Comparison of Lightning Channel Luminosity Versus Time Profiles in the Infrared and Visible Ranges.

Infrared (IR) luminosity of lightning channel in the 3–5 μm range usually persisted throughout the entire interstroke interval, which is in contrast to the simultaneously recorded visible (0.4–0.8 μm) luminosity that always decayed to an undetectable level prior to a subsequent return stroke pulse. A longer visible luminosity period at the end of flash tended to be associated with a longer IR afterglow period following the decay of visible luminosity (and by inference current) to an undetectable level. At the end of flash, the IR luminosity persisted up to about 1 s, and the median IR afterglow duration was a factor of 10 longer than the median visible luminosity duration. The IR luminosity often exhibited a hump when the visible luminosity was monotonically decaying or undetectable, with the corresponding channel temperature being likely around 3400 K. Plain Language Summary: Lightning is usually imaged in the visible (0.4–0.8 μm) range, although it also produces significant infrared (IR) emission. In this study, we compare, for the first time, the medium‐to‐far (3–5 μm) IR luminosity of lightning channels with the simultaneously recorded visible luminosity. The key findings include the persistent nature of IR luminosity throughout interstroke intervals, which is in contrast to visible luminosity that always decayed to an undetectable level before the following return‐stroke onset. After the last stroke, IR luminosity persisted much longer than visible luminosity. The IR luminosity often exhibited a hump when visible luminosity was monotonically decreasing or already undetectable. We inferred that the IR hump, occurring when the channel temperature decreases to a few thousand Kelvin, is associated with enhanced IR emission from nitric oxide molecules whose concentration is expected to be maximum around 3400 K. We also examined a number of factors influencing IR afterglow duration, such as the number of preceding strokes, return‐stroke peak current, and the occurrence of M‐components. This study contributes to the very limited literature on the IR emission from lightning and provides new insights into the dynamics of lightning channel cooling process. Key Points: In contrast to the visible, infrared (IR) channel luminosity between strokes usually persisted through the following return‐stroke onsetIR luminosity profile often exhibited an increase (hump) when the visible luminosity was monotonically decaying or undetectableAt the end of flash, IR luminosity persisted up to ∼1 s and its median duration was a factor of 10 longer than its visible counterpart [ABSTRACT FROM AUTHOR]