Synergistic Studies of Raindrop Shapes, Oscillations and Orientations Using 2D-Video Disdrometer, Advanced Radar and Wind Tunnel

Colorado State University, Fort Collins CO

Investigators

Abstract

This research addresses a number of key science questions related to rain microstructure defined herein as the size, shape and orientation distributions of raindrops in a wide range of rain types and climatologies. Whilst great progress has been made in the understanding of drop size distribution variability, and there has been modest success in the use of "bulk" assumptions on mean drop shapes and orientation distributions, there are still variations in the raindrop shape distribution parameters and oscillation modes that are not fully understood. There are even fewer observations of the variability of the drop canting angle distribution. Knowledge of these rain microstructure characteristics is key to developing accurate polarimetric radar-based drop-size distribution and rain rate retrievals, and for electromagnetic wave attenuation-correction algorithms. This research is observationally-driven and makes use of multiple 2D-video disdrometers in different locations (Huntsville, AL and Brisbane, AU) and advanced radars including the dual-polarized ARMOR radar in Huntsville, AL; the dual-wavelength/dual-polarized CP2 radar in Brisbane, and the dual-polarized CSU-CHILL radar near Greeley, CO. The world class vertical wind tunnel facility at the Johannes Gutenberg-Universität in Mainz, Germany will be used for specialized observation of the time varying shapes and oscillation modes of freely "floating" drops, as well as an investigation into the time varying shapes of moderate-to-large drops after coalescing collisions with sub-millimetric sized drops. The broader impacts of the study are: (a) better use of new observing capability resulting from the imminent polarimetric upgrade of the National Weather Service operational weather radar network and "gap-filler" X band radars for short range hydrological applications; (b) incorporation of new results to improve radar displays used by many TV stations in the US that are planning to upgrade their C-band systems to dual-polarization to improve severe weather forecasting, and (c) use of results on drop shapes and orientations by the national and international radiowave propagation community.