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Abstract:

    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 stratiformregion of the
mesoscale convective system. The vertical cross section revealed a relatively low altitude of the
radar echo center, indicative of a lowcharge center of the cloud which was favorable for initiating
tower lightning.