D-layer electron profiles observed with substantial spatial and temporal change near thunderstorms

Broadband lightning signals are used to probe the D-layer ionosphere with a temporal resolution of 5 minutes and a spatial resolution of ~50 x 50 km. Together with a full wave propagation model, this technique allows determination of the reference height, h, and steepness parameter, β, of a typical exponential electron density profile. Daytime and nighttime background electron profiles away from thunderstorms are presented as well as profiles from three regions nearby and atop thunderstorms. The average daytime profile parameters are found to be h = 68 × 1 km and β = 0.7 × 0.1 km-1, and average nighttime parameters are h = 81 × 1 km and β = 2.7 × 0.2 km-1. Nighttime electron profiles parameters very near to and atop a mesoscale thunderstorm show slightly higher values of h (81 - 85 km) and significantly lower values of β (0.7 - 2.3 km-1). Within 200 km of a smaller storm, h = 83.6 × 1.1 km and β = 1.0 × 0.3 km-1. These profiles indicate that there is a significant electron enhancement at lower altitudes near and atop thunderstorms, up to 103 electrons/m3 at 60 km during the nighttime. The results also suggest that the enhancement is a result of the overall electrical behavior of the thunderstorm, and does not correspond directly to lightning activity.