Optical power and energy radiated by natural lightning

Abstract

[1] Calibrated measurements of the visible and near-infrared radiation produced by both negative and positive cloud-to-ground (CG) lightning strokes have been made at distances of 5 to 32 km in southern Arizona (AZ) and the central Great Plains using a photodiode sensor with a flat spectral response between 0.4 and 1.0 mm. Time-correlated video images (60 fps) of the channel development provided information about the types of strokes that were detected and reports from the U.S. National Lightning Detection Network indicated their locations, polarities, and estimates of their peak current. In our sample of negative strokes that were suitable for analysis, there were 23 first (or only) strokes (FS), 19 subsequent strokes that created new ground contacts (NGC), and 101 subsequent strokes that re-illuminated a preexisting channel (PEC). We also analyzed 10 positive strokes (in nine flashes), and 73 of the larger impulses that were radiated by intracloud discharges (CPs). Assuming that these events can be approximated as isotropic sources and that the effects of atmospheric extinction are negligible, the peak optical power (P o ), total optical energy (E o ), and characteristic widths of the sources (t cw = E o /P o ) have been computed. Median values of P o for negative FS, NGC, and PEC strokes were 1.8 Â 10 10 W, 1.1 Â 10 10 W, and 4.4 Â 10 9 W, respectively. Median values of E o were 3.6 Â 10 6 J, 3.5 Â 10 6 J, and 1.2 Â 10 6 J, respectively. The median characteristic widths of negative FS, NGC, and PEC strokes were 229 ms, 244 ms, and 283 ms, respectively. Positive CG strokes produced a median P o , E o , and t cw of 1.9 Â 10 10 W, 9.3 Â 10 6 J, and 497 ms, respectively. Estimates of the space-and-time-average power per unit length (' o ) in the lower portion of negative FS, NGC, and PEC channels had medians of 2.8 Â 10 6 W/m, 3.2 Â 10 6 W/m, and 1.4 Â 10 6 W/m, respectively, and the median ' o for four positive strokes was 8.8 Â 10 6 W/m. Median values for the estimated peak electromagnetic power (P EM ) radiated at early times in the strokes are 2.0 Â 10 9 W, 2.5 Â 10 9 W, 1.0 Â 10 9 W, and 9.1 Â 10 9 W for FS, NGC, PEC and positive strokes, respectively. CP events produced a median P o , E o , and t cw of 2.0 Â 10 9 W, 0.7 Â 10 6 J, and 311 ms, respectively, and are in good agreement with aircraft and satellite measurements. The values of P o , E o , and ' o for negative CG strokes in AZ are significantly larger than prior measurements in Florida, likely because there is less atmospheric extinction in our dataset, and due to extinction, all the above values of P o , E o , and ' o are lower limits at the source.

Optical power and energy radiated by return strokes in rocket‐triggered lightning

“…Table summarizes the number, N , of return strokes that were measured by each sensor in each year, together with the means, medians, and standard deviations of the vertical lengths of channel that were observed; the 10% to 90% risetimes of the current ( τ Ir ) and irradiance ( τ or ); the values of the peak current ( I p ) and the peak irradiance ( L pk ); the delay times between I p and L pk ; the values of ℓ o and ℓ R ; and the total charge that was transferred to ground ( Q ) during the initial 2 ms and the total optical energy per unit length ( J o ) in that interval. For comparison, Table also includes the NLDN estimates of the peak current and the values of ℓ o that were obtained by Quick and Krider [] for the subsequent return strokes in natural lightning that reilluminate a preexisting channel (PEC).…”

A leader‐return‐stroke consistent macroscopic model for calculations of return stroke current and its optical and electromagnetic emissions

“…The calculation is based on the current and conductance shown in Figure with equation in section 3.2. The light power peak is 99.1 MW/m when at the channel base and decays sharply to 9.6 MW/m when at 4.8 km high, which are comparable to the estimates of Guo and Krider [] and Quick and Krider []. The return stroke speed here is determined based on the median of the rising front of the light power waveform, which is very like that determined based on the current waveform as shown in Figure .…”

“…Both the current peak and its propagation speed attenuate exponentially as it propagates upward. All these results are qualitatively and quantitatively consistent with those reported in literature [ Guo and Krider , ; Quick and Krider , ; Shao et al ., ; Wang et al ., , ].…”

The changes on physical characteristics of lightning discharge plasma during individual return stroke process

“…22,23 In the process of natural lightning, the discharge current is positive correlated to the luminous intensity of the channel. 24 Therefore, the total intensity of spectra should be positive correlated to the return stroke current, so the profile of spectral line or the waveform of the total intensity can reflect the current waveform.…”