presented at ams meeting, long beach, ca, 2003 aerosol phase function and size distributions from...
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Presented At AMS Meeting, Long Beach, CA, 2003
Aerosol Phase Function And Size Distributions From Polar Nephelometer
Measurements During The SEAS Experiment
By John Porter, Barry Lienert and Shiv Sharma
Hawaii Institute of Geophysics and PlanetologyUniversity of Hawaii
Aerosol Phase Function Describes The Angular Distribution of Light Scattered By Aerosols.
Three Parameters Needed For Optical Calculations - Phase Functions - Absorption Coefficient - Scattering Coefficient
How To Calculate the Phase Function ?For Simple Aerosols Mie Theory Works WellFor Complex Aerosol Other Approaches Are Needed
(T-Matrix, Finite Difference, Discrete Dipole …)
But Often The Aerosol Composition, Shape And Index Of Refraction Are Not Known So MeasurementsOf The Aerosol Phase Function Are Useful
Particle Phase Function Are Fairly Complex But In General:
Aerosol Which Are Larger Than the Wavelength Tend To Scatter More Light In the Forward Direction
Aerosol Which Are Smaller Than The Wavelength Tend To Scatter More Light At Side Angles
0
5
10
15
20
25 dV
/d(log(D
))
0.1 1 10 100 DIAM (um)
13
5
Accumulation Mode Aerosols Coarse Mode Aerosol
1E-2
1E-1
1E0
1E1
1E2
1E3P
HA
SE
FU
NC
TIO
N
0 50 100 150 SCATTERING ANGLE
FREETROP SULF(15%)VOG SULF.(75%) VOG+SALT(75%)
SALT(75%) SALT+LOWSULF(75%)
Calculated From Porter and Clarke (JGR, 1997) Sea Salt Aerosol Models
0.01 0.1 1 10 100
0.0
1.0x10-5
2.0x10-5
3.0x10-5
4.0x10-5
Original model unimodal genetic
inversions
dA
/dlo
g er,
m-1
radius, m
Genetic Inversion Approach To Derive Aerosol Size Distribution
(Lienert et al., Applied Optics, 2001)
0.1 1 10 100
0.0
1.0x10-5
2.0x10-5
3.0x10-5
Original model Genetic Inversions
dA
/dlo
g er,
m-1
radius, m
When One Aerosol Mode Dominates Then It Is Not Possible Retrieve It From Genetic Inversion
Winchester Design Polar Nephelometer (Optical Engineering, 1983)
1E-12
1E-10
1E-08
1E-06
0.0001
0.01
SC
AN
ING
RA
DIO
ME
TE
R
0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180
SCATTERING ANGLE OF SCAN RADIOMETER
BELLOWS BEACH (8-5-98) FILES 3,4,5ESTIMATED WIND SPEED 15-20 MPH
DARK MEASUREMENTS
5E-10
1.5E-09
2.5E-09
3.5E-09
4.5E-09
FIX
ED
AN
GL
E R
AD
IOM
ET
ER
20.5 20.55 20.6
TIME (hour)
BELLOWS BEACH (8-5-98) FILE1.DATESTIMATED WIND SPEED 15-20 MPH
Ground Based Polar Nephelometer
0 20 40 60 80 100 120 140 160 180
0.1
1
10
100
measured data inverted unimodal models
ang
ular
sca
tter
, ar
b. u
nits
scattering angle, deg
Overall Good Fit But Problems In Backscatter RegionField of View (FWHM ~ 4 deg.)
Complex Volcanic Aerosols At This Time !Non-Spherical Aerosol ?
Instrument Error (Variable Attenuation Filter)
0 20 40 60 80 100 120 140 160 180
0.1
1
10
100
m=1.40+0.001i
m=1.45
m=1.40
m=1.36
measured data unimodal models
ang
ular
sca
tter
, ar
b. u
nits
scattering angle, deg
0.01 0.1 1 10 100
0.0
1.0x10-5
2.0x10-5
3.0x10-5
4.0x10-5
5.0x10-5
6.0x10-5
measured sizer data
unimodal genetic inversion models
dA
/dlo
g era
diu
s,
m-1
radius, m
Aerosol Size Distributions Inverted From Polar NephelometerAerodynamic Particle Sizer
Conclusion
External Aerosol Polar Nephelometer Measurements Offer An Exciting New Way To Measure Aerosol Optical Properties In The Atmosphere
Although Current Measurements Have Been Encouraging, A Dedicated Measurement and Modeling Effort Is Needed
New Fiber Optic, Logarithmic Amplifier, and Calibration Techniques Now Offer Exciting Opportunities For Ground and Aircraft
Measurements