Aerosol retrieval from dual-wavelength polarization lidar measurements over tropical pacific ocean and validation of a global aerosol transport model

Spatial distributions of water-soluble, sea-salt and dust aerosols over the Tropical Pacific Ocean were analyzed from shipborne, dual-wavelength polarization Mie-scattering lidar measurements. The shipborne measurements by the R/V MIRAI were conducted over the Tropical Pacific Ocean in 2001, 2004, and 2006. We used an algorithm to retrieve the extinction coefficients for water-soluble, sea-salt and dust particles from the three-channel lidar data, i.e., the return signals at wavelengths of 532 and 1064nm and the depolarization ratio at a wavelength of 532nm. The results revealed that the water-soluble and sea-salt particles existed in the planetary boundary layer formed below about 1.5km for all the observation periods. Dust particles were scarcely present for any observation periods. The optical thicknesses of water- soluble particles were relatively large over the Pacific Ocean between Japan and New Guinea and in the eastern Indian Ocean, indicating transport of pollutants from the land. Furthermore we evaluated the global aerosol transport model SPRTNTARS using the retrieved aerosol extinction coefficients and the observed lidar signals at wavelengths of 532 and 1064nm for the 2001 observation period. We found rough agreement for the general pattern of the three aerosol components. However, the model underestimated the extinction coefficients for water-soluble particles by about 75% (0.03km^-1 in extinction coefficient) on average for the observation period. In contrast, the model overestimated the extinction coefficients for sea-salt by about 200 % on average for the observation period. However, the difference in the extinction coefficient itself for sea-salt is small, about 0.01km^-1. The lidar signals simulated from the model outputs for aerosol and clouds revealed underestimations of 37% (50%) at a wavelength of 532nm (1064nm) on average for the observation period.