whitecaps, sea-salt aerosols, and climate magdalena d. anguelova physical oceanography dissertation...
Post on 01-Apr-2015
216 Views
Preview:
TRANSCRIPT
Whitecaps, sea-salt aerosols, and climate
Magdalena D. Anguelova
Physical Oceanography
Dissertation Symposium
College of Marine Studies, University of Delaware
June 17-21, 2002Breckenridge, Colorado
What?
Outline
How?
Why?
Work
Background
Results
Aerosol effects
IPCC, 2001
Assessment: Effect of anthropogenic aerosols = Effect of all aerosols – Effect of natural aerosols
Aerosol radiative forcing Defined as…
natural
Background atmosphere Natural aerosols; Baseline of an unperturbed
atmosphere.
Background baseline
Sea-salt aerosols are the dominant aerosol species in background
atmosphere.
Sea-salt aerosols
Natural aerosols; Baseline of an unperturbed
atmosphere.
Formation of sea-salt aerosols
Sea spray;
Droplet sizes:• 0.5-500 m;• < 20 m;
Sea-salt aerosols:• Phase state;• Sizes: 0.025 to 20 m.
Sea-salt aerosol effects must be accounted for in climate models.
Motivation
Modeling sea-salt aerosols
Generation; Transport; Diffusion and convection; Chemical and physical
transformations:• in clear air;• in clouds;• below clouds;
Wet and dry deposition.
Generation
Rate of production of sea spray per unit area per increment of droplet radius, r (s-1 m-2 m-
1).
Sea spray generation function
dr
dF
dr
dfrf )( Explicit forms for 4 size regions
covering 1.6 to 500 m range. Andreas (2001)
41.310
61010 108.3)()( UUWUf (Monahan and
O’Muircheartaigh, 1980)
Best)()( 10 rfUf
Improved generation function?
)()( 10 rfUfdr
dF
r0 1.6 mMeasurements
0.1
W(U10, T, Ts , S, f , d , C )
(Monahan and O’Muircheartaigh, 1986)
) , C ), T, Ts , S , f , d , C ), Ts , S , f , d
Whitecap coverage
Need for a database
W (U10 , T, Ts , S, f , d , C )
-180 -120 -60 0 60 120 180
90
60
30
0
-30
-60
-90
1
2
3
45 6
7
9
1011
1213
14
1516
Need of a database
W (U10 , T, Ts , S, f , d , C )
1
2
3
45 6
7
9
1011
1213
14
1516
307 points477 points
New meth
od
Outline
Work
Background
Results
Ocean emissivity is compositee
Method concept
e 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
The task: calculate 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
Valid estimation of W
rsf
rs
eee
eeeW
W < 0
e < es + er
Brightness Temperature, TB (K)
100 120 140 160 180
Whi
teca
p co
vera
ge, W
(%
)
0
10
20
30
40
50
L = 0 mmS = 35 psuTs = 20 oCQ = 2 %U10 = 9 m s-1
V mm
8
20
35
50
Brightness Temperature, TB (K)
100 120 140 160 180
Whi
teca
p co
vera
ge, W
(%
)
0
10
20
30
40
50
L = 0 mmS = 35 psuTs = 20 oCQ = 2 %U10 = 9 m s-1
V mm
8
20
35
50
Brightness Temperature, TB (K)
100 120 140 160 180
Whi
teca
p co
vera
ge, W
(%
)
0
10
20
30
40
50
L = 0 mmS = 35 psuTs = 20 oCQ = 2 %U10 = 9 m s-1
V mm
8
20
35
50
Brightness Temperature, TB (K)
100 120 140 160 180
Whi
teca
p co
vera
ge, W
(%
)
0
10
20
30
40
50
L = 0 mmS = 35 psuTs = 20 oCQ = 2 %U10 = 9 m s-1
V mm
8
20
35
50
2 – 10 %
Error of W
Method 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
-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 coverage27 March
1998
Validation with in situ data
Validation with in situ data
Magnitude; Trend:
• Suppression at high winds;
• Enhancement at moderate winds.
Variability!
Outline
Work
Background
Results
Database
Use:• Investigate spatial and temporal
characteristics of global whitecap coverage;
• Evaluate whitecap contribution to climate processes.
• Parameterize effects of additional factors on whitecaps;
Content:• Daily and monthly estimates of W and W
for the entire 1998;• Collocated measurements of U10, Ts, S;
Spatial 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
-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 factors
-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
Ocean surface albedo Natural
climate agent; Average:
0.11 W m-2;
Anthropogenic agents:
•Stratospheric ozone (0.18 W m-2)
•Biomass burning (0.21 W m-2)
•Land use (0.22 W m-2)
-180 -120 -60 0 60 120 180
90
60
30
0
-30
-60
-90
Longitude
Lat
itud
e
0.00 0.04 0.08 0.12 0.16 0.20
Radiative flux changes, F (W m‑2)
CO2 transfer velocity
5 – 150 cm h-1; Average:
56.8 cm h-1; Tropics are
source of CO2; Southern
Ocean is sink of CO2.
CO2 transfer velocity, kCO2 (cm h‑2)
-180 -120 -60 0 60 120 180
90
60
30
0
-30
-60
-90
Longitude
Lat
itud
e
0 30 60 90 120 150
Flux = kCO2 C
Improved generation function?
)()(),(
1010 rfUf
dr
UrdF
r0 1.6 mMeasurements
0.1
W(U10)
(Monahan and O’Muircheartaigh, 1986)
W(U10, T, Ts , S, f , d , C )
Modified generation function
1010
0
),,,,,,(
dr
dfCdfSTTUW
dr
dFs 206.1 0 r
2010
0
),,,,,,(
dr
dfCdfSTTUW
dr
dFs 6.14.0 0 r
3010
0
),,,,,,(
dr
dfCdfSTTUW
dr
dFs 4.01.0 0 r
Assimilating new method estimates
Andreas, 2001
Monahan et al., 1986
Future work
m
m
m
Sea-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
Haywood et al., 1999Model - Experiment
Spatial distribution of sea-salt
-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)
Direct effect: 15 W m-2
Conclusions
Whitecap coverage estimation
Whitecap coverage database
Generation of sea-salt aerosols
top related