Figure 1: Frequency versus time spectrum showing the Trans-Ionospheric Pulse Pair
detected by the Blackbeard receiver on Alexis at 0627:13.197 on July 3, 1995
while at an altitude of 752 km over the central U.S. at 90.66
W and
35.72 N. The duration of this frame is 85 microseconds. The receiver was
in its high band mode covering frequencies of 100-166 MHz at this time.
Figure 2: The geometry of the near simultaneous detection of the cloud stroke
associated with the TIPPs shown in Figure
1. Sources along the curved
isochrons (0.75 
0.05 ms) would arrive with the delay observed. The two
circular bands, consisting of dotted concentric circles surrounding a solid
circle, show the line-of-sight horizon for sources occurring at altitudes
from 8 to 12 km. Stations C8, F4 and ED did not detect any pulses at the time
of the TIPP. Their 10 km horizons are shown as light gray circles. The Alexis
subsatellite point is also shown.
Figure 3: The locations of cloud-ground strokes for the 10 minute interval
centered on the TIPP shown in Figure
1. The locations of these strokes were
triangulated by the NLDN from their nationwide array of detectors. The isochron
of Figure 2 is indicated for reference.