1. 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 Planetology University of Hawaii

2. Aerosol Phase Function Describes The Angular Distribution of Light Scattered By Aerosols.

3. Three Parameters Needed For Optical Calculations - Phase Functions - Absorption Coefficient - Scattering Coefficient How To Calculate the Phase Function ? For Simple Aerosols Mie Theory Works Well For 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 Measurements Of The Aerosol Phase Function Are Useful

4. 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

5. Accumulation Mode Aerosols Coarse Mode Aerosol

7. Calculated From Porter and Clarke (JGR, 1997) Sea Salt Aerosol Models

8. Genetic Inversion Approach To Derive Aerosol Size Distribution (Lienert et al., Applied Optics, 2001)

9. When One Aerosol Mode Dominates Then It Is Not Possible Retrieve It From Genetic Inversion

10. Winchester Design Polar Nephelometer (Optical Engineering, 1983)

13. Ground Based Polar Nephelometer

14. Overall Good Fit But Problems In Backscatter Region Field of View (FWHM ~ 4 deg.) Complex Volcanic Aerosols At This Time ! Non-Spherical Aerosol ? Instrument Error (Variable Attenuation Filter)

16. Aerosol Size Distributions Inverted From Polar Nephelometer Aerodynamic Particle Sizer

20. 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