资源环境科技发展态势分析平台

The beginning of all 75 lightning flashes in two small thunderstorms was investigated using an array of electric field change (E-change) meters and an array of VHF sensors with the goal of determining if an initial E-change (IEC) preceded the initial breakdown (IB) pulses in each flash. IECs were found at the beginning of all 62 flashes in Storm 1 and all 13 flashes in Storm 2. Hence, it is concluded that an IEC is a fundamental part of most or all lightning initiations and that an IEC is needed prior to the first IB pulse in a flash. IEC durations averaged 0.23ms for cloud-to-ground (CG) flashes (range 0.08-0.54ms) and averaged 2.7ms for normal intracloud (IC) flashes (range 0.04-9.8ms). IEC point dipole moments averaged 26Cm for CG flashes (range 4-86Cm) and averaged -140Cm for normal IC flashes (range -8 to -650Cm). IEC current moments averaged 120kAm for CG flashes (range 41-410kAm) and averaged -91kAm for normal IC flashes (range -2 to -630kAm). E-change data support the suggestion that weak narrow bipolar event type events initiate some lightning flashes, but 41 of the 75 flashes had no detectable initiating pulse >0.04Vm(-1) range normalized to 100km. Two flashes had two IECs; the second IEC of each flash initiated a new lightning channel that propagated in a new direction and at a higher altitude than the original development after the first IEC.