Characterizing continuing current lightning using multi instrument observations

Lightning flashes with continuing current (CC) are a type of cloud-to-ground (CG) flash that pose significant risks, including air quality degradation, damage to electrical systems and the igniting of wildfires.  Understanding CC lightning is important for mitigating its effects and assessing its potential connection to climate change.

In this study, we used a combination of space-based instruments (ASIM and GLM) and ground-based networks (ENTLN and ELF) to systematically identify CC lightning across the Contiguous United States (CONUS) from June 1, 2018, to December 31, 2021.

ASIM, aboard the International Space Station, provides high-resolution optical measurements at dual wavelengths (337.0 nm and 777.4 nm), while GLM offers continuous geostationary monitoring of optical emissions at 777 nm. Ground-based systems like ENTLN and ELF provide complementary radio data.

We utilized two distinct methods to classify lightning flashes as CC or no CC. The first relied on the predictive models of Fairman and Bitzer (2022), based on the optical signal of GLM, while the second utilized a metric derived from Extreme Low Frequency (ELF) magnetic signals.

We found clear differences between optical properties in ASIM dual-wavelength (337.0~nm, 777.4~nm) light curves associated with CC and no CC lightning, indicating potential for identifying CC flashes using ASIM optical recordings.

Results reveal optical and electromagnetic differences between CC and no CC lightning. First, CC flashes have longer-lasting optical emissions, higher power densities, and elevated total energy levels compared to no CC flashes. Second, the processed ELF radio signal can sense the presence of CC and the electrical polarity of lightning flashes. These findings highlight the value of combining space-based optical and ground-based ELF measurements to improve detection and classification of CC lightning.