Effects of cirrus heterogeneity on lidar CALIOP/CALIPSO data

•Heterogeneous cirrus clouds are generated.•Lidar signals are simulated using a Monte-Carlo code.•Effects on CALIOP lidar measured data are evaluated.•Importance of horizontal photon transport is underscored.

The goal of this work is to evaluate the effects of cirrus heterogeneity on characteristics that are directly measured by the CALIOP/CALIPSO lidar, i.e. attenuated backscatter coefficient and depolarization ratio. This assessment was done using the 3D Monte Carlo simulator of Polarized Lidar signals (3DMcPOLID) together with the high-resolution 3D cloud fields-generator 3DCLOUD_V2. The evaluation is based on random sampling and on comparison between mean profiles of 3D clouds and of plane-parallel equivalent 1D clouds.Mean profiles of the apparent attenuated backscatter as well as of the integrated apparent backscatter are statistically equal when a cirrus cloud field is probed with the 325 m resolution. To the contrary, the difference between profiles is statistically significant in the case of the 1 km resolution. Profiles of the volume depolarization ratio are statistically different for both cases of the horizontal resolution. The total bias of CALIOP/CALIPSO lidar data is mainly due to the plane parallel bias and multiple scattering, i.e., horizontal photon transport.