摘要:
利用山东一次人工触发闪电的高速摄像和30 m,60 m和480 m的同步电场测量,清晰显示了人工触发闪电上行正先导的传输特征.上行正先导头部光强相对较强,二维发展速度变化波动较大并呈现明显不规则性,表明上行正先导发展具有明显的梯级特征.在先导开始阶段从340 m到705 m高度之间上行正先导平均发展速度为9.8×104m/s.起始速度是3.8×10~4 m/s,局部速度总体上随高度呈现增加趋势.电场变化在近距离产生有规律的梯级状变化,记录到的28个梯级相邻梯级间隔变化从14μs到39μs,几何平均值为25.1μs.估计的先导梯级长度分布在0.9 m到3.7 m,几何平均值为1.7 m.先导电场变化由慢的正向梯级状变化和脉冲变化组成,结合光学和电场变化测量结果.得出正先导头部通道发生弯曲可使其电场变化的梯级特征减弱或消失;正负先导梯级形成机制可能类似,均由其先导头部前端的双向流光发展而来.
Abstract:
Propagating properties of a upward positive leader are analyzed by using the data from the artificially triggered lightning experiment in Shandong 2009,including the high-speed camera records and simultaneous surface electric field fast change measurements at 30 m,60 m and 480 m from the channel.The tip of the leader is brighter,and the leader＇s 2-D partial propagating speed along its channel irregularly changes in a wide range.This indicates that the upward positive leader exhibits obviously stepped characteristics. The average speed is 9.8×10~4 m/s from 340 m to 705 m at the beginning stage of the leader propagating.The upward positive leader is initiated at a speed of 3.8×10~4 m/s.The partial speed shows an increasing tendency with height increasing.The electric field change waveform of upward positive leaders has a regularly stepped shape.The step interval of 28 steps recorded ranges from 14μs to 39μs with a geometrical mean value of 25.1μs.The induced step length varies from 0.9 m to 3.7 m with a geometrical mean value of 1.7m. The electric field change of upward positive leaders includes the slowly stepped change and pulsed change.The high-speed camera records and electric field measurements show that the channel of the leader tip bending can eliminate or weaken the stepped property of the electric field change.The positive step leader has a similar propagating mechanism to that the negative leader has,that is a step of leader originates from a bi-directional streamer front end of the leader tip.
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