Multiple vortex features in the tornado cyclone and the occurrence of tornado families.

Abstract

Analyses are presented of the tornado tracks for four tornado families affecting Indiana and neighbouring states on 3 April 1974. The study of Agee et al (1975) on the occurrence of multiple suction vortices in the tornado has been used by further extending Ward's (1972) multiple vortex phenomenon to the scale of the tornado cyclone. This has allowed an interpretation of multiple tornado events by means of which consecutive tornado damage paths may be frequently recognized as segmens of cycloidal tracks for multiple vortices occurring within the larger tornado cyclone. A tornado cyclone, most likely within the right rear quadrant of the severe thunderstorm may contain, two, three, or more smaller scale vortices mini tornado cyclones that revolve cyclonically about the centre of the parent tornado cyclone as the entire system translates along with the thunderstorm. It is shown that these centres of action have cycloidal tracks that can be matched with the damage paths of tornado families. Tornadoes are observed to be left-turners or right-turners, depending on what portion along the cycloidal track touchdown and demise occur. A tornado family may be associated with a single vortex parent tornado cyclone which tends to produce longer tornado tracts that do not undergo appreciable turning. Tornado families, however, may be generated by multiple vortex tornado cyclone systems, and in this case tornado tracks follow a curtate cycloid, eventually turning into the cold air and dissipating. Another tornado can reappear, however, as the parent vortex centre returns cyclonically (along the cycloidal path) to more favourable environmental conditions for redevelopmment. Finally, a summary is presented depciting the scales of possible multiple vortex systems associated with the tornado producing thunderstorm. (A)