Lightning propagation and flash density in squall lines as determined with radar

Abstract

The propagation of lightning has been studied using radar techniques. The rise time of radar echoes is explained by ionized channel propagation through the radar beam. The calculated values agree well with those obtained experimentally. Measurements of the radial velocity of streamer propagation (along the antenna beam) show speeds of at least 2.5× 05 m/s. The time‐range variations in lightning echoes are indicative of (1) new ionization as streamers develop into different parts of the cloud, (2) channel decay during which adequate ionization exists for radar detection, or (3) continuing current. Lightning flash density has been determined for two squall lines, one in the USSR (using a 2‐m wavelength radar) and the other in the United States (using a 23‐cm wavelength radar). The United States study shows that the maximum lightning density tends to be near the leading edge of the precipitation cores in developing cells. As a cell in the squall line develops and the total lightning density increases, long discharges are produced, but shorter ones predominate. In contrast, as the cell dissipates, short flashes diminish or cease, and the long flashes dominate the lightning activity.