Experimental study of polarization characteristics of lidar signal in case of occlusion front

Abstract

In this work, experimental data of a light detection and ranging (lidar) polarization study of cloud formations in a case of warm occlusion front in winter are presented. The changes in the low clouds at the different stages of the front advection are followed: before, during and after the cold air mass settles down. The experiment was carried out using a polarization lidar with variable viewing angle of the receiver, which allows the influence of the multiple scattering on the signal depolarization to be estimated. The data are acquired by simultaneously recording two polarized components of the lidar return: parallel and perpendicular with respect to that of the sounding radiation. The depolarization coefficient of the signals from various clouds types (stratus, stratocumulus, nimbus stratus, etc.) is determined by receiving and rejecting the multiply scattered lidar returns. The depolarization of the lidar returns is determined also in the space between the ground and the clouds base during different stages of the front advection including wet snowfall and no precipitation; the typical values obtained are: 3–5% before precipitation, 5–7% during rain, 10–40% during snowfall and 1–2% after precipitation. Conclusions are drawn about the phase composition of the clouds formations and the heights of the ice crystals nucleation during snowfall. So the evolution of the atmospheric formations is followed during the different stages of the warm occlusion front advection.