The Kinetic Energy of Hailfalls. Part II: Radar and Hailpads

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Abstract
The kinetic energy of hailfalls is measured with a 10 cm radar. For comparison of the results a total of 204 hailpad stations was used covering an area of 780 km2, i.e., one pad per 3.8 km2. The experimental setup is such that the largest distance between any hailpad and the radar is less than 30 km. The radar is accurately calibrated with raindrop disdrometers and hailstone spectrometers. The radar data consist of PPI pictures obtained at a constant elevation angle of 5.5° with a time resolution of 1 min and a reflectivity resolution of 5 dBZ. The radar reflectivity values are transformed into kinetic energies by means of empirical Z–Ė relations obtained from measured time-resolved hailstone spectra. The data of six severe hailstorms are studied and the following results are obtained: 1) The correlation coefficient of corresponding hailpad and radar derived kinetic energies at single points of a hailstorm is 0.7, a value which can be increased to 0.8 if four-point averages are taken; 2) the global kinetic energy Eg(Z) of a hailfall calculated from radar data agrees to better than 20% with the corresponding value Eg deduced from hailpad information; and 3) the agreement between Eg(Z) and Eg of a hailstorm is better than a few percent for the two cases for which individual Z–Ė relations are available.

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