Abstract
The lidar on the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) mission, makes robust measurements of dust and has generated a length of record that is significant both seasonally and inter-annually. We exploit this record to determine a multi-year climatology of the properties of Asian and Saharan dust, in particular seasonal optical depths, layer frequencies, and layer heights of dust gridded in accordance with the Level 3 data products protocol between 2006 and 2016. The data are screened using standard CALIPSO quality assurance flags, cloud aerosol discrimination (CAD) scores, overlying features and layer properties. To evaluate the effects of transport on small-scale phenomena such as morphology, vertical extent and size of the dust layers, we compare probability distribution functions of the layer integrated volume depolarization ratios, geometric depths and integrated attenuated color ratios near the source to the same distributions in the far field or transport region. To evaluate the uncertainty in the lidar ratios, we compare the values computed from dust layers overlying opaque water clouds, considered accurate, with the constant lidar ratio value used in the CALIOP algorithms for dust
Highlights
Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) is collaboration between NASA and Centre National d’Études Spatiales (CNES), was launched in April 2006 to provide vertically resolved measurements of cloud and aerosol distributions [14; 15]
Asian dust AOD peaks in March-May lead the Saharan dust AOD peaks by 3 months Saharan dust emissions are approximately 40% stronger than Asian Dust if AOD is used as a proxy for emissions
Lidar measurements of Saharan and Asian dust optical properties near source regions and during transport have been used to study the evolution of dust as it mixes with other pollutants during transport
Summary
CALIPSO is collaboration between NASA and Centre National d’Études Spatiales (CNES), was launched in April 2006 to provide vertically resolved measurements of cloud and aerosol distributions [14; 15]. The primary instrument on the CALIPSO satellite is the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP), a nearnadir viewing two-wavelength polarization-sensitive instrument. Dust directly forces the radiative balance by absorbing and scattering radiation, and indirectly by acting as cloud condensation nuclei and ice nuclei. It alters the atmospheric heating profiles in such a way that it impacts cloud distributions. The deployment of CALIPSO has enabled vertically resolved measurements of dust and provides significant insights into properties of Saharan and Asian dust aerosols. The depolarization measurements enable the discrimination between ice clouds and water clouds [5] and the identification of nonspherical aerosol particles [7]. CALIPSO’s measurements of dust properties are robust and the length of the record is significant both seasonally and inter-annually
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