Whitecaps and sea spray, Anguelova et al., NRL 13 Geographic characteristics of W March, 2007 0.5 x 0.5 Wind speed formula W U103 Satellite, 10.7 GHz, H pol. 6 Dec, 2011 Whitecaps and sea spray, Anguelova et al., NRL 14 Geographic characteristics of W March, 2007 0.5 x 0.5 Wind speed formula Satellite, 18.7 GHz, H pol. 6 Dec, 2011 Whitecaps and sea spray, Anguelova et al., NRL 15 Develop parameterization(s) W (U ) W (U , T , X , d ,U cur , Ts , S , C) Relative importance of the variables Correlation analysis Wind Fetch SST Stability Wave height Wave period 6 Dec, 2011 Whitecaps and sea spray, Anguelova et al., NRL 16 New sea spray source function dF (r , a, b,... ) = f(U ) f( r ) dr Scaling factor Size distribution Magnitude Shape Include wave-field characteristics and one more factor W (U, H ) s W (U , H s , Ts ) Improve/choose size distribution Include organics 6 Dec, 2011 Whitecaps and sea spray, Anguelova et al., NRL 17 Sea-salt flux Annual sea-salt flux (1998) Haywood et al., Science, 1999 Anguelova and Webster, 2006 2105 Solar irradiance at TOA (W/m2) : 4105 6105 8105 Number flux, dF (s-1 m-2 ) GCM – ERBE NO aerosols; Max difference over the oceans. 6 Dec, 2011 Whitecaps and sea spray, Anguelova et al., NRL 18 Sea foam definition Oceanographic definition Passive remote sensing Whitecaps on the surface Radiometers detect only the Bubble plumes below surface foam layers Skin depth At microwave frequencies a few mm to a few cm 6 Dec, 2011 Whitecaps and sea spray, Anguelova et al., NRL 19 Photographic measurements High uncertainty: up to 30% or more Intensity threshold A and B stages under oblique angle Stramska and Petelski, 2003 Patchy coverage Open ocean Southern ocean! 6 Dec, 2011 Whitecaps and sea spray, Anguelova et al., NRL 20 Improvements and restrictions (de Leeuw et al., 2011) W (U10 ) W (U10 , T ) Whitecap fraction, W (%) W (U10 , Ts ) 6 Dec, 2011 Whitecaps and sea spray, Anguelova et al., NRL 21 Modeling whitecap fraction 6 Dec, 2011 Whitecaps and sea spray, Anguelova et al., NRL 22