Characteristics of Negative Leader Propagation Area of Lightning Flashes Initiated in the Stratiform Regions of Mesoscale Convective Systems

To investigate the characteristics of extension areas (mainly the propagation areas of negative leaders in this study), the lightning location data of 254 lightning flashes initiated in the stratiform regions (stratiform lightning flashes) of 14 mesoscale convective systems (MCSs) are analyzed. The results show that most of the flashes have a relatively small lightning area (LA) (≤100 km²), although they are initiated in the stratiform regions. In small or developing MCSs, most negative leaders of stratiform lightning flashes concentrate within the 9–12-km altitude range. In other MCSs with a large-sized and developed stratiform region, besides being in this high-altitude range, the negative leaders are also found to propagate more frequently in a low-altitude range of 5–7 km. Further analysis indicates that most of the stratiform lightning flashes with a large LA (>100 km²) propagate their negative leaders within the high-altitude range, no matter where they are initiated. Moreover, the stratiform lightning flashes with or near the largest LA tend to be initiated 4–6 km below their negative leaders, while most of the stratiform lightning flashes usually propagate their negative leaders horizontally within ±1 km of the first detected very-high-frequency (VHF) radiation source. It is inferred that some in-situ electrifications occurring before and during the formation of the high reflectivity layers in the low-altitude range contribute to these flashes, although the influence of the advection charges from the convective regions still cannot be totally ruled out.