Aerosol layers over the Pacific Ocean: Vertical distributions and optical properties as observed by multiwavelength airborne lidars

[1] Scattering properties of tropospheric aerosol layers were observed with airborne lidars during the Global Backscatter Experiment (GLOBE) airborne campaigns covering a wide range of latitude and longitude over the Pacific Ocean. Lidar data at 0.532, 1.064, 1.54, and 9.25 mum wavelengths are used to study the vertical profiles and optical properties of the marine boundary layer (MBL) as well as elevated dust layers due to transport of material from Asia. The lidars were calibrated to provide absolute aerosol backscatter coefficients at their respective wavelengths. The lidar data are compared with predictions based on commonly used dust and sea salt aerosol refractive index and size distribution parameters. Published observations of aerosol characteristics from onboard in situ sensors are used to verify locations where mineral dust aerosol dominated the aerosol optical properties in the free troposphere. Relative humidity has a major impact on the observed MBL aerosol scattering characteristics. The multiwavelength observations of the dust layers are consistent with the assumption that for the particle size range that dominates the scattering properties the particle size distribution varies little over 10 3 km transport distances and is not strongly dependent on altitude. A nonsphericity effect on the dust scattering, in particular the suppression of backscattering at the shorter lidar wavelengths, is discussed in the context of data comparisons with model predictions. The observations of the sea salt aerosol scattering in the remote MBL indicate that at altitudes above 150 m in optically clear conditions the influence of the supermicron coarse mode is minor compared with that of the submicron accumulation mode.