Rainfall Rate and Electric Charge and Size of Raindrops of Six Spring Showers

Abstract

Two ground-based instruments were designed and built in order to accomplish the present research. The first, based on the principle of the induction ring, measures the electric charge as well as the size of the individual raindrops. The other is a novel raingage providing the instantaneous value of the rainfall rate: a U-shaped tube turns the rainwater flow into an airflow more easily measured by a sensitive airflow meter. The adjustable range has been set between 1 and 100 mm h?1. Six spring showers were investigated. Individual electric charges between 5 and 100 pC have been measured on raindrops up to 4 mm in diameter. The data reduction shows that each shower must be studied separately, using several parameters. Under these conditions, there are two distinct types of precipitation, according to the sign of the charge excess they provide. The total charge carried down by each shower is primarily determined by the greater number of drops of one sign as compared to the other sign. Cross-correlation coefficients have been calculated between the charge and the size of each drop, on one hand, and between the intensity of the shower and the electric charge carried down, on the other. It appears that, for one kind of shower the larger the drops, the more negative the charge they carry. Moreover, when the rainfall rate increases, so does the mean charge of the charged drops, regardless of the sign. The results seem to agree with the inductive charging mechanism as well as with selective ion capture within the cloud.