Surges Superimposed on Continuing Currents in Lightning Discharges

M components are impulsive processes that occur during continuing currents following return strokes in both natural and rocket-triggered lightning. Similar impulsive processes occur during the initial stage of rocket-triggered lightning and during the initial stage of upward natural lightning initiated from tall objects. The combination of impulsive and steady current components may represent an additional threat to various objects and systems. For example, M components may impart electrodynamic stresses on metallic structural elements already weakened due to thermal effects of the background continuing current. It is possible that the very large positive currents measured by K. Berger and co-workers on instrumented towers were associated with M-component type processes.