Entrainment and Freezing Processes in Tropical Convective Clouds during EC-TOOC

• Applicant: Professor Dr. Bernhard Mayer
• Subject Area: Atmospheric Science
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 502206049

Clouds are an essential part of the Earth’s climate by affecting the radiation budget, hydrological cycle, and global circulation. Especially the Tropics, which cover the transition from shallow cumuli in the trade-wind regions to deep convective clouds in the inner-tropical convergence zone, are considered a key factor. Improving our understanding of the interactions of clouds and circulation in this subsystem of the climate is a primary goal of the EC-TOOC campaign, to which the efforts described in this proposal will contribute. By deploying our multipurpose hyperspectral cloud imager specMACS on the research aircraft HALO, we plan to contribute to the overarching goals of EC-TOOC by providing measurements of the cloud morphology and cloud microphysical processes. Specifically, we plan to use specMACS’ two-dimensional RGB imagery to reconstruct the three-dimensional cloud boundary and its motion, ice fraction profiles retrieved from specMACS’ spectral radiance observations, and observations of the cloud bow and backscatter glory, which reveal the mean (liquid) droplet size and its variance at the cloud edge. Furthermore, specMACS will provide important two-dimensional information, such as the cloud mask required for interpreting other instruments’ observations during EC-TOOC. Our measurements will also serve as validation for the shortwave channels of EarthCARE/MSI. We will use our measurements to improve the understanding of the turbulent mixing process of clouds with their environment. This process is essential to predict the development of clouds, as entrainment typically decreases their buoyancy, while detrainment preconditions the environment for subsequent thermals. Specifically, we want to analyze the statistical properties of the cloud boundary motion, which we expect to relate to key features of the turbulent mixing process (turbulence kinetic energy, regions of preferential entrainment or detrainment). Furthermore, we plan to use the three-dimensional cloud boundary to analyze its geometrical properties and scaling behavior, where scale breaks are expected to relate to changes in the mixing character (homogeneous vs. inhomogeneous mixing). The impact of mixing on mixed-phase clouds is largely unknown, but is expected to influence glaciation of the cloud and hence cloud optical properties and precipitation production. Accordingly, we plan to analyze how the cloud ice fraction changes with height. By focusing on the influence of the droplet size distribution, which is partially shaped by the turbulent mixing process, we will be able to provide important information for the model representation of the glaciation process, as the droplet size distribution width is typically not predicted in current microphysical models.

• DFG Programme: Infrastructure Priority Programmes
• Subproject of: SPP 1294: Atmospheric and Earth System Research with the "High Altitude and Long Range Research Aircraft" (HALO)
• Co-Investigators: Dr. Fabian Hoffmann; Dr. Tobias Zinner