Some observations and characteristics of lightning ground discharges in southern Ontario

Abstract

Abstract Lightning ground flash and stroke observations were made with a single‐station gated, wideband magnetic direction‐finding system with a nominal range of 180 km located in Southern Ontario during the May‐September lightning‐active seasons of 1982 and 1983. Information was recorded on the azimuth of arrival, time, amplitude, stroke multiplicity and order, and polarity. The local climatology and seasonal statistics of lightning are analysed and summarized, and compared with standard observations of thunderstorm days and hours. Regional daily flashing rates and extremes for periods of 5 to 60 min were found to have a good empirical relationship. About 15% of the flashes had multiple strokes, generally less than 10 but with as many as 14 strokes. About 8% of the flashes were positive discharges; 3% of these were multistroke with no more than 2 strokes. The lightning activity exhibits well defined diurnal peaks in the afternoon and at night 1–3 h before sunrise. The time interval between strokes was found to have a lognormal distribution with modal and median values of 60 and 75 ms, respectively, and no significant dependence on the order of stroke. The stroke‐to‐stroke amplitude changes within the same flash show that subsequent stroke amplitudes are often greater than the first. Subsequent strokes follow many patterns of change, the most common being an amplitude oscillating with ascending stroke order. The multistroke flash duration median values rose from about 80 ms for 2‐stroke flashes to about 650 ms for 8‐stroke flashes. Under certain assumptions of system detection efficiency and range limits a regional ground flash density of 1.62 and 2.44 km−2 a−1 was estimated for the two years.