Computer processing for deriving drop‐size distributions and vertical air velocities from VHF Doppler radar spectra

Abstract

A fully automated data processing procedure has been developed for deriving the precipitation parameters from VHF Doppler radar spectra simultaneously with the background atmospheric parameters such as the mean wind velocity. The procedure has largely enhanced our capability in analyzing the data from continuous observations, which was hardly possible with human-attained analysis. The accuracy of the derived parameters are quantitatively evaluated by means of numerical simulations. It is found that the rain parameters can be determined with an accuracy of 15% at a time and height resolution of 10 min and 600 m, respectively, for high signal-to-noise ratios, for example. Parameters for the background atmospheric turbulence are estimated with an accuracy more than twice the fitting procedure currently used to analyze clear-air data. Experimental results of the MU radar observations are compared with the rain intensity measured on the ground for the first time. It is confirmed that the radar has a capability of measuring rain parameters with a rainfall rate sensitivity of about 1 m.m h-1. 961

VHF signal power suppression in stratiform and convective precipitation

“…In this situation the signal power will be overestimated and the spectral width may not be interpreted in terms of turbulence intensity without further analysis (Chu and Lin, 1994). It should be noted that more complicated processing schemes can be used to attempt to separate the characteristics of any precipitation signal from the clear air signal (Sato et al, 1990). An algorithm similar to that used in Rajopadhyaya et al (1994) is used in Sect.…”

Meso-β to -γ-Scale Wind Circulations Associated with Precipitating Clouds near Baiu Front Observed by the MU and Meteorological Radars

“…Information of the precipitation echo of the MU data is available for the estimation of the drop-size distribution (DSD) in the precipitating cloud (e.g., Wakasugi et al 1986Wakasugi et al , 1987Sato et al 1990), and only the vertical distribution of the precipitation echoes is discussed in this study. The top level of the precipitation echoes may be almost coincident with the melting layer or so-called bright band altitude (a layerr with temperature-0C) inside a stratiform cloud, whereas the precipitation echoes above the freezing level may be produced by solid precipitation particles with large fall velocities, which had grown in strong updrafts.…”

Hierarchical Structures of Vertical Velocity Variations and Precipitating Clouds near the Baiu Frontal Cyclone Center Observed by the MU and Meteorological Radars

“…The left-hand side panels of Fig. 1 show an example of results of the automatic spectral fitting obtained by using the procedure developed by Sato et al (1990) for vertical Doppler velocity spectra near the melting layer (at 4.58-5.03km altitudes in this case). In general the raindrops grow rapidly within some hundreds of meters below the melting layer, but this short vertical to the observed echo power spectra at 4.58-5.03km altitudes.…”

“…1, a spectrum of Doppler velocity for the zenith (vertical) direction at in a lower altitude (4.58km altitude in this case) has two peaks, and the left (negative velocity) and right (close to zero velocity) spectral peaks are due to raindrop and atmospheric motions, respectively. In earlier studies, Sato et al (1990) have developed the numerical technique to extract the atmospheric echo from an observed echo spectrum including the raindrop echo, by fitting automatically the echo spectrum to a bimodal model function with the non-linear least-square method. Then we can express the observed echo spectrum by a sum of two monomodal spectra induced by purely atmospheric and raindrop echoes.…”