Using CALIPSO's ocean surface lidar return signal and AMSR-E wind fields to determine oceanic aerosol type distributions

Oceanic aerosol loading and type have implications for ocean productivity/health, atmospheric radiative transfer, air-quality models and forecasts, and such biogeochemical processes as ocean iron fertilization. CALIPSO aerosol subtyping studies have shown that most natural and anthropogenic aerosol types are found over the ocean with varying frequency and abundance. The aerosol types found over the ocean span a wide range of radiative impacts from highly absorbing (biomass burning smoke) to highly scattering (non-seasalt sulfates, seasalt, some dusts etc). Since marine aerosol transport and generation phenomena are impacted by the wind patterns and continental sources, the aerosol types over the ocean tend to be regional and have significant differences in optical characteristics over the remote oceans and coastal regions. Relationships between wave slope variance and wind speed, based on comparison between CALIPSO lidar sea surface backscatter and collocated Advanced Microwave Scanning Radiometer for the Earth Observing System (AMSR-E) wind speed measurements have been established by Hu et al (2007). In this study, we use collocated sea surface backscatter measurements from CALIPSO and AMSR-E wind speed measurements to determine atmospheric column optical depth over the ocean. We then derive the aerosol column optical depth and use it to constrain the CALIPSO lidar attenuated backscatter measurements to derive lidar ratios. Aerosol lidar ratio is an intensive property and is related to aerosol type. The lidar ratios derived from the column optical depth are matched to known aerosol models obtained from AERONET observations to obtain global aerosol subtype distributions. Mapping the aerosol subtype distributions over the oceans will improve the wind speed retrieval from the lidar surface signal since atmospheric attenuation by aerosols contributes the largest uncertainty. CALIPSO has been in orbit long enough to obtain type segregated seasonal and zonal oceanic aerosol distributions for use in studies of ocean productivity and dust aerosol fluxes to the oceans. These results are compared to CALIPSO’s conventional aerosol subtyping products.