Fundamental Cloud Microphysics Research

Cloud Microphysics photo

Examples of the 3D printed hailstones used in the experiments. Color coding represents density of the printing material. Blue: print density: 0.3 g m-3; purple: 0.4 g m-3; red: 0.5 g m-3; orange: 0.7 g m-3; white: 0.9 g m-3.

Over this past year, MMM scientists used novel approaches to estimate the fall characteristics of hail and the drag coefficients of lump and conical graupel. Three-dimensional scans of 60 hailstones of various sizes were printed and their terminal velocities were measured in the Johannes Gutenberg University, Mainz Germany, vertical wind tunnel. From these experiments, drag coefficients versus Reynolds numbers and Best number versus Reynolds number relationships were derived that covered a wide range of particle sizes. This information, together with the combined total of more than 2800 hailstones for which the mass and cross-sectional area were measured, were used to develop size-dependent relationships for the terminal velocity, mass flux and kinetic energy of realistic hailstones. A paper was published with collaborators from the Johannes Gutenberg University (Mainz, DE), the insurance Institute for Business & Home Safety (Richburg, SC) and Robert L Wright & Associates Inc. (Houston, TX).