Aerosol Characterization by Dual-Wavelength Polarization Lidar Measurements over Kochi, Japan during the Warm Seasons of 2008 to 2010

Dual-wavelength polarization lidar measurements of aerosols and clouds were conducted over Kochi (33.6°N, 133.5°E) during the warm-season field campaign of the Japanese Cloud Seeding Experiment Precipitation Augmentation project in June-July of 2008 to 2010. Lidar-derived aerosol optical properties were compared with the microphysical properties obtained with aircraft-based instruments to evaluate the utility of the lidar data for characterizing the background aerosol, which critically affects the success of cloud seeding to enhance precipitation. The results showed that the particle backscattering coefficient at 532 nm correlated well with the number concentration of aerosols with diameter (Dp) exceeding 0.3 μm (correlation coefficient, r = 0.89), whereas the correlation of the backscattering coefficient with the number concentration of cloud condensation nuclei (CCN), activated at a water saturation of 0.7% or 1.0%, was lower (r = 0.74) because of the low sensitivity of the lidar system to the small CCN particles (Dp ≈ 0.04 μm). In lidar data collected on 1 July 2008, the depolarization ratio (δ) was high (20%), and the backscatter wavelength exponent (å) was low (< 0.5) between altitudes of 4 and 6 km, and they were low (δ = 2.5%) and moderate (å = 0.7) between 0.5 and 1.0 km, suggesting the presence of supermicrometer-sized, non-spherical particles in the upper altitude range and a predominance of submicrometer-sized particles and/or spherical particles in the lower altitude range. These values were consistent with aircraft measurements, indicating the presence of supermicrometer-sized mineral particles in the upper altitude range and a predominance of submicrometer-sized sulfates and supermicrometer-sized sea-salt droplets at lower altitude. Our results demonstrate the utility of lidar data for aerosol characterization, although the further improvement of CCN characterization by lidar is necessary.