End-of-storm oscillation in tropical air mass thunderstorms

Abstract

Characteristics of the end-of-storm oscillation (EOSO) in the atmospheric surface electric field observed beneath isolated air mass thunderstorms at a tropical station, Pune, are investigated. Typically, the value of the electric field at the ground during the EOSO periods has been observed to range between -3 and +4 kV m^-1. Durations of the EOSO at Pune are 24% of those for the large quasi-stationary thunderstorms occurring at Florida and 55% of the convective air mass thunderstorms at New Mexico. During the EOSO periods, frequency of lightning decreases very much but some flashes exhibit unique features of charge transportation associated with them. Observation of a new phenomenon, the inverted EOSO, is reported in a storm with inverted polarity of electrical dipole. Our observations are found to be consistent with the convective mechanism scenario of the EOSO in which the surface field meters are exposed to the upper positive charge of the cloud by the downdrafts.