Field Studies of Raindrop Oscillations With Applications to Radar Meteorology
Tokay, Ali
This item is only available for download by members of the University of Illinois community. Students, faculty, and staff at the U of I may log in with your NetID and password to view the item. If you are trying to access an Illinois-restricted dissertation or thesis, you can request a copy through your library's Inter-Library Loan office or purchase a copy directly from ProQuest.
Permalink
https://hdl.handle.net/2142/72452
Description
Title
Field Studies of Raindrop Oscillations With Applications to Radar Meteorology
Author(s)
Tokay, Ali
Issue Date
1993
Doctoral Committee Chair(s)
Beard, Kenneth V.
Department of Study
Atmospheric Sciences
Discipline
Atmospheric Sciences
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Physics, Atmospheric Science
Abstract
The characteristics and causes of raindrop oscillations were studied from two field experiments in Hawaiian and Illinois showers. The former experiment (HaRP) focused on the onset of raindrop oscillations as well as oscillations frequencies of small raindrops, whereas the latter experiment (ISWS) had a broader purpose to investigate the oscillation characteristics of moderate-to-large size raindrops including amplitudes as well as frequencies, and oscillation causes.
Raindrop oscillations were found to start at a diameter of d = 1.0 to 1.1 mm in both HaRP and ISWS experiments, consistent with 1991 laboratory observations of Beard, Kubesh and Ochs and with the expected onset of eddy shedding. Most of the oscillation frequencies ($>$95%) were near the fundamental harmonic (f$\sb2)$ with only a few observed near the first harmonic (f$\sb3)$ in both experiments. The oscillation frequencies around the fundamental harmonic showed a size dependency that crossed the theoretical value for f$\sb2$ at about d = 1.5 to 1.6 mm. The oscillation amplitude measurements determined from the vertical extent of the dash streaks showed good agreement with the 1988 data of Sterlyadkin, whereas the oscillation amplitudes estimated from the distortion indicated somewhat larger values for d $>$ 2mm. Eddy shedding was found to be the most likely cause of small raindrop oscillations because of the onset oscillations near 1.0 mm and weak forcing by drop collisions, turbulence, and wind shear.
The influence of raindrop oscillations on dual-polarization radar parameters was investigated for the observed and theoretical size distributions using axis ratios based on four different sets of calculations and measurements. Differential reflectivity (Z$\sb{\rm DR})$ decreased by as much as 0.74 dB from its value for non-oscillating raindrops. Similar change caused by raindrop oscillations were also found for the other dual-polarization parameters, such as the circular and linear depolarization ratios (CDR, LDR), differential phase shift ($\phi\sb{\rm DP}),$ and differential specific attenuation $(\delta$A).
Use this login method if you
don't
have an
@illinois.edu
email address.
(Oops, I do have one)
IDEALS migrated to a new platform on June 23, 2022. If you created
your account prior to this date, you will have to reset your password
using the forgot-password link below.
