RAMAN LIDAR MEASUREMENTS OF AEROSOL EXTINCTION AND BACKSCATTERING - 2- DERIVATION OF AEROSOL REAL REFRACTIVE-INDEX, SINGLE-SCATTERING ALBEDO, AND HUMIDIFICATION FACTOR USING RAMAN LIDAR AND AIRCRAFT SIZE DISTRIBUTION MEASUREMENTS

Aerosol backscattering and extinction profiles measured by the NASA Go ddard Space Flight Center Scanning Raman Lidar (SRL) during the remote cloud sensing (RCS) intensive operations period (IOP) at the Departme nt of Energy Atmospheric Radiation Measurement (ARM) southern Great Pl ains (SGP) site during two nights in April 1994 are discussed. These p rofiles are shown to be consistent with the simultaneous aerosol size distribution measurements made by a PCASP (Passive Cavity Aerosol Spec trometer Probe) optical particle counter flown on the University of No rth Dakota Citation aircraft. We describe a technique which uses both lidar and PCASP measurements to derive the dependence of particle size on relative humidity, the aerosol real refractive index n, and estima te the effective single-scattering albedo omega(0). Values of n ranged between 1.4-1.5 (dry) and 1.37-1.47 (wet); omega(0) varied between 0. 7 and 1.0. The single-scattering albedo derived from this technique is sensitive to the manner in which absorbing particles are represented in the aerosol mixture; representing the absorbing particles as an int ernal mixture rather than the external mixture assumed here results in generally higher values of oo. The lidar measurements indicate that t he change in particle size with relative humidity as measured by the P CASP can be represented in the form discussed by Hanel [1976] with the exponent gamma 0.3 +/- 0.05. The variations in aerosol optical and ph ysical characteristics captured in the lidar and aircraft size distrib ution measurements are discussed in the context of the meteorological conditions observed during the experiment.