Optical emission and peak electromagnetic power radiated by negative return strokes in rocket-triggered lightning

• Calibrated optical power emitted by rocket-triggered lightning is reported.
• Poynting power computed at time of current peak using transmission-line model.
• The ratio of optical to Poynting power is 5% at the time of current peak.
• Poynting power loss may not be negligible at the beginning of return strokes.

Calibrated measurements of the optical radiation produced by negative return strokes in rocket-triggered lightning (RTL) have been made in the visible and near infrared (VNIR) spectral region in correlation with currents measured at the channel base. Using a simple transmission-line model, the currents have been used to estimate the peak electromagnetic (EM) fields and Poynting power that are radiated in the time-domain (i.e. from about 1 kHz to 3 MHz). The results show that the optical power radiated by RTL at the time of the peak current has a mean and standard deviation of 130±120 MW, a value that is only about 5% of the Poynting power that is radiated into the upper half-space at that time. These results are in good agreement with similar measurements made on the subsequent return strokes in natural lightning that remain in a pre-existing channel. Our methods and assumptions are similar to those of (Guo and Krider, 1982 and Krider and Guo, 1983; Quick and Krider, 2013).