abstract_textpBroadband lightning signals are used to probe the D region ionosphere with a temporal resolution of 5 min and a spatial resolution of similar to 50 x 50 km. Together with a full wave propagation model, this technique allows determination of the reference height, h', and steepness parameter, beta, of an exponential electron density profile sensitive to the range of 10(6)-10(8) electrons/m(3). Daytime and nighttime background electron profiles away fromthunderstorms are presented, as well as profiles fromthree regions nearby and atop thunderstorms. The average daytime profile parameters are found to be h' = 67.7 km with a standard deviation of 0.9 km and beta = 0.7 km(-1) with a standard deviation of 0.1 km(-1). Average nighttime parameters are h' = 80.9 km with a standard deviation of 1.3 km and beta= 2.8 km(-1) with a standard deviation of 0.2 km(-1). Nighttime electron profiles nearby and atop thunderstorms show slightly higher values of h' (82.5-84.2 km) and significantly lower values of beta (0.9- 1.5 km(-1)). These findings indicate that there is significant electron depletion above similar to 80 km near and atop thunderstorms during the nighttime. Detailed analysis also shows substantial profile variations in space and time related to lightning discharges due to localized electron enhancement at high altitudes and reduction at lower altitudes. Nevertheless, the general depletion at higher altitudes appears to be related to the overall electrical behavior of the thunderstorm but not directly to lightning activity./p/abstract_text
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