Optical And Electrical Observation And Their Characteristic Analysis Of Continuing Current Of Cloud-to-ground Lightning

The continuing current of cloud-to-ground lightning is a discharge process inwhich charges continuously transfer to ground along the lightning channel after returnstroke. Continuing current is a very important lightning process. In ChinaMeteorological Administration Guangzhou Field Experiment Site for LightningResearch and Testing, many rocket-triggered lightning and natural lightning wereobserved by optical and electrical observation system. Photoelectric character andcharacteristic parameters of continuing current and M component of these lightningobserved were analysed. Also, the relationship between characteristic parameters ofcontinuing current and M component was analysed. The main results and conclusionsare as follows.About rocket-triggered lightning. The current waveforms of Initial ContinuousCurrent (ICC) and Continuing Current (CC) after return strokes were continuous andchanged slowly. Usually, there were current pulses ranging in size superimposed onthese current waveforms. The slow electric field waveforms of ICC and CC wereslowly changing, too. The lightning channel below the cloud was always luminescentduring ICC and CC. The geometric mean of duration is298ms, charge transferred toground is57.2C, action integral is22592A~2s, the mean of current is192A, maximumcurrent during ICC is4.1kA for ICC, while the corresponding values are37ms,7.4C,3303A~2s,202A,1.6kA, respectively, for CC. The geometric mean of mean current ofICC is slightly smaller than that of CC, the duration, charge and action integral of ICCis7~8times of CC.The current waveform, electric field waveform and brightness waveform ofinitial continuous current pulse (ICCP) and M component were approximate symmetry. The geometric mean of current magnitude, charge transferred to ground,half peak width, risetime from10%to90%peak, duration, action integral, currentlevel immediately preceding the ICCP current pulse, interval between successiveICCP is142A,744mC,928μs,441μs,2.88ms,208A~2s,186A and12ms respectivelyfor ICCP, while the corresponding values are308A,753mC,628μs,369μs,1.95ms,342A~2s,243A and7.8ms respectively, for M component. The current waveform of Mcomponent is steeper, narrower and bigger than ICCP; the distribution of Mcomponent is more intensive.There is a correlation between the duration of ICC and half peak width, rise time,duration, magnitude of ICCP, the correlation coefficient are0.77,0.76,0.77and-0.87,respectively. The correlation coefficient of mean current of ICC and magnitude, halfpeak width, duration of ICCP are0.69,-0.61and-0.63, respectively.While the correlation coefficient of duration of CC after return stroke and halfpeak width, rise time, duration, magnitude of M component are0.53,0.49,0.52and-0.79, respectively. The correlation coefficient of mean current of CC and magnitude,half peak width, rise time of M component are0.56,0.52and0.54, respectively.About natural lightning. The duration of CC range from1to358ms, the mean is25ms, the geometric mean is6ms.65percent (20/31) of negative cloud to groundlightning contain continuing current,41percent (42/103) of negative stroke containcontinuing current. The percent of containing continuing current for the last returnstroke (45%) is larger than the first return stroke (32%) in negative lightning.The average value of return stroke current peak initiating a continuing currentwhich lasts longer than10ms is12.4kA, while the corresponding values are29.4kAand35.8kA, for return stroke initiating a continuing current which lasts shorterthan10ms and return stroke which don’t contain continuing current, respectively. Onaverage, the return stroke current peak which contains continuing current is smallerthan the return stroke that don’t, the longer the continuing current, the smaller thereturn stroke current peak.The average detection efficiency of lightning location network is57%fornegative strokes followed by CC (longer than10ms),81%for strokes followed by CC(less than10ms) and87%for strokes that didn’t contain CC.The means of inter-stroke interval just preceding long CC (longer40ms), shortCC (from10ms to40ms) and very-short CC (less than10ms) are23ms,133ms and202ms, respectively. There is an inverse relation between the duration of the inter-stroke interval just preceding the interval containing continuing current and theduration of the continuing current.There is a correlation between the duration of CC and number, duration, intervalof M component, the correlation coefficient is0.52,0.7,0.77and0.94, respectively.