Inter-comparison of Above-Cloud Aerosol Observation from OMI and CALIOP

Abstract:

The above-cloud-aerosol (ACA) phenomena, wherein significant active-based scattering and passive-based radiances are induced by particles above what are predominately lower tropospheric clouds, has garnered significant recent scientific interest due to potential impacts on regional radiation and satellite-based cloud property retrievals. Rigorous uncertainties in ACA event occurrences and climatological observations have not yet been established, however. Using collocated Ozone Monitoring Instrument (OMI) aerosol products, Moderate Resolution and Imaging Spectroradiometer (MODIS) cloud products, and simultaneous cloud and aerosol observations from the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP), we compare and contrast passive versus active methodologies, respectively, for resolving ACA. An inter-comparison of spatial ACA distributions and global ACA trends derived from both methods is described. Regional ACA trends are derived, along with their statistical significance, for nine regions found susceptible to ACA. We find that the use of both techniques is necessary, as each exhibits strengths and weaknesses. For example, the passive-based method is only capable of detecting UV absorbing aerosols However, whereas CALIOP can profile and segregate aerosol and cloud, OMI’s wide swath provides a significant gain in observational volume due to CALIOP’s inability to scan off nadir.