The Greensburg twister was one of 22 that touched down in southern and central Kansas from the same thunderstorm complex the night of May 4, 2007, and early the next morning.
The Greensburg tornado and a large one northeast of there were so intense the weather service's radar in Dodge City detected vortex holes in them.
A co-author of the study, Mike Umscheid, says radar had never before detected such a thing in a twister. Vortex holes form when winds are rotating so rapidly they pull debris and even large raindrops from the center of the storm.
(Copyright 2008 by The Associated Press. All Rights Reserved.)