FDTD Study of Ionospheric Reflections Associated With Consecutive Strokes of the Same Lightning Flash

Ground-level electric fields generated by four consecutive strokes in a negative cloud-to-ground lightning flash at a horizontal distance of 176 km from the field observation point, including both the ground wave and the first ionospheric reflection (skywave), are computed using the finite-difference time-domain (FDTD) method in the 2D cylindrical coordinate system. The lightning return-stroke is represented using the modified transmission-line model with linear current decay with height (MTLL) and the modified transmission-line model with exponential current decay with height (MTLE). Parameters of the exponential atmospheric conductivity profile providing the best match to the corresponding measured daytime electric fields are found. The best-match parameters are not much influenced by the choice of return-stroke model (MTLL or MTLE), the ground conductivity (σgr= ∞, 10 mS/m or 1 mS/m), the propagation speed of current wave along the lightning channel (v= 2c/3,c/2 orc/3 wherecis the speed of light), or the height of the channel in the MTLL model (H= 7 km or 5 km).