Z-R relation of heavy rainfall

Routine meteorological radar service adopts Z=200R^<1.6> relation in converting Z (radar reflectivity factor) to R (rainfall intensity). The relation is obtained as the average form of various rains, and is fit for long lasting weak rain. Z is calculated by the rain drop size distribution (N_D) in rain cloud. The spectrum form of N_D shows remarkable change in each individual storm. It is known that great error of R between the radar and the actual is often seen in cases of convectively developed rain systems. This paper discusses the Z-R relation of heavy rain. We are scarse of N_D spectrum of heavy rain because its observation chance is quite few. The N_D estimation method by 10 minute rainfall data is used for reconstructing the heavy rain N_D. The heavy rainfall data of Nagasaki event are analyzed. The reconstructed N_D is characterized by the abundant population of diameter 2-4 mm raindrops. This is quite similar to the heavy rain N_D observed actually in Kyushu. Heavy rain N_D of Nagasaki event makes Z=1537R^<1.10>. The radar can estimate only half of rainfall amount with Z=200R^<1.6> setting.