Study on the Evolution Characteristics of the Return Stroke Spectra and Channel Temperatures by Using Two Spectrographs with Different Time Resolution

<p>Temperature is one of the crucial parameters reflecting the energy and current transfer&nbsp;characteristics in the lightning discharge channel.&nbsp;According to the spectra of&nbsp;six lightning return strokes recorded simultaneously by two high-speed slit-less&nbsp;spectrographs with different time resolutions, the spectral&nbsp;intensity and&nbsp;temperature evolution of the return stroke channels over&nbsp;time was quantitatively analyzed.&nbsp;The spectral characteristics show that&nbsp;the ionic&nbsp;line intensity decayed rapidly with time as the current&nbsp;declined, while the atomic line intensity decreased more slowly. Additionally, it is found that ionic lines&nbsp;existed&nbsp;in the spectra of continuing current&nbsp;process for up to hundreds of microseconds. It further indicates&nbsp;that the ionic line intensities are &nbsp;associated with the discharge currents and that their radiation mechanism is closely related to the collision&nbsp;excitation under the action of strong currents.&nbsp;The temperature calculated by&nbsp;the&nbsp;ionic&nbsp;lines&nbsp;can reflect the thermodynamic properties of the current-carrying channel.&nbsp;The temperature calculated&nbsp;using&nbsp;atomic lines is significantly&nbsp;lower than that calculated by the ionic lines in the same spectrum. The radiation mechanism for majority of the atomic lines&nbsp;differs from&nbsp;that of the ionic&nbsp;lines.&nbsp;During the continuing current,&nbsp;the channel temperatures&nbsp;calculated by both ionic&nbsp;lines&nbsp;and&nbsp;atomic&nbsp;lines&nbsp;showed&nbsp;a&nbsp;similar evolution feature&nbsp;which&nbsp;declined&nbsp;slowly or even basically unchanged.&nbsp;This property reflects the persistent&nbsp;heating effect of the current.</p>