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

MotivationSea 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

Ph

oto

cou

rtesy

of

C. Fa

irall

6 Dec, 2011 2Whitecaps and sea spray, Anguelova et al.,

NRL

Sea spray source functionRate of production of sea spray per unit area per

increment of droplet radius, r (s-1 m-2 m-1).

)f()f( rU

dr

bardF ,...,,

From photographic measurements

(Monahan and O’Muircheartaigh, 1980)

From measurements using various methods

41.310

610 108.3)()(f UUWU

8010

80

log

f)(f

rd

rdr

6 Dec, 2011 3Whitecaps and sea spray, Anguelova et al.,

NRL

Size distributionScaling factorShapeMagnitude

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.de Leeuw et al.O’Dowd et al.O’Dowd et al.Keene et al.Keene et al.Quinn & Bates et al. Quinn & Bates et al. Meskhidze & Peters et al.Meskhidze & Peters et al.

μm25μm1 80 r μm250μm1.0 80 r

...),,(f)(f barr

...),,()( baUWUW

6 Dec, 2011 4Whitecaps and sea spray, Anguelova et al.,

NRL

(de Leeuw et al., 2011)

Ernie Lewis posterErnie Lewis posterSofiev et al., 2011Sofiev et al., 2011

ObjectiveMeasure W globallyCompile databaseModel the high variability of whitecap

fraction

U – wind speed (U10 or u*)T – atmospheric stability (= Tair – Tsea)X – wind fetch d – wind durationUcur – water currentsTs – sea surface temperatureS – salinityCk – concentration, type (k) of surface active materials

CSTUdXTUW scur ,,,,,,, UW

6 Dec, 2011 5Whitecaps and sea spray, Anguelova et al.,

NRL

Whitecaps signatureHigh

ReflectivityHigh

Emissivity

Reflectivity

Emissivity

VisVis IRIR mWmW

6 Dec, 2011 6Whitecaps 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

TeT

eWeWe

1

6 Dec, 2011 7Whitecaps and sea spray, Anguelova et al.,

NRL

ModelsRough 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

ww

w.p

base

.com

/pete

hem

/

© P.R.Hemington

z = 0

z = -d

Air, ε0=1

Water, ε

Foam, ε (z)

Courtesy of Prof. Cilliers

fr eWeWe 1

6 Dec, 2011 8Whitecaps and sea spray, Anguelova et al.,

NRL

Anguelova and Webster, 2006Anguelova et al., 2006

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 9Whitecaps 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, 2011 10Whitecaps and sea spray, Anguelova et al.,

NRL

Compare to photographic data

6 Dec, 2011 11Whitecaps 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 cruiseso and COARE CO2 parameterization

AOD from AERONETo and AOD from microphysical aerosol model

Uncertainty characterization Currently uncertainty minimization Evaluate the remaining using global geophysical model

6 Dec, 2011 12Whitecaps and sea spray, Anguelova et al.,

NRL

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 13Whitecaps and sea spray, Anguelova et al.,

NRL

Geographic characteristics of W

310UW

March, 2007 0.5 x 0.5

Wind speed formula

Satellite, 10.7 GHz, H pol.

6 Dec, 2011 14Whitecaps and sea spray, Anguelova et al.,

NRL

Geographic characteristics of W

March, 2007 0.5 x 0.5

Wind speed formula

Satellite, 18.718.7 GHz, H pol.

6 Dec, 2011 15Whitecaps and sea spray, Anguelova et al.,

NRL

Develop parameterization(s)

Relative importance of the variablesCorrelation analysis

CSTUdXTUW scur ,,,,,,, UW

6 Dec, 2011 16Whitecaps and sea spray, Anguelova et al.,

NRL

FetchFetch

SSTSST

StabilityStability

Wave heightWave height

Wave periodWave period

WindWind

New sea spray source function

Include wave-field characteristics and one more factor

Improve/choose size distributionInclude organics

ss

s

THUW

HUW

,,

,

6 Dec, 2011 17Whitecaps and sea spray, Anguelova et al.,

NRL

)f()f( rU

dr

bardF ,...,,

Size distributionScaling factorShapeMagnitude

Sea-salt flux

Solar irradiance at TOA (W/m2): GCM – ERBE

NO aerosols; Max difference over the

oceans.

22101055 4 4101055 6 6101055 8 8101055

Number flux, Number flux, dFdF (s (s-1-1 m m-2-2 ) )

Annual sea-salt flux (1998)

6 Dec, 2011 18Whitecaps 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, 2011 19Whitecaps and sea spray, Anguelova et al.,

NRL

Photographic measurements

High uncertainty: up to 30% or moreIntensity thresholdA and B stages under oblique angle

Patchy coverageOpen ocean Southern ocean!

6 Dec, 2011Whitecaps and sea spray, Anguelova et al.,

NRL20

Stramska and Petelski, 2003

Improvements and restrictions

),(

),(

)(

10

10

10

sTUW

TUW

UW

6 Dec, 2011 21Whitecaps and sea spray, Anguelova et al.,

NRL

(de Leeuw et al., 2011)

Modeling whitecap fraction

6 Dec, 2011 22Whitecaps and sea spray, Anguelova et al.,

NRL