Electromagnetic Characteristics of Upward Leader Initiated From the Canton Tower: A Comparison With Rocket‐Triggered Lightning

By using the synchronous observation data obtained at the Tall‐Object Lightning Observatory in Guangzhou (TOLOG) of 2019, the electromagnetic characteristics of upward positive leader (UPL) ascending from the 600‐m high Canton Tower are examined, and are compared with the magnetic field ( B ‐field) radiation of UPL in rocket‐triggered lightning. Before the inception of sustained UPL, small electric field ( E ‐field) pulses are superposed on the fast E ‐field changes. The timescale of B ‐field pulses corresponding to the E ‐field pulses ranges from 5 to 9 μs, and the inter‐pulse interval is about 30 μs, which are both similar to the B ‐field pulses associated with the precursors of rocket‐triggered lightning. Measurements show that the precursor‐like stage is likely common for upward lightning initiated from the Canton Tower. Moreover, the UPL channel of tower‐initiated upward lightning extends significantly in the first several ms with the initial average two‐dimensional (2‐D) velocity of 8.77 × 10 5 m/s (3‐D velocity of 11.0 × 10 5 m/s), which is one order of magnitude faster than the UPL initiated from the wire tip of rocket‐triggered lightning, indicating that initiation of UPL from Canton Tower benefits from a substantial E ‐field enhancement of nearby lightning discharges. However, this favorable condition is rapidly consumed during the UPL development, causing the average 2‐D velocity of UPL to decrease rapidly and maintain at about 0.5 × 10 5 m/s. It is noted that the variation in the 2‐D speed of sustained UPL differs from tower‐initiated upward lightning reported in the literature, which is possibly associated with the physical and geometric properties of the tower.