![]() The estimator for mean raindrop shape from radar measurements is developed and its accuracy and sensitivity are evaluated in section 4. Section 2 defines the mean shape model for raindrops, whereas section 3 describes the effect of raindrop shape on polarimetric radar measurements. The objective of this paper is to derive an algorithm to estimate the mean shape of raindrops from polarimetric radar data. It would be very useful to obtain an estimate of the mean shape–size relation from polarimetric radar measurements in order to study any variability in the mean shape of the raindrops in different storms as well as different regions of storms. The above results were obtained after careful and tedious analysis of aircraft-mounted 2D imaging probe data. (1998) showed that the axis ratios were higher than the model given by (1) for D 4.5 mm the mean axis ratios were smaller than those given by (1). The experimental results of Bringi et al. (1)In addition, nonlinear relations are available to model axis ratios of raindrops ( Andsager et al. A commonly used approximation relating the axis ratio of a raindrop to the diameter is given by ( Pruppacher and Beard 1970):ī a D. All of the above studies as well as polarimetric radar measurements at multiple polarizations show that the shape of raindrops can be approximated by an oblate spheroid, described with an axis ratio ( b/ a) and equivolumetric spherical diameter D, where a and b are the major and the minor axes of the drop, respectively. (1998) were fairly consistent with the model results of Beard and Chuang (1987). The experimental results of Chandrasekar et al. The shapes of raindrops have been studied theoretically by Green (1975) and Beard and Chuang (1987), experimentally in wind tunnels by Pruppacher and Beard (1970), and in natural rainfall using aircraft probes by Chandrasekar et al. The equilibrium shape of a raindrop, falling at its terminal fall speed, is determined by the balance between the forces due to surface tension, hydrostatic pressure, and aerodynamic pressure from airflow around the drop. The mean shape raindrop also plays an important role in the development of algorithms to estimate rainfall rate and liquid water content based on reflectivity factor ( Z H), differential reflectivity ( Z DR), and specific differential propagation phase ( K DP). The mean shape of raindrops plays a critical role in the interpretation of the polarimetric radar measurements. The data referring to a flash flood that occurred over Fort Collins were collected by the Doppler and polarimetric CSU–CHILL radar (d) Observed shape–size relation for the values of mean β̂ computed for the reflectivity intervals corresponding to 40 53 dB Z. The data referring to a flash flood that occurred over Fort Collins were collected by the Doppler and polarimetric CSU–CHILL radar. (c) The mean value of the estimate β̂, signed by star, and the corresponding standard deviation for reflectivity intervals 40–45, 45–50, and 50–53 dB Z and for reflectivity greater than 53 dB Z. (b) Histogram of observed values of the estimate β̂, computed by (12), for reflectivity factor ranging between 45 and 50 dB Z. ![]() (a) Histogram of observed values of the estimate β̂, computed by (12), for reflectivity factor ranging between 40 and 45 dB Z. ![]()
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