HR: 14:40h
AN: H53J-05    [Abstracts]
TI: Oscillations of Raindrops Captured by High-speed Imaging
AU: * Testik, F Y
EM: Firat.Testik@gmail.com
AF: Duke University, Civil and Environmental Engineering Department, Pratt School of Engineering, Duke University , Durham, NC 27708 United States
AU: Barros, A P
EM: Ana.Barros@duke.edu
AF: Duke University, Civil and Environmental Engineering Department, Pratt School of Engineering, Duke University , Durham, NC 27708 United States
AU: Bliven, L F
EM: Francis.L.Bliven@nasa.gov
AF: NASA-GSFC, Wallops Flight Facility, Wallops Island, VA 23337 United States
AB: A raindrop falling at terminal velocity is not always at steady-state, but may oscillate around its equilibrium shape. To measure the characteristics of raindrop oscillations, earlier studies have utilized different methods such as photographing the backscattered light from the primary rainbow or comparing the mean chord ratios of the observed drops and equilibrium drops. Based on these indirect methods, it is generally agreed that raindrop oscillation modes are primarily axisymmetric, transverse, and horizontal modes of fundamental harmonic predicted by linear theory. In this study, we present unique direct observations of periodic raindrop oscillations in a light rain-shower (1.2 mm/h) using a high-speed video camera of 1000 frames per second. These images show the existence of an oscillation mode with the same frequency as the fundamental harmonic, but with different shape than that predicted by linear theory. The authors propose that the identified oscillation mode is the result of interacting modes due to the nonlinear effects associated with large amplitude oscillations. Lateral drift with a speed of approximately 20-30 % of the drop terminal velocity and without a preferred direction is induced by these oscillations. These experiments serve as an insightful illustration of the potential benefit of applying high-speed imaging technology to investigate the dynamical microstructure of rainfall at the raindrop scale.
DE: 1853 Precipitation-radar
DE: 1854 Precipitation (3354)
DE: 1895 Instruments and techniques: monitoring
DE: 3354 Precipitation (1854)
SC: Hydrology [H]
MN: Fall Meeting 2005