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Koichiro Wakasugi
,
Akiyoshi Mizutani
,
Masaru Matsuo
,
Shoichiro Fukao
, and
Susumu Kato

Abstract

Raindrop size distribution and vertical air velocity are directly derived from VHF Doppler radar spectra in precipitation environments. As was first proposed by Wakasugi et al., we use a least-squares fitting parametric estimation for VHF Doppler spectra to determine the distribution and air motions. After discussing further the VHF Doppler spectrum method, especially the effects of spectral broadening mechanisms, the method is applied to Doppler spectra obtained during the seasonal rain front (Bai-u front) observation in Japan. Variations of vertical air velocity and distribution parameters are discussed, based on this longer period dataset.

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Koichiro Wakasugi
,
Akiyoshi Mizutani
,
Masaru Matsuo
,
Shoichiro Fukao
, and
Susumu Kato

Abstract

In precipitation environments, sensitive VHF Doppler radars have a capability to detect echoes from both refractive index irregularities and precipitation particles. The purpose of this paper is to propose a direct method to estimate the drop-size distribution N(D), the mean vertical air velocity and turbulence using Doppler spectra obtained by VHF Doppler radars. Bemuse the new method directly estimates turbulence as well as the mean vertical air velocity, the N(D) parameters, deduced from a least-squares fit approach, are free from cmrs inherent in conventional measurements using microwave Doppler radars. Temporal and spatial variations of N(D) and mean vertical air velocity during a cold front passage are then studied to demonstrate the capability of the present method.

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Koichiro Wakasugi
,
Ben B. Balsley
, and
Terry L. Clark

Abstract

The VHF Doppler radar has become a powerful tool for probing structures and motions of the clear air. In this paper, we discuss the capability of VHF radar as a tool for cloud and precipitation studies. Large fluctuations of refractive index from the cloudy air can be anticipated because of an abundance of water in clouds. Due to the difficulties in obtaining the necessary fine-scale observational data within clouds, we base our analysis of cloud-echoing properties on the numerical simulation of nonprecipitating cumulus by Klaassen and Clark. The Bragg scatter echo intensity is estimated from the temperature and humidity fields obtained from the cloud model. We find that the echo is enhanced at the boundary between the cloud and environment because of enhanced water vapor fluctuations. Although echoes from nonprecipitating clouds can be detected by UHF and VHF radars, only VHF radars can discriminate echoes due to large precipitation particles from the Bragg scatter echo of cloudy air. With UHF radars, the precipitation echoes totally mask the Brag scatter echoes.

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