Experiments in Rainfall Estimation with a Polarimetric Radar in a Subtropical Environment

Abstract

A unique dataset consisting of high-resolution polarimetric radar measurements and dense rain gauge and disdrometer observations collected in east-central Florida during the summer of 1998 was examined. Comparison of the radar measurements and radar parameters computed from the disdrometer observations supported previous studies, which indicate that oscillating drops in the free atmosphere have more spherical apparent shapes in the mean than equilibrium shapes. Radar-disdrometer comparisons improved markedly when using an empirical axis ratio relation developed from observational studies and representing more spherical drop shapes. Fixedform power-law rainfall estimators for radar reflectivity (Z H ), specific differential phase (K DP ), specific differential phase-differential reflectivity (K DP , Z DR ), and radar reflectivity-differential reflectivity (Z H , Z DR ) were then determined using the disdrometer observations. Relations were produced for both equilibrium shapes and the empirical axis ratios. Polarimetric rainfall estimators based on more spherical shapes gave significantly improved performance. However, the improvement was largely in bias mitigation. Rainfall estimates with the Z H -Z DR measurement pair had the highest correlation with rain gauge observations, the smallest range in bias factors from storm to storm, and the smallest root-mean-square error.

Dual-polarization radar rainfall estimation in Korea according to raindrop shapes obtained by using a 2-D video disdrometer

“…We compared the new axis-ratio experimental fit with existing mean axis-ratio relations such as those of Pruppacher and Beard (1970), Beard and Chuang (1987), and Brandes et al (2002) (see Fig. 5).…”

“…Polarimetric parameters are sensitive to the DSD properties. Rainfall rates estimated from polarimetric radar measurements are affected by the mean shape of raindrops and canting (Brandes et al, 2002).…”

“…Some researchers have attempted to produce the mean shape of raindrops. Keenan et al (2001); Brandes et al (2002); Thurai and Bringi (2005); and Marzuki et al (2013) derived empirical relations from observational data, and Pruppacher and Beard (1970); Green (1975), and Beard and Chuang (1987) investigated the shape of raindrops falling under the influence of gravity. These raindrop axisratio relations play an important role in the derivation of polarimetric radar rainfall algorithms that use Z DR and K DP (Jameson, 1983(Jameson, , 1985Gorgucci et al, 2001).…”

“…Specifically, three raindrop shape assumptions (Pruppacher and Beard, 1970;Beard and Chuang, 1987;Brandes et al, 2002) and the newly derived axis-ratio relation from 2DVD data were used to derive polarimetric rainfall retrieval algorithms. The Z H and Z DR biases of Bislsan dualpolarization radar were calibrated by comparing them with simulated Z H and Z DR values obtained from the 2DVD.…”

Long‐term monitoring of French polarimetric radar data quality and evaluation of several polarimetric quantitative precipitation estimators in ideal conditions for operational implementation at C‐band

“…In summary, the 10 algorithms that have been included in the evaluation exercise are: (Z h , Z h cor ,Z dr cor Φ dp , K dp , r hv ) + Type Advection R algorithm with attenuation correction; • The Beard and Chuang (1987) R-K dp : R = 29.7K 0.85 dp ; • The Brandes et al (2002) R-K dp : R = 33.8K 0.79 dp ; • A hybrid Z h -K dp algorithm with a 0.5 • km −1 K dp threshold; • A hybrid Z h -K dp algorithm with a 1 • km −1 K dp threshold.…”