Advanced Comprehensive Analysis of Rain Drop Shapes, Oscillation Modes, and Fall Velocities Using High-Resolution Surface Disdrometers, Polarimetric Radar, and Numerical Models

Colorado State University, Fort Collins CO

Investigators

Abstract

Raindrops do not stay in a constant state as they fall towards the surface. They can change shape, size, and speed. Weather radars can measure some of these aspects, but need to rely on assumptions about others. This project will combine observations of droplets with numerical modeling to provide researchers a better idea about how many of each size of drops there are, how the drops interact when they collide, and how the radar views the droplets. The result will be better data for the estimation of precipitation from radars, which impacts flood forecasting and hydrology. The project will also provide training opportunities for students, the next generation of scientists. The research team will combine observational analysis with numerical models in order to increase the accuracy and completeness of rain drop sizes, oscillations, and fall speeds. Knowledge of these quantities will enable a new evaluation of the importance of collisional-forcing of drop oscillation in moderate-to-intense rain rates. The observations and modeling will also allow the PIs to create new "drop-by-drop" calculations of scattering matrices and polarimetric radar observables. The observational part of the project will take place at a highly instrumented site near the University of Alabama-Hunstville campus. The main instruments to be used will be the Meteorological Particle Spectrometer, for imaging and measurement of small drops, and the low-profile 2D-video disdrometer (2DVD) for overlap and larger drops. Modeling work will consist of extending the "drop-by-drop" scattering methodology to include both symmetric and asymmetric shapes, the latter computations to be based on advance method-of-moments surface-integral-equation techniques.