Abstract: Lightning presents substantial hazards to urban infrastructure and public safety, particularly in densely populated coastal regions with frequent thunderstorm activity. Since 2016, a long-term natural lightning observation campaign has been jointly conducted by Shenzhen National Climate Observatory and Lightning Physics Research Team of the Hong Kong Polytechnic University at 356-meter-tall Shenzhen Meteorological Gradient Tower (SZMGT), a subtropical coastal monitoring facility in southern China. A comprehensive statistical analysis of lightning current waveforms recorded between 2017 and 2023 at SZMGT is presented, focusing on return stroke parameters and early-stage discharge activity.
The dataset comprises 89 lightning events, including 38 with complete current records. These records consist of 26 first return strokes and 19 subsequent strokes, all exhibiting negative polarity. Quantitative analysis is performed on four key parameters: Peak current, transferred charge, specific energy, and maximum current rate of change. The median peak current reaches 61 kA for first strokes and 32 kA for subsequent strokes, approximately twice the value reported in previous studies. The ratio between 95th and 5th percentiles exceeds 13 for both stroke types, reflecting a broad distribution. The median transferred charge and specific energy are 4.1 C and 8.1×10⁴ A²s for first strokes, and 1.8 C and 1.1×10⁴ A²s for subsequent strokes, respectively. Median values of maximum current derivatives, filtered at 2 MHz to eliminate high-frequency oscillations, are 35 kA·μs^-1 and 71 kA·μs^-1 for first and subsequent strokes, respectively. These are also nearly double those values previously reported.
During 2019-2020, the implementation of a shock-tolerant low-noise amplifier facilitated the detection of precursor corona discharge activity, with measurable currents ranging from tens of milliamperes to several amperes occurring up to 372 ms prior to upward leader initiation. This constitutes rare evidence of pre-discharge activity on tall structures. Furthermore, synchronized current and high-speed optical data were acquired for 24 events, enabling detailed correlation analysis between current evolution and corresponding optical radiation.
Despite these advancements, several technical challenges persist. Asynchronous triggering among subsystems restricts complete data acquisition, and electromagnetic interference in the tower vicinity frequently compromises isolated power and signal units. Furthermore, operational limitations have emerged due to the amplifier’s decommissioning following power supply degradation, impeding continued investigations of lightning initiation.
In conclusion, SZMGT campaign provides unique empirical insights into lightning in coastal megacities. Future research efforts should prioritize system enhancements, particularly in measurement synchronization, electromagnetic shielding, and advanced sensors deployment, to enable more comprehensive characterization of lightning processes.