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The lightning swept stroke along an aircraft in flight. Part I: thermodynamic and electric properties of lightning arc channels

During a lightning strike to an aircraft in flight, the lightning channel becomes deformed in the airflow and displaced along the aircraft, a so-called swept stroke. The deformation and the displacement are caused by the interaction between the aerodynamic flow and the plasma properties of the channel together with the properties of the surface. The main part of the lightning current is a continuous current with a magnitude of hundreds of amperes and a duration of hundreds of milliseconds. The objective of this article is to analyse the properties of the lightning channel during this continuous current phase in order to parametrize them; this parametrization is used in a companion paper (Larsson et al J. Phys. D: Appl. Phys. 33 1876-83) for complete swept-stroke simulations. A model of the thermodynamic evolution of a lightning channel during its continuous current phase is developed and numerically solved. In this model, the channel is assumed to have axial symmetry. A quantitative analysis of the influence of failing axial symmetry is also included. The main conclusions are that the steady-state conditions are rapidly reached and that the channel can be considered to be a free-burning arc subjected to increased thermal losses due to transverse aerodynamic flow.