Validation of CIPS Version 5.20 PMC Data

Abstract The Cloud Imaging and Particle Size (CIPS) instrument operated onboard the NASA Aeronomy of Ice in the Mesosphere (AIM) satellite from April 2007 to March 2023. CIPS was a nadir‐viewing UV imager that made global measurements of scattered sunlight at high spatial resolution. These measurements were capable of discriminating the scattering of UV solar photons from Polar Mesospheric Cloud (PMC) ice particles against the background sunlit atmosphere at multiple coincident scattering angles, providing a direct measurement of the PMC ice scattering phase function. These measurements were used to retrieve a suite of critical PMC data products including cloud frequency, albedo, mean particle radius, and ice water content. The CIPS data set covers 15 complete PMC seasons in each hemisphere. In this paper we describe and validate the final archived PMC data version, v5.20r08. The version 5 retrieval algorithms represent a complete overhaul of the previously published version 4 data. These changes were implemented to allow for a consistent set of retrievals using data from multiple CIPS measurement sequences adopted in response to the changing AIM orbit geometry. We summarize the CIPS measurement sequences and sampling, describe the improvements in the version 5 data and give a detailed comparison of the v4.20 and v5.20 data sets. The v5.20 cloud frequencies are then compared to measurements from the Advanced Himawari Imager full disk imaging instrument, providing a mutual validation of the two data sets. Taken together, these results demonstrate the high quality and scientific validity of the CIPS v5.20 PMC data products.