Characteristics of Lightning Flashes Associated With the Charge Layer Near the 0 °C Isotherm in the Stratiform Region of Mesoscale onvective Systems

Abstract

Data from an S‐band Doppler radar system and a three‐dimensional very high frequency (VHF) radiation source location system in Chongqing, China, were combined to analyze the characteristics of stratiform lightning flashes associated with the charge layer near the 0 °C isotherm (SL0s) in 10 mesoscale convective systems during the summers of 2014–2015. Most of the SL0 events occurred during the dissipating stage of two thunderstorms. The bright band was found to have a very close relationship with the initiation of the SL0 events. The noninductive and inductive charging mechanisms associated with the process of melting ice particles were inferred to contribute to the charge of the bright band area. The reflectivity at the first located VHF radiation source (FirstS) of the SL0s was always weaker than that in the reflectivity core within the lightning area. The stronger the reflectivity core, the greater the difference between the reflectivity and the reflectivity core. The SL0s generated by the thunderstorms with low SL0 frequency tended to have weaker reflectivity at the FirstS but a stronger reflectivity core in the lightning area than that of the thunderstorms with high SL0 frequency. In the storms with low SL0 frequency, SL0s occurred only when the initiation height of the stratiform lightning flashes decreased gradually toward the height range of the SL0s; but in one storm with high SL0 frequency, the SL0s were generated simultaneously with the stratiform lightning flashes initiated at a high level. It gives a clue that the melting charging mechanisms may enhance the charge density of the bright band area.

Fine Three‐Dimensional VHF Lightning Mapping Using Waveform Cross‐Correlation TOA Method

“…Furthermore, the detected pulse peaks for every 80 μs were saved and transferred to the center station via the Internet and the real‐time 3‐D lightning map obtained by the parameter TOA method could be monitored at the center station. The TOA method used at the central station was developed by Liu et al () and Wang et al () and was similar to that described by the LMA (Koshak et al, ). A detailed description of the system can be found in Liu et al ().…”

Radar Reflectivity of Lightning Flashes in Stratiform Regions of Mesoscale Convective Systems

“…The data for 14 MCSs in Chongqing, China, were used to analyze the altitude and reflectivity distributions of stratiform lightning flashes. The data were obtained from observations during the summer months of 2014-2015 using the observational equipment of Wang et al (2018). 2.1.1.…”

“…2.1.1. VHF Radiation Source Location Network VHF source data were obtained from a VHF radiation source location network of 14 sensors in Chongqing (Wang et al, 2018). The maximum and minimum distances between two sensors were 100 and 10 km, respectively.…”

“…The location errors in the altitude of the VHF radiation source were <200 m. The trigger threshold of most of the sensors had to be set to a high level to reduce electromagnetic interference from the Chongqing urban area. This means that the network mainly detects VHF radiation sources with a strong power (Wang et al, 2018). The threshold of chi-square (χ 2 ) was set to 50, although the values of χ 2 in the calculation were mostly ≤5.…”

“…For some thunderstorms occurred on 7 August 2015 (storm 6 and 7), the main bodies of these storms, which had a larger scale than the observation domain (e.g., Figure 6b in Wang et al, 2018), just passed through the observation domain. This caused that most of the stratiform lightning flashes could be captured by the observation domain and the frequency of stratiform lightning flashes in these storms were evidently higher than that in others although the total number of the stratiform lightning flashes may be still underestimated (e.g., Figure 6b in Wang et al, 2018). Therefore, the frequency of stratiform lightning flashes in the observation domain were not fully be capable of characterizing the strength of thunderstorms.…”