A Study on the Relation between Terminal Velocity and VHF Backscatter from Precipitation Particles Using the Chung-Li VHF Radar

Abstract

The relationships between the mean Doppler terminal velocities VT of the hydrometeors with different phases and the range-corrected VHF backscatter P from the corresponding precipitation particles are investigated by using the Chung-Li VHF radar. The radar precipitation data employed for the analysis were taken from four independent experiments conducted on different weather conditions. They show that the observed α and ? values in the power-law approximation VT = αP? above the melting layer are generally smaller than those below the layer, while in the bright band the values of ? (α) are enormously smaller (greater) than those above and below the bright band. Theoretical analysis shows that the mathematical relationship between α and ? can be approximated very well by a simple exponential function, which is in excellent agreement with the observations. A new method for estimating the coefficient A and exponent B in the fall speed?diameter relationship V(D) = ADB with respect to still air on the basis of the theoretical relation between α and ? is also proposed. A comparison of the estimations of A and B with those reported in the literature indicates that the former are smaller than the latter. The authors believe that the difference in the two is due to the different types of the clouds producing the precipitation. In addition, it is found that the value of A is proportional to the height of the 0°C isotherm, implying that the air temperature plays a role in establishing the relationship between the fall speed and the diameter of the hydrometeors.