Magdalena D. Anguelova, Ferris Webster, Peter Gaiser 12 May, 2004 Effects of Environmental Variables in Sea Spray Generation Function via Whitecap Coverage

Magdalena D. Anguelova, Ferris

Webster, Peter Gaiser

12 May, 2004

Effects of Environmental Effects of Environmental Variables in Sea Spray Variables in Sea Spray

Generation Function via Generation Function via Whitecap Coverage Whitecap Coverage

Effects of Environmental Effects of Environmental Variables in Sea Spray Variables in Sea Spray

Generation Function via Generation Function via Whitecap Coverage Whitecap Coverage

Remote Sensing Physics Branch

Naval Research LaboratoryWashington, DC

Workshop: Toward a Universal Sea Spray Source Function

Skipton, UK, 11-13 May, 2004

Sea Spray Workshop, May 2004

OutlineOutlineOutlineOutline

Motivation and objectives; Whitecap coverage estimation; Generation of sea spray; Summary and future work.


Sea Spray and ClimateSea Spray and ClimateSea Spray and ClimateSea Spray and Climate Heat exchange; Gas exchange; Sea-salt aerosols:

Direct effect – cooling; Indirect effect:

Dominate the activation of CCN; Compete with SO4

2- aerosols;

Halogen chemistry: Reactive Cl and Br; Tropospheric O3; Sink of S.


Rate of production of sea spray per unit area per increment of droplet radius, r (s-1 m-2 m-

1).

Sea spray generation Sea spray generation functionfunctionSea spray generation Sea spray generation functionfunction

dr

dF

dr

dr

f)f( Explicit forms for 4 size regions

covering 1.6 to 500 m range. Andreas (2001)

41.310

61010 108.3)()f( UUWU (Monahan and

O’Muircheartaigh, 1980)

)f()f( 10 rU


Sea-salt concentrationsSea-salt concentrationsSea-salt concentrationsSea-salt concentrations High variability of C(U10):

r2 = 0.14 to 0.91

Exton et al., 1985Hoppel et al.,1989Gong et al., 1997Quinn & Coffman, 1999

Due to: Either processes in the atmosphere:

Transport: Mixing; Advection; Deposition;

Chemistry: Particle-to-particle conversions; In cloud processing;

Or…


Source function variabilitySource function variabilitySource function variabilitySource function variability

)f()()f()f( 1010 rUWrUdr

dF


Various whitecap coverage parametrizations

0.0001

0.001

0.01

0.1

1

10

100

0 5 10 15 20 25 30 35 40

Wind speed, U 10 (m s-1)

Wh

itec

ap c

ov

erag

e,

W(%

)

Monahan '71Wilheit '79M&O'M '80 RBFM&O'M '80 OLSBondur&Sharkov'82 ABondur&Sharkov'82 BPandey&Kakar 82Monahan et al. '83Spillane et al'86 coldSpillane et al'86 moder.Spillane et al'86 warmM&O'M 86 dT=0 (neutral)Bortk'87, A+B, coldBortk'87, A+B, moderBortk'87, A+B, warmWu '88Mon&Woolf'89, AMonhan'93 visc., AMonhan'93 visc., BAsher&Wann'98, AHanson&Phillips'99, no <<Hanson&Phillips'99, all measAsher et al.'02Reising et al. '02, AWentz '02 HpolWentz '02 VpolStram&Petel'03 totStram&Petel'03 dev. Stram&Petel'03 undev.Villarino et al '03, stableVillarino et al '03, unst.

Source function variabilitySource function variabilitySource function variabilitySource function variability

)f()()f()f( 1010 rUWrUdr

dF


Additional factors Additional factors Additional factors Additional factors Introduce:

Meteorological conditions; Environmental factors;

)f()( 10 rUWdr

dF

W(U10, T, Ts , S, f , d , C )

(Monahan and O’Muircheartaigh, 1986)

) , C ), T, Ts , S , f , d , C ), Ts , S , f , d Need of data base; Existing measurements.


-180 -120 -60 0 60 120 180

90

60

30

0

-30

-60

-90

Open ocean?Open ocean?Open ocean?Open ocean?


Range of conditionsRange of conditionsRange of conditionsRange of conditions

307 points477 points

),(

),(

)(

10

10

10

sTUW

TUW

UW

CdfSTs ,,,, more


Subjective analysisSubjective analysisSubjective analysisSubjective analysis Intensity threshold; A and B stages in oblique view High uncertainty:

Up to 30%; Higher

Stramska and Petelski, 2003


Alternative approachAlternative approachAlternative approachAlternative approach Open ocean conditions; Range of conditions; Subjective analysis.





Whitecaps signatureWhitecaps signatureWhitecaps signatureWhitecaps signature

High Reflectivit

y

High Emissivity

Reflectivity

Emissivity

Vis IR mWUV

TB


Ocean emissivity is compositee

Method conceptMethod conceptMethod conceptMethod concepte as W Emissivity of foam-free

ocean is low.

Emissivity of foam-covered ocean is high.

e – es – er ef – es – er

W == (es + er)(1-W ) + W ef


Calculate emissivitiesCalculate emissivitiesCalculate emissivitiesCalculate emissivities Composite emissivity e:

Specular emissivity es:

Foam emissivity ef :

Roughness correction er:

Radiative transfer equation

Fresnel formula, Debye equation

Fresnel formula, empirical relation

Empirical relation

TB, V, L

Ts, S

Ts, S

U10, Ts

SSM/I

AVHRRNOAA

SSM/IAVHRR


-180 -120 -60 0 60 120 180

90

60

30

0

-30

-60

-90

Longitude

Lat

itu

de

0.00 0.02 0.04 0.06 0.08 0.10

Whitecap coverage, W

Whitecap coverageWhitecap coverageWhitecap coverageWhitecap coverage27 March

1998


Accuracy Accuracy Accuracy Accuracy

0 10 20 30 40 50 60 70 80 90 1000

40

80

120

160

200

240

280

320

Relative error of W

Cou

nt

Relative error, W/W (%)

Cou

nt


Validation with Validation with previousprevious datadataValidation with Validation with previousprevious datadata


Magnitude; Trend:

Suppression at high winds;

Enhancement at moderate winds.

Variability!

Validation with Validation with previousprevious datadataValidation with Validation with previousprevious datadata


Spatial distributionSpatial distributionSpatial distributionSpatial distribution Same magnitude; Different spatial

features: More uniform; 3% instead of 1%.

-180 -120 -60 0 60 120 180

90

60

30

0

-30

-60

-90

Longitude

Lat

itu

de

0.00 0.02 0.04 0.06 0.08 0.10


March 1998 W U10

3

-180 -120 -60 0 60 120 180

90

60

30

0

-30

-60

-90

Longitude

Lat

itu

de

0.00 0.02 0.04 0.06 0.08 0.10



-180 -120 -60 0 60 120 180

90

60

30

0

-30

-60

-90

Longitude

Lat

itu

de

0.00 0.02 0.04 0.06 0.08 0.10


Effects of additional Effects of additional factorsfactorsEffects of additional Effects of additional factorsfactors

-180 -120 -60 0 60 120 180

90

60

30

0

-30

-60

-90

-3 0 3 6 9 12 15 18 21 24 27 30 33

Wind speed, U10 (m s-1)

Sea surface temperature, Ts (oC)

Wind fetch and duration; Surface-active material.

March 1998





Modified source functionModified source functionModified source functionModified source function

Use new global estimates for f(U10); Chose size dependence f(r).

)f()f(),(

1010 rU

dr

UrdF

W(U10)

(Monahan and O’Muircheartaigh, 1986)

W(U10, T, Ts , S, f , d , C )


Modified source functionModified source functionModified source functionModified source function

1010

0

f),,,,,,(

dr

dCdfSTTUW

dr

dFs 206.1 0 r

2010

0

f),,,,,,(

dr

dCdfSTTUW

dr

dFs 6.14.0 0 r

3010

0

f),,,,,,(

dr

dCdfSTTUW

dr

dFs 4.01.0 0 r

Assimilating new method estimates

Andreas, 2002

Monahan et al., 1986

Future work

m

m

m


Radius at formation, r0 (m)

0.1 1 10 100

Num

ber

flux

, dF

/dr 0 (

s-1 m

-2

m-1

)

102

103

104

105

106

New methodWind formula

Radius, r80 (m)

1 10

Num

ber

conc

entr

atio

n, dN

/dr 80

(m

l-1

m-1

)

10-6

10-5

10-4

10-3

10-2

10-1

100

101

102

103

5 m/s (Smith et al., 1993)30 m/s (Smith et al., 1993)11.2 m/s This study

Function performanceFunction performance Current function (Andreas, 2002)

Measurements (Smith et al., 1993)


Sea-salt aerosol loadingSea-salt aerosol loadingSea-salt aerosol loadingSea-salt aerosol loading

Magnitude; Weak wind dependence;

5.0 10.0 15.0 20.0 25.0 30.0

0

50

100

150

200

250

300

Cou

nt

Ts in places with

U10 = 10 m s-1

Sea surface temperature, Ts oC 5.0 10.0 15.0 20.0 25.0 30.0

0

50

100

150

Cou

nt

Ts in places with

U10 = 15 m s-1


Sea spray spatial Sea spray spatial distributiondistribution

-180 -120 -60 0 60 120 180

90

60

30

0

-30

-60

-90

Longitude

Lat

itud

e

1.0e+005 4.0e+005 7.0e+005 1.0e+0061105 4105 7105 1106

Number flux, dF/dr0 (# m-1 m-2 s-1)

Haywood et al., 1999Model - Experiment





SummarySummarySummarySummary Variability of sea spray source

function due to environmental factors;

Whitecap coverage can account for them;

Alternative approach for global whitecap coverage;

Modification of sea spray source function.


Future workFuture workFuture workFuture work Improvements in whitecap coverage

estimates: es – all available models considered and compared; er – 2-scale model; ef – full RT model for a foam layer with void fraction

changing with depth; e – decoupling of satellite measurements;

Parameterizations: Initial steps for W(U10, Ts) encouraging; Identify more suitable methods and functions fitting

highly variable data; Revise W(U10, Ts); Investigate correlations W(S), W(f), W(d), W©.


Documents

Magdalena D. Anguelova, Ferris Webster, Peter Gaiser 12 May, 2004 Effects of Environmental Variables in Sea Spray Generation Function via Whitecap Coverage