Sea salt aerosols: Their generation and role in the climate system
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Transcript of Sea salt aerosols: Their generation and role in the climate system
Sea salt aerosols: Their generation
and role in the climate system
Ph. D. Dissertation Proposal
Magdalena D. Anguelova
November 12, 1999College of Marine Studies
University of Delaware
Outline
What? Problem statement
How? ImplementationImplementation
Why? ImplicationsImplications
Problem statement
Modify the currently available sea-salt generation function.
Evaluate the effect of sea-salt aerosols on the climate system.
The Role of the Aerosols
In climate:
In atmospheric chemistry:
Scatter sunlight; Facilitate cloud
droplet formation;
Provide site for chemical reactions.
““...... However, it generates too much big sea-salt particles However, it generates too much big sea-salt particles at high wind speeds compared to observations and is at high wind speeds compared to observations and is therefore neglected in the simulation.”therefore neglected in the simulation.”
Aerosols in Climate Models
Improves model predictions; Canadian Climate Model
(Gong, Barrie, Blanchet, 1997) Use the first sea-salt generation function
(Monahan et al., 1986)
Sea Spray Formation
Direct; Indirect.
Andreas et al., 1995
Sea Spray Sizes
r, m5001001010.1
Film drops: 0.5 to 5 m
Jet drops: 3 to 50 m
Spume drops: 20 to > 500 m
Andreas, 1998
Sizes Relevant to Aerosol Forcing
Long residence time.
Gravitational settling.
Heat exchangeAerosol forcing
r, m5001001010.1
Modeling Sea Spray
dF/dr = dF0 /dr + dF1 /drMonahan et al., 1986
r, m5001001010.1 0.8
Modeling the Indirect Mechanism
d F0 /d r = 1.373 U103.41 r -3(1 + 0.057r1.05) 101.19e -B2
B = (0.38 - log r) / 0.65Monahan et al., 1986
d F0 /d r = f (U10 , r)
Whitecap coverage W
Modeling the Direct Mechanism
d F1 /d r = C1 (U10) r -1 10 m r 37.5 m
d F1 /d r = C2 (U10) r -2.8 37.5 m r 100 m
Andreas, 1998
d F1 /d r = f (U10 , r)
Coefficients Ci
The Goal
d F0 /d r
d F /d r = f (U10 , r)
f (U10 , T, Ts , S, f , d , C, r)
??W (U10 , T, Ts , S, f , d , C)
d F1 /d r
Ci (U10 , T, Ts , S, f , d , C) Method Method
Ts
The Concept e - es ef - es
W =
eTs =
CalculatedCalculatedObservedObserved
TB= es (1-W )Ts + W ef Ts
BA
The Procedure
Data Compute W Preparation
Brightness temperature;
Wind mask; Cloud mask; Rain mask; Available Ts;
Calculate e; Calculate es;
Calculate ef ; Calculate W.
e
es
es Salinity;
Sea surface temperature;
Brightness Temperature
TB (h), K
March 27, 1998 Ascending pass SSM/I19 GHz
Grid: 0.5o 0.5o
DataData
Sea Surface Temperature
Ts , oC
AVHRRAVHRR
DataData
Wind Mask
U10 , m s-1
U10 > 10 m s-1
PreparationPreparation
Cloud Mask
L , mg cm-2
L < 5 mg cm-2
PreparationPreparation
Rain Mask
TB (h), K
TB (37v) - TB (37h) > 50 and
TB (19h) < T1
130 K
165 K
165 K
175 K
PreparationPreparation
All Masks on TB
TB (h), K
e
PreparationPreparation
All Masks on SST
Ts , oC
es
PreparationPreparation
Available TB
TB (h), K
PreparationPreparation
Emissivity of Sea Water
e (h)0.29 to 0.45
Results
Specular Emissivity
es (h)0.26 to 0.28
e
Results
Emissivity of Foam
ef (h)0.91 to 0.94
ees
Results
Whitecap Coverage
W (h)
Results
Comparison
W (h)
e - es ef - es
W =
W = 3.8410-6 U10
Conventional Method
Proposed Method
4% - 30%4% - 30%
1% - 19%1% - 19%
Questions
The Boasting Traveller, Aesop
"Deeds speak louder than
words"