Systematic case studies of the phase partitioning in convective clouds with combined passive and active satellite observations

Abstract:

The thermodynamic phase of clouds has a large impact on their radiative properties and therefore on the energy budget of the earth. Nevertheless, the cloud phase distribution and glaciation processes are still poorly understood, which leads to large uncertainties in climate models. To improve the knowledge about the cloud phase and underlying processes, this study investigates the phase and microphyiscal properties of eight convective cloud cases using active and passive satellite measurements. The selection of cloud cases is based on a cloud tracking algorithm (Coopman et al., 2019), using measurements of the passive satellite instrument SEVIRI. A phase transition from liquid to ice of each cloud is required within the tracking algorithm. The vertical distribution of cloud phase and cloud properties is investigated with active satellite measurements of CloudSat and Calipso. Besides the CloudSat products, the DARDAR products are used as they combine both CloudSat and Calipso measurements and provide a larger accuracy in detection and phase determination due to different sensitivities. The evolution of the clouds can be investigated by the products of the passive instrument SEVIRI, which is onboard a geostationary satellite, while vertical profiles are available at a specific time steps from the polar orbiting satellites, boarding active instruments. Therefore, one vertical profile is available for each cloud case at a different timestep relative to its cloud top glaciation. The collocation of the different satellite observations leads to a detailed insight into cloud evolution, phase transition, and development of microphysical properties. The vertical structure of deep convective cells shows a decreasing ice particle size with height at cloud top, while the number concentration of the ice particles increases with height. Aggregation and sedimentation lead to the largest IWC in the middle part of the cloud. Comparing the investigated cases, a decreasing LWC and an increasing IWC is observed with the temporal evolution of convective clouds relative to the detected glaciation time. The effective radius of ice particles increases with time at lower heights and decreases at cloud top. In future work similar methods will be applied to other cloud systems, in particular mid-level clouds above the Southern Ocean.