Inferences on upward leader characteristics from measured currents

We analyzed in detail currents associated with upward unconnected leaders (UULs) initiated from the Kennedy Space Center (KSC) Industrial Area Tower (IAT). Current measurements of UULs natural lightning are relatively rare and provide important insights into development propagation leaders. Eight were KSC-IAT between August 1, 2018 November 15, 2019. All positive as they occurred response to downward negative that attached ground near tower. The KSC Mesoscale Eastern Range Lightning Information System (MERLIN) located these nearby strokes at distances ranging 185 783 m tower, median being 538 m. peak current for ranged 13 69.3 kA, 26.7 kA. From perspective charge transferred, can be considered a bipolar phenomenon; transferred inception their current-polarity reversal, following which, effectively ground. labeled former time-period UUL phase latter collapse phase. duration 789 μs − 6.4 mC, respectively, 388 4.7 respectively. Overall, net by was negative. During phase, UUL-currents consisted faster (total durations order 10 μs) impulses overlaid on slower (millisecond-scale) “background” current. background-to-peak current-pulse amplitudes 3.4–289.2 A 30.1 A. pulse total full-width half-maximum (FWHM) 14.1 4.9 μs, 10-to-90% risetimes 3.2 2.0 Interpulse intervals 4.2–132.8 20 μs. Generally speaking, larger, background higher, interpulse shorter later times during UULs. It is likely higher more closely approached leader branch versus lower-current