Improvements to CALIOP Aerosol Detection and Subtyping in Recently Released Version 4, Level 2 Products

After a decade of observations, the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) instrument on board the CALIPSO satellite continues to provide an unprecedented record of the vertical structure of aerosols in the Earth’s atmosphere. This presentation describes the improvements to CALIOP aerosol detection and subtyping algorithms embodied in the new version 4 level 2 products, released in fall 2016. The new version of level 2 products capitalize on improved level 1 calibration procedures and the adoption of MERRA-2 reanalysis product, which provides a higher fidelity representation of atmospheric state than the GMAO FP-IT dataset used in version 3. We will demonstrate how these two changes allow detection of fainter aerosol layers in the troposphere. Additionally, we will show that aerosol and cloud discrimination has improved with version 4.

This presentation will highlight substantial improvements to the CALIOP aerosol subtyping algorithm in version 4 level 2. In this algorithm, tropospheric aerosol layers are classified into subtypes such as dust, smoke, marine and so on, depending on their optical and geometric properties. The aerosol subtypes are in turn used by the CALIOP extinction retrieval algorithms to ascribe lidar ratios that are typical for the aerosol type. We will summarize how lidar ratios assumed for several CALIOP aerosol subtypes have been revised in version 4 to reflect the current state of knowledge. Further, a new tropospheric aerosol subtype has been introduced representing mixtures of dust and marine aerosol which were misclassified as polluted dust in version 3. This presentation will demonstrate how these improvements cause version 4 to better represent the three dimensional distribution, extinction profiles and optical depths of key aerosol subtypes relative to the previous version 3 level 2 products.

Additionally, stratospheric aerosol subtypes are now reported in version 4 level 2, including volcanic ash and sulfate. The presentation will describe how these aerosol types are identified and elucidate the limitations of the stratospheric aerosol subtyping algorithm. Case studies and monthly statistics of volcanic events will be shown to illustrate the utility of these new stratospheric subtypes.