Distribution of ice particle surface roughness inferred from the multi-angle polarimetry by the POLDER

While ice clouds are ubiquitous, the maximum cloudiness is observed in the intertropical convergence zone (ITCZ) and the mid-latitude storm tracks. The updraft speed in clouds and the growth process of ice particles in these two regions are known to be different. Although in-situ measurements show distinct differences of crystal morphology between tropical and mid-latitude ice clouds, passive spaceborne measurements for quantifying the aforementioned differences at the global scale are scarce. In this presentation, we will illustrate an EOF-based method to quantify the particle overall shape and the degree of roughness with several independent variables. We also demonstrate the retrievals of these variables based on multi-angle polarimetric measurements (specifically, observations made by the Polarization and Directionality of the Earth's Reflectance (POLDER) instrument) in conjunction with radiative transfer simulations. In addition, data from Moderate Resolution Imaging Spectroradiometer (MODIS) and Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) are collocated to the POLDER data for identifying the cloud types and vertical structures. We show significant differences between tropical and extratropical ice clouds in the present retrievals. Furthermore, we discuss the effects of solar direction, satellite measurement angle, and cloud inhomogeneity on the retrieval differences.