Simulation of polarimetric radar variables in rain at S-, C- and X-band wavelengths

F Teschl,W L Randeu,R Teschl,M Schönhuber

doi:10.5194/adgeo-16-27-2008

F Teschl, W L Randeu + Show 2 more

Open Access

https://doi.org/10.5194/adgeo-16-27-2008

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Abstract

Abstract. Polarimetric radar variables of rainfall events, like differential reflectivity ZDR, or specific differential phase KDP, are better suited for estimating rain rate R than just the reflectivity factor for horizontally polarized waves, ZH. A variety of physical and empirical approaches exist to estimate the rain rate from polarimetric radar observables. The relationships vary over a wide range with the location and the weather conditions. In this study, the polarimetric radar variables were simulated for S-, C- and X-band wavelengths in order to establish radar rainfall estimators for the alpine region of the form R(KDP), R(ZH, ZDR), and R(KDP), ZDR. For the simulation drop size distributions of hundreds of 1-minute-rain episodes were obtained from 2D-Video-Distrometer measurements in the mountains of Styria, Austria. The sensitivity of the polarimetric variables to temperature is investigated, as well as the influence of different rain drop shape models – including recently published ones – on radar rainfall estimators. Finally it is shown how the polarimetric radar variables change with the elevation angle of the radar antenna.

Highlights

In polarimetric weather radar systems, relationships of the form R(KDP), R(ZH, ZDR), and R(KDP, ZDR) are generally used to estimate the rain fall rate R
At C-band the temperature can have influence on the polarimetric rainfall estimation algorithms; for example, at 5 cm wavelength resonance occurs for sizes larger than about 5 mm diameter, and several polarimetric observables exhibit non-monotonous dependence on the drop diameter (Zrnicet al., 2000)
The polarimetric radar observables ZH, ZDR, and KDP were calculated for 249 1-minute-rain episodes, observed with an imaging distrometer, the 2DVideo-Distrometer (Schonhuber et al, 1994), in the mountains of Styria, Austria

Summary

Introduction

In polarimetric weather radar systems, relationships of the form R(KDP), R(ZH, ZDR), and R(KDP, ZDR) are generally used to estimate the rain fall rate R. The main reason for the wide range of relationships is the drop-size distribution. At C-band the temperature can have influence on the polarimetric rainfall estimation algorithms; for example, at 5 cm wavelength resonance occurs for sizes larger than about 5 mm diameter, and several polarimetric observables exhibit non-monotonous dependence on the drop diameter (Zrnicet al., 2000). The polarimetric radar observables ZH, ZDR, and KDP were calculated for 249 1-minute-rain episodes, observed with an imaging distrometer, the 2DVideo-Distrometer (Schonhuber et al, 1994), in the mountains of Styria, Austria. The water volume of each rain drop and its equivolumetric sphere diameter is calculated from the recorded front- and side-view. The drop-size distribution was discretized in 0.25 mm steps of the equivolumetric sphere diameter Deq, and averages over 1 min have been considered.

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