Differing current and optical return stroke speeds in lightning. Issue 7 (1st April 2014)

• Record Type: Journal Article
• Authors: Liang, C.; Carlson, B.; Lehtinen, N.; Cohen, M.; Marshall, R. A.; Inan, U.
• Is Part Of: Geophysical research letters. Volume 41:Issue 7(2014:Apr.)
• Page Start: 2561
• Page End: 2567
• Publication Date: 2014-04-01
• Subjects: return stroke -- current wave speed -- optical radiation wave speed -- electrodynamics -- thermodynamics; Geophysics -- Periodicals; Planets -- Periodicals; Lunar geology -- Periodicals; 550
• DOI: 10.1002/2014GL059703
• Languages: English
• ISSNs: 0094-8276

Abstract

Abstract : During the return stroke in downward negative cloud‐to‐ground lightning, a current wave propagates upward from the ground along the lightning channel. The current wave causes rapid heating of the channel and induces intense optical radiation. The optical radiation wave propagation speed along the channel has been measured to be between 1 5 and 2 3 of the speed of light. The current wave speed is commonly assumed to be the same but cannot be directly measured. Past modeling efforts treat either the thermodynamics or electrodynamics. We present the first model that simultaneously treats the coupled current and thermodynamic physics in the return stroke channel. We utilize numerical simulations using realistic high‐temperature air plasma properties that self‐consistently solve Maxwell's equations coupled with equations of air plasma thermodynamics. The predicted optical radiation wave speed, rise time, and attenuation agree well with observations. The model predicts significantly higher current return stroke speed. Key Points: Study both the electrodynamics and thermodynamics of the return stroke channel The relationship between the current and optical wave is highly nonlinear The current wave speed is significantly higher than the optical wave speed