摘要
Using2high-speedcameras,wehaverecorded14negativecloud-to-ground(CG)lightningflashes,halfofwhicharenaturalandtheothersareartificiallytriggered.Thetwo-dimensional(2D)propagationspeedofdifferenttypeleadersandtheluminosityoflightningchannelareanalyzedindetail.Bidirectionalleaderprocessesareobservedduringtheinitialprocessesoftwoaltitudetriggerednegativelightning(ATNL)flashes.Theanalysisshows:thepropagationspeedoftheupwardpositiveleader(UPL)beforetheinitiationofthedownwardnegativeleader(DNL)isattheorderof10~4-10~5ms~(-1);theUPLcanbeintensifiedbytheinitiationanddevelopmentoftheDNLinthewaythattheluminosityisenhancedandthespeedisspedup;afterinitiation,theDNLinoneATNLflashpropagatesdownwardthreetimesintermittentlywithintervalofabout1ms,whilethatintheotherATNLflashpropagatesdownwardcontinuouslywithaspeedattheorderof10~5ms~(-1).Inthefiveclassicaltriggerednegativelightning(CTNL)flashes,thepropagationspeedsoftheUPLsvarybetween0.35×10~5and7.71×10~5ms~(-1),andthevariationsoftheirluminositiesandspeedsarequitecomplexduringthedevelopmentprocesses.Amongthefourobservednaturalnegativelightningflashesoccurredontheland,threehaveonlyonereturnstoke(RS)eachandalloftheirDNLshavemanybrancheswithanaveragespeedattheorderof10~5ms~(-1);whiletheanotheronehas13RSs.IntheCGflashwith13RSs,theDNLbeforethefirstRShasnoobviousbranchbelow1.4kmabovetheground,anditsspeedrangesfrom2.2×10~5to2.3×10~6ms~(-1)betweentheheightsof0.7and1.4kmandexceeds3.9×10~6ms~(-1)below0.7km;precedingthe4thRS,anattemptedleaderisobservedwithaspeedrangingfrom1.1×10~5to1.1×10~6ms~(-1)between0.8and1.5km.Asforthethreeobservednaturalnegativelightningflashesoccurredonthesea,eachhasonlyoneRS,andeachDNLprecedingtheRShasafewbranches,twoofwhichhaveanaveragepropagationspeedat
出版日期
2008年01月11日（中国期刊网平台首次上网日期，不代表论文的发表时间）
