Studying mixed-phase cloud microphysical processes using cloud radar Doppler spectral moments

Description

Previous observations demonstrate that a considerable fraction of low-level Arctic stratus clouds contains volumes composed of both water and ice (i.e., mixed phase). Although mixed-phase clouds are prevalent in the Arctic, quantifying the liquid phase within these clouds using remote sensors is a challenge. As a result, a complete understanding of the microphysical and dynamical processes that shape the formation and evolution of mixed-phase clouds is lacking. Ground-based remote sensors are important for monitoring and studying clouds and their microphysical, macrophysical, and dynamical processes. The complexities of clouds demand multiple remote sensor measurements in their study. Data from a millimeter-wavelength cloud radar (MMCR) and a high spectral resolution lidar (HSRL) collected during the Mixed-Phase Arctic Cloud Experiment (M-PACE) on the 6th and 12th of October 2004 are used to characterize Arctic stratus clouds, including their liquid component. The HSRL is employed to distinguish cloud-hydrometeor phases and determine cloud bases because of its excellent sensitivity to cloud droplets and its ability to detect changes in polarization. Because HSRL signals can be completely attenuated by cloud droplets short distances above cloud base, the possibility of using moments of MMCR Doppler spectra to identify, separate, and quantify the liquid contribution to the total reflectivity is investigated. We use theoretical (i.e., Gaussian-shaped) and measured multimodal Doppler spectra to retrieve liquid and ice phases and their evolution as a function of height. These results are used to identify and interpret different microphysical processes operating within Arctic mixed-phase clouds.