Abstract
β=− Aexp () , where A is the coefficient in the relation VA D B = , D is the diameter of the rain drop, and ξ is a factor related to radar parameters and precipitation intensity. An examination of this exponential relationship between α and β shows that the radar experimental result was in excellent agreement with the theoretical prediction. From the observational results made with the Chung-Li VHF radar, we find that the value of β varied in the range 0.02 - 0.14, which is significantly different from the theoretical value of 0.07143. In addition, the β value is found to be positively correlated with the vertical air velocity, which is variable in nature. We, therefore, presume that the vertical air velocity seems to play a crucial factor in governing the change in the β value to explain the large scatter of the observed β values. The application of ξ value to the estimation of the precipitation intensity is also discussed in the text.
Highlights
It has been well recognized that a VHF radar has the advantage of accurately measuring a TAO, Vol 15, No 4, November 2004 number of crucial precipitation-related parameters that cannot be effectively observed by radars operated at other frequencies (Larsen and Rottger 1980; Wakasugi et al 1986; Chu et al 1991)
The meteorological radar operated at frequencies of C (6 GHz) or S (3 GHz) bands cannot sufficiently detect the weak echoes from the turbulent fluctuations of atmospheric refractivity, leading to difficulty in the measurement of the vertical air velocity
Radars operated at frequency lower than the VHF band will have difficulty detecting precipitation echo power owing to the appreciably small ratio of the diameter of the precipitation particle to the relatively long radar wavelength, causing fairly weak precipitation echoes that are indiscernible from clear air echoes in the observed Doppler spectrum
Summary
It has been well recognized that a VHF radar has the advantage of accurately measuring a. Aside from three dimensional wind velocity and turbulence intensity, a VHF radar can measure the terminal velocity of a raindrop by carefully removing the contribution of vertical air velocity from observed Doppler velocity, provided the Doppler components of clear air echoes and precipitation echoes can be generally discerned unambiguously. This capability makes a VHF radar capable of observing the true terminal velocity of a rain drop aloft (Chu et al 1991). The properties of α and β which are associated with atmospheric parameters, such as vertical wind velocity and the rainfall rate, are discussed in this article
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