Middle atmosphere electric fields above a Γ-shaped stroke

We describe the space-time distribution of the pulsed electric field in the middle atmosphere above a positive Γ-shaped lightning stroke. The current wave moves initially vertically and turns horizontally afterwards. Radiation arrives from the vertical electric dipole followed by that of the horizontal dipole. Combined with reflection from the perfectly conducting ground, the source generates three subsequent pulses in the atmosphere with the mutual lag depending on the velocity of the current wave. Pulses are multiply reproduced by reflections from the ionosphere and ground. The non-stationary fine structure appears in the spatial distribution of electric field, which persists for 2 ms and more. Estimates indicate on possible bunching of free electrons in the mesosphere. Focusing may occur at 10 km distance being delayed by a few ms from the moment of electron-field interaction.