Characteristics of upward lightning from a 325-m-tall meteorology tower

Comprehensive observations of lightning flashes striking at a 325-m-tall meteorology tower were conducted in Beijing, China, during the summer of 2012. The images from high speed camera and normal video camera and the measurements of electric field changes were examined to investigate the characteristics of upward negative lightning initiated from the tower. Among eight upward lightning flashes documented during two thunderstorms, four were self-initiated events without lightning activity nearby prior to their initiation, two were triggered by the nearby positive cloud-to-ground lightning (+ CG) with the initiation of the upward leaders from the tower lagged 0.4 ms and 5 ms behind, respectively, and the remaining two were triggered by nearby intra-cloud lightning activities. The average 2-D speed of the upward positive leader was 1.0 × 105 m/s within several hundred meters above the tower tip. When the upward lightning occurred, the tower was swept by a radar echo zone with not very strong peak intensity of about 35-45 dBZ, which exhibited as a secondary convective area in the trailing stratiform region of the mesoscale convective system. The vertical cross section revealed a relatively low altitude of the radar echo center, indicative of a low charge center of the cloud which was favorable for initiating tower lightning.