Continental-Scale Lightning Observations at High Frequency

We initiated high-frequency (HF, 3–30 MHz) lightning observations to remotely study lightning processes using skywave propagation. HF lightning skywaves were detected at distances up to 3,300 km (potentially farther) during both day and night, with over 64% of events having peak currents below 50 kA. HF measurements revealed distinct temporal features of negative cloud-to-ground (CG) leaders, narrow bipolar events, and negative breakdown following positive return strokes. Unlike VLF and LF methods, which primarily capture current pulses along lightning channels, HF observations detect both transient and prolonged leader emissions. This provides more equal sensitivity to both in-cloud (IC) and CG events, potentially benefiting IC/CG classification and studies of IC-associated phenomena such as terrestrial gamma-ray flashes. Ionospheric conditions may influence HF signal propagation but can be mitigated by observing the full HF band. These findings demonstrate the potential of HF observations for advancing lightning physics and storm monitoring over long distances.