Coordinated Observation Of Sprite + Halo And Lightning Electric Field Simulation

Based on the concurrent measurement of broadband magnetic sferics,we examined the high-speed video images of two sprites with diffuse halo feature that were produced by positive cloud-to-ground(CG)strokes over a mesoscale convective system(MCS)in central United States to investigate the temporal and spatial connection between halo,sprite and parent lightning strokes.In addition,this paper calculates the electromagnetic field of return stroke at the height of halos using a transmission line(TL)model having as a input parameter various lightning stroke base currents measured during Shandong Artificial Triggering Lightning Experiment(SHATLE)and simulated currents to examine the individual components(i.e.,electrostatic,induction,and radiation)of electric field(E-field)perturbation.Combined observation and numerical simulation analysis,(1)halos produced by positive strokes observed are accompanied by visible streamer development,which is mainly attributed to the relatively long timescale of charge transfer in the causative strokes.It is speculated that in addition to the electrostatic field,the induction field(with amplitude more than half of the total E-field)is the main component of the total Efield within the first 0.56+0.13 ms directly above the lightning channel at 80 km.(2)Due to the time delay of propagation and ionospheric reflection of electromagnetic field,At an altitude above 80 km,although the amplitude of the induction field is gradually reduced,the double peaks are close to each other,so that the peak value is a relatively increasing process.Thus,the amplitude of the induction field is attenuated slower than the electrostatic field at altitudes above 80 km.In other words,the role of the induction field is more pronounced at the height of elves,validating the conclusions of Lu(2006).(3)Compared to the peak value of the input pulse current,its time scale has a greater influence on the illumination time of the sprite event.When the time scale of the current is longer,the corresponding induction field and electrostatic field component are also larger,which promotes the development of the vertical structure of the sprite;the long-term lightning continuous current can maintain a high electric field in a region,so that the existing sprite continue to illuminate;the long-delay sprite is a phenomenon that occurs under the combined effect of ambient conductivity,an existing electric field,and a transient increase in the long continuous current of CG(due to the presence of the M component or the second flash).(4)The M-component,the longer time rising edge,the wavy long tail of base current,and the increase of the base current time scale can increase the amplitude of electrostatic and induction field at the height of halos,and drive the occurrence of halos and the possible subsequent development of streamers,therefore forming sprites.The results above enrich the understanding on the mechanism of halo production and the lightning-induced electromagnetic field in the middle and high-altitude atmosphere.It also paves the way for future accurate modeling and artificial initiation of halos.