Luminosity characteristics of lightning M components

A high-speed streak photograph of a natural cloud-to-ground lightning return stroke followed by two M components is analyzed. As opposed to the return stroke light pulse whose amplitude and waveshape vary markedly with height, the amplitude and waveshape of one M component light pulse is essentially invariant with height between the cloud base (about 1 km) and ground, while the other M component has a relatively constant light waveshape and a light amplitude that varies somewhat with height. The two M component light pulses, both occurring within about 0.6 ms of the return stroke pulse, exhibit a more or less symmetrical waveshape with a risetime and falltime of the order of many tens of microseconds. For one of the two M components a downward direction of propagation and a corresponding speed of the order of 10(8) m/s are inferred.