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"