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Analyzing the relationship between terminal velocity of raindrops and VHF backscatter from precipitation
 TAO
"... The exponential relationship between α and β in the expression V PT = α β was first found empirically by Chu et al. (1999), where VT is the mean Doppler velocity of the rain drop with respect to still air, and P is the rangecorrected VHF radar backscatter from precipitation. However, they did not p ..."
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The exponential relationship between α and β in the expression V PT = α β was first found empirically by Chu et al. (1999), where VT is the mean Doppler velocity of the rain drop with respect to still air, and P is the rangecorrected VHF radar backscatter from precipitation. However, they did not provide a theoretical explanation for this relationship. In this article, we will show theoretically that the mathematical relationship between α and β is indeed in an exponential form, namely, α ξβ = −Aexp ( ) , where A is the coefficient in the relation V ADB = , 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 ChungLi 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. (Key words: VHF radar, Drop size distribution, Terminal velocity)
Ka Band Propagation Experiments of Experimental Communication Payload (ECP) on ROCSAT1 – Preliminary Results
, 1998
"... It is recognized that rain attenuation is the primary factor in the degradation of Earthsatellite communication at the Ka band frequency. The beacon signal of the ROCSAT1 is set at 19.5 GHz for downlink and 28.5 GHz for uplink. ROCSAT1 is the low earth orbit (LEO) satellite with a circular orbit ..."
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It is recognized that rain attenuation is the primary factor in the degradation of Earthsatellite communication at the Ka band frequency. The beacon signal of the ROCSAT1 is set at 19.5 GHz for downlink and 28.5 GHz for uplink. ROCSAT1 is the low earth orbit (LEO) satellite with a circular orbit at the altitude of 600 km and 35 ° inclination angle and scheduled to be launched at the beginning of 1999. Given the extremely high frequency of the beacon, impairment of ROCSAT1 communications due to rain attenuation should be seriously considered. In this paper, the groundbased instruments for the Ka band propagation experiments of ROCSAT1, including ChungLi VHF radar, 19.5 GHz radiometer, optical rain gauge, automatic weather station, and disdrometer, are introduced. The spatial distribution of the longterm statistics of rainfall rate is analyzed in this paper on the basis of 8 years (19881995) rainfall rate data at oneminute time resolution, recorded by more than 70 tipping bucket rain gauges distributed over Taiwan island. It shows a pronounced latitudinal variation in
Negative correlation between terminal velocity and VHF radar reflectivity: observation and plausible explanation
"... Abstract. The correlation between precipitation backscatter P (or radar reflectivity Z) and reflectivityweighted terminal velocity Vt has long been thought to be positive. Namely, the larger the magnitude of the terminal velocity is, the stronger the radar reflectivity will be, and vice versa. Howe ..."
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Abstract. The correlation between precipitation backscatter P (or radar reflectivity Z) and reflectivityweighted terminal velocity Vt has long been thought to be positive. Namely, the larger the magnitude of the terminal velocity is, the stronger the radar reflectivity will be, and vice versa. However, we will show in this article the observational evidences of negative Vt–P correlation made with the ChungLi VHF radar. It is found that the negative Vt–P correlation can occur in the regions from close to ground to well above the melting layer. In addition, there is a strong tendency for the negative Vt–P correlation to occur around the bright band region. In light of the fact that the conventional model of single drop size distribution cannot explain this negative correlation, it is proposed that the drop size distribution responsible for the negative Vt–Z correlation is composed of two Gamma drop