Polarization lidar observations of aerosols and clouds at Manila (14.64 N, 121.07 E), Philippines

Polarization lidars transmit polarized laser pulses and collect both parallel, P/spl par/ and cross-polarized, P/spl perp/ backscatter. The degree of depolarization, D= P/spl par//P/spl perp/, depends on refractive index, size, phase and number density of the scattering medium. Lidar studies have shown values of D ranging from 0.02 to 0.04 in high number density of spherical liquid aerosols, due to multiple scattering, and values ranging from 0.4 to 0.7 in ice crystals. In some special cases, D may be zero and greater or equal to one in oriented crystals and complex crystals respectively. In the absence of aerosols and particles, Rayleigh scattering by air molecules generates a small amount of depolarization of about 0.014. Polarization lidars have proven to be an effective diagnostic tool in the assessment of cloud and aerosol properties. The paper aims to infer aerosol and cloud properties from extinction coefficient and depolarization measurements and extend the observations to the relationship between aerosol concentration and cloud characteristics, particularly in low-lying cloud layers. Aerosols are believed to feed clouds with nucleons necessary for condensation. Sulfate particles in particular act as CCN (cloud condensation nuclei); increasing the CCN may lead to more cloud droplets, hence high depolarization values in the cloud.