The statistical analysis of 15-yrs of observations (1951-1965) of the occurrence and duration-time of thunderstorms was based on data from 13 meteorological stations, located in different climatic regions of Poland. This study was completed with data obtained from several of our measurements of air ionization, and with an analysis of data published in the Annals of the Geophysical Observatory in Swider. These data included the electric conductivity of the air, the number of condensattion nuclei and records of the potential gradient of the electric field in the atmosphere near the ground. The values which characterize the temporal and spatial distribution of thunderstorms activity as well as other parameters representing the electric properties of the atmosphere are shown in tables and figures. In general, the occurrence frequency of thunderstorms, both frontal and thermal types, reaches a annual maximum in the months June and July in most meteorological stations. In the diurnal (24-hrs) cycle the occurrence frequency of thunderstorms has two peak values: in the late afternoon about 17.00-19.00 hr and the secondary maximum in the evening (21.00-22.00 hr) and a minimum in the morning. In the Carpathianmountain region a maximum frequency of thunderstorms was noted usually between 13.00-16.00 hr. Diurnal fluctuations of thunderstorms activity are particularly large in mountain regions, at orographically different locations of meteorological stations, with a distinct maximum peak in the afternoon. In some parts of the mountain regions, for example, those situated in valleys, less thunderstorm activity was noted. Every thunderstorm can be considered as a huge electrostatic generator in the atmosphere, influencing the course of electric processes and the occurrence of electric phenomena in the atmospheric environment. During thunderstorm-periods (near thunderstorms < 4 km) the highest fluctuations of ions concentration, polarity and shifts in ionic spectrum and sudden, great changes of electric field potential and fluctuations of electric conductivity of the air were recorded. The concidence of these changes with “disturbed”; weather situations, which proved to be meteorotropic in our medical-meteorological investigations seems to suggest, that considerable changes of electric processes and properties of the atmosphere may belong to the category of biotropic factors.
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