Lightning channel length and flash energy determined from moments of the flash area distribution

Abstract

A widely used approach in observational and modeling studies of NO x produced by lightning is to relate NO x production to the number of flashes, without regard for the distribution of lightning flash sizes. Recent studies have begun to consider channel length and flash size, which is now observable with VHF Lightning Mapping Array data. This study uses a capacitor model for flash energy based on the flash coverage area, which defines a size scale. This flash area is then filled with channel using a fractal method and compared to other methods that estimate length directly from the VHF source locations. In the presence of instrument measurement errors, area-and fractal-based estimates are shown to be more stable estimators of flash length than connect-the-dots approaches and therefore are better suited for comparison to NO x production. A geometric interpretation of using vertical profiles of VHF source density to weight the altitude distribution of total channel length is developed. An example of the time series of moments of the lightning flash size distribution is shown for an example case, and some meteorological interpretation is given.

Spatio-temporal dimension of lightning flashes based on three-dimensional Lightning Mapping Array

“…Even if there is reliable evidence of durations exceeding 1 s (e.g. Lang et al, 2016;Bruning and MacGorman, 2013;Bruning and Thomas, 2015;Montanyà et al, 2014b), the present results suggest to keep 1 s as the time period as the maximum time period, as almost 95% of the analysed sample is below 1 s.…”

Airborne quantification of upper tropospheric NOx production from lightning in deep convective storms over the United States Great Plains

“…Thus, we also consider NO x production as a function of the flash area. Here we calculate the sum of all flash areas (in 2 min intervals), where the sum is proportional to the total flash energy [ Bruning and Thomas , , Appendix C]. A cumulative flash area, in units of square kilometers, is determined for the relevant time period of each storm and represents the sum of the flash areas from the onset of lightning (blue dashed line in Figure ) until the departure of the aircraft from the storm (second gray dashed line in Figure ).…”

“…Therefore, this study uses LMA data within 200 km. Further processing sorted the LMA data into flashes, as described by Bruning and MacGorman [] and Bruning and Thomas []. This study uses counts of the total number of lightning flashes (IC + CG flashes), as well as the areas of those flashes.…”

Time Evolution of Satellite‐Based Optical Properties in Lightning Flashes, and its Impact on GLM Flash Detection

“…LMA sources were clustered into flashes using the approach described in section 2.5. The flashes were then used to estimate flash area, channel length and flash extent using a convex hull flash object described in Bruning and MacGorman (2013) and Bruning and Thomas (2015). The flash area is defined as the hull area, and flash extent is defined as major axis length of the convex hull.…”