Comparison of Results Obtained with the VIDIAZ Spectropluviometer and the Joss-Waldvogel Rainfall Disdrometer in a “Rain of a Thundery Type”

In this paper the mean values of the raindrop size distribution n(D), rainfall rate R, liquid water content W and radar reflectivity Z obtained by two different instruments are compared: a spectropluviometer which measures the diameter and fallspeed of each raindrop, and a Joss-Waldvogel disdrometer which gives the diameter by measurement of the force of the impacting drops on a sensor, assuming that they fall at the terminal velocities in still air obtained by Gunn and Kinzer. For 14 measurements of 1 min each in a rain of a thundery type, it is found that the fallspeeds of raindrops are about 13–1% above the values of Gunn and Kinzer in the range of the measured diameters (0.8–2.8 mm) for the Joss-Waldvogel disdrometer these fallspeed deviations produce a correction of ∼12% on R and 17% on W and Z. Introducing these corrections for the disdrometer and a correction due to the fact that some raindrops were not recorded by the spectropluviometer (and, in addition, taking into account the statistical errors resulting from the natural fluctuations of the rain) R, W and Z a common range of values for these two instruments.