magdalena d. anguelova, ferris webster, peter gaiser 12 may, 2004 effects of environmental variables...
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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 Workshop, May 2004
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.
Sea Spray Workshop, May 2004
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 Spray Workshop, May 2004
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…
Sea Spray Workshop, May 2004
Source function variabilitySource function variabilitySource function variabilitySource function variability
)f()()f()f( 1010 rUWrUdr
dF
Sea Spray Workshop, May 2004
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
Sea Spray Workshop, May 2004
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.
Sea Spray Workshop, May 2004
-180 -120 -60 0 60 120 180
90
60
30
0
-30
-60
-90
Open ocean?Open ocean?Open ocean?Open ocean?
Sea Spray Workshop, May 2004
Range of conditionsRange of conditionsRange of conditionsRange of conditions
307 points477 points
),(
),(
)(
10
10
10
sTUW
TUW
UW
CdfSTs ,,,, more
Sea Spray Workshop, May 2004
Subjective analysisSubjective analysisSubjective analysisSubjective analysis Intensity threshold; A and B stages in oblique view High uncertainty:
Up to 30%; Higher
Stramska and Petelski, 2003
Sea Spray Workshop, May 2004
Alternative approachAlternative approachAlternative approachAlternative approach Open ocean conditions; Range of conditions; Subjective analysis.
Sea Spray Workshop, May 2004
OutlineOutlineOutlineOutline
Motivation and objectives; Whitecap coverage estimation; Generation of sea spray; Summary and future work.
Sea Spray Workshop, May 2004
Whitecaps signatureWhitecaps signatureWhitecaps signatureWhitecaps signature
High Reflectivit
y
High Emissivity
Reflectivity
Emissivity
Vis IR mWUV
TB
Sea Spray Workshop, May 2004
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
Sea Spray Workshop, May 2004
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
Sea Spray Workshop, May 2004
-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
Sea Spray Workshop, May 2004
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
Sea Spray Workshop, May 2004
Validation with Validation with previousprevious datadataValidation with Validation with previousprevious datadata
Sea Spray Workshop, May 2004
Magnitude; Trend:
Suppression at high winds;
Enhancement at moderate winds.
Variability!
Validation with Validation with previousprevious datadataValidation with Validation with previousprevious datadata
Sea Spray Workshop, May 2004
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
Whitecap coverage, W
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
Whitecap coverage, W
Sea Spray Workshop, May 2004
-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
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
Sea Spray Workshop, May 2004
OutlineOutlineOutlineOutline
Motivation and objectives; Whitecap coverage estimation; Generation of sea spray; Summary and future work.
Sea Spray Workshop, May 2004
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 )
Sea Spray Workshop, May 2004
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
Sea Spray Workshop, May 2004
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 Spray Workshop, May 2004
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 Workshop, May 2004
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
Sea Spray Workshop, May 2004
OutlineOutlineOutlineOutline
Motivation and objectives; Whitecap coverage estimation; Generation of sea spray; Summary and future work.
Sea Spray Workshop, May 2004
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.
Sea Spray Workshop, May 2004
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©.
Sea Spray Workshop, May 2004