During a thunderstorm, scientists can map lightning by plotting where each bolt strikes the ground. For a more comprehensive picture, however, a lightning mapping array (LMA) uses closely spaced ground-based sensors to capture entire branching bolts in three dimensions. LMAs at several sites across the United States monitor high-frequency electromagnetic waves given off by lightning, providing valuable insights for weather forecasts in those locales. Researchers are now working out how best to use LMA data to illuminate the physics of lightning.
Furthering these efforts, Bruning and Thomas explored a new technique for estimating the total length of a branching flash of lightning. The approach builds on previous work—a quantitative analysis of the spectral distribution of lightning flash sizes—and employs calculations that rely on lightning’s fractal nature.
To test the new technique, the scientists used LMA observations of four lightning flashes in Colorado during the Deep Convective Clouds and Chemistry field campaign. They compared their fractal-based calculations to a manual connect-the-dots method, both of which relied on LMA data. When instrument measurement errors occurred—common at long ranges and less sensitive LMAs—the fractal method was more reliable at estimating the total length of each branching bolt.
The impact of this new method could reach beyond short-term weather predictions: When lightning strikes, it splits nitrogen molecules in the air, creating nitric oxide (NO), which quickly forms nitrogen dioxide (NO2). Nitrogen oxides are a precursor to ozone, which acts as a greenhouse gas in the upper troposphere, thus influencing global temperatures.
Traditionally, scientists have estimated nitrogen oxide production by simply counting lightning flashes. However, more recently, researchers have tried to account for the distribution of flashes of different sizes. Thus, the ability to make better calculations of lightning bolt length could improve nitrogen oxide estimates and lead to more accurate climate forecasts. (Journal of Geophysical Research: Atmospheres, doi:10.1002/2015JD023766, 2015)
—Sarah Stanley, Freelance Writer
Citation: Stanley, S. (2015), How long is a bolt of lightning?, Eos, 96, doi:10.1029/2015EO038693. Published on 4 November 2015.