CALIPSO level 3 stratospheric aerosol profile product: version 1.00 algorithm description and initial assessment

In August 2018, the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) project released a new level 3 stratospheric aerosol profile data product derived from nearly 12 years of measurements acquired by the spaceborne Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP). This monthly averaged, gridded level 3 product is based on version 4 of the CALIOP level 1B and level 2 data products, which feature significantly improved calibration that now makes it possible to reliably retrieve profiles of stratospheric aerosol extinction and backscatter coefficients at 532 nm. This paper describes the science algorithm and data handling techniques that were developed to generate the CALIPSO version 1.00 level 3 stratospheric aerosol profile product. Further, we show that the extinction profiles (retrieved using a constant lidar ratio of 50 sr) capture the major stratospheric perturbations in both hemispheres over the last decade resulting from volcanic eruptions, extreme smoke events, and signatures of stratospheric dynamics. Initial assessment of the product by intercomparison with the stratospheric aerosol retrievals from the Stratospheric Aerosol and Gas Experiment III (SAGE III) on the International Space Station (ISS) indicates good agreement in the tropical stratospheric aerosol layer (30 degrees N-30 degrees S), where the average difference between zonal mean extinction profiles is typically less than 25% between 20 and 30 km (CALIPSO biased high). However, differences can exceed 100% in the very low aerosol loading regimes found above 25 km at higher latitudes. Similarly, there are large differences (>= 100 %) within 2 to 3 km above the tropopause that might be due to cloud contamination issues.