Characteristics of Upward Lightning on the Beijing 325m Meteorology Tower and Corresponding Thunderstorm Conditions

摘要

abstract_textpComprehensive observation on lightning striking the 325m meteorology tower has been conducted in Beijing, China, during the summer season from 2012 to 2016. For the 20 tower flashes captured by high-speed video camera, 19 (95) cases were initiated from the tower (termed as upward lightning (UL)), with duration of 42-844ms. Most ULs (84.2, 16/19) were triggered by nearby lightning, of which positive cloud-to-ground flashes (+CGs) account for 87.5 (14/16). Analysis on the characteristics of the causal or triggering lightning flashes suggests that the approaching of negative leader process through in-cloud horizontal channel is the vital condition for the initiation of upward leader. Generally, the UL initiation follows the nearby discharges, while for a special case in our data set, the nearby positive return stroke was found to occur after the establishment of an upward channel from the tower. It is worth noting that this +CG led to a significant enhancement of the tower-initiating leader, with eight subsequent return strokes and two M component processes occurring to the tower thereafter. The radar echo of the corresponding thunderstorm indicates that the other-triggered UL (OTUL) tended to occur at the dissipation stage of the thunderstorm with relatively low cloud top height and weak radar echo, while the self-initiating UL (SIUL) was more likely to occur when the thunderstorm was in the mature stage and the tower was underneath the stratiform clouds behind the convective region. The meteorology condition for SIUL involved lower ambient temperature and higher wind speed, as compared to the OTUL./p/abstract_text