Wednesday, 14 August 2002: 5:30 PM
Tornado signatures and precursor activity from 3-D lightning mapping observations
Observations have been obtained of the total lightning activity in several
tornadic storms, first in central Oklahoma during the 1998 MEaPRS project
and subsequently in northwestern Kansas and eastern Colorado during STEPS
2000. In each of three or four cases the initial tornado of the storm
(or a funnel cloud that did not extend to ground) was accompanied by a
distinctive lightning-free region, or lightning `hole', in 3-dimensional
observations of the VHF lightning radiation sources. The lightning holes
appear to be associated with the strong updraft on the upshear side of
the storm, and the tornados occurred on the western edge of the holes. The
occurrence of the lightning holes in these and other severe supercell storms
was accompanied by upward moving, high-altitude lightning events indicative
of strong convective surges in the storm. The F1 tornado on June 29, 2000
of STEPS was preceded by a sequence of three such convective surges at 10 to
15 minute intervals extending up to 15-16 km altitude MSL. Each surge was
accompanied by a successively stronger lightning hole, with the third surge
initiating the tornado. The observations appear to be characteristic
of tornadic storms, or of storms having the potential for becoming tornadic,
and could provide an additional means of nowcasting tornado occurrences.
Animations of the overall storm activity show the potential utility of
lightning mapping observations for monitoring storm severity.
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