MESOANALYSIS OF THE ILLINOIS TORNADOES OF 9 APRIL 1953

Abstract

The original radar film of the Illinois tornadoes was analyzed with the additional use of surface observations from the available stations in the vicinity. This study shows that the tornadoes were associated with a tornado cyclone resembling a miniature hurricane in many respects. The tornado cyclone was only 30 mi in diameter, and it was characterized by an eye at its center, spiral echo bands, etc. The echo movement inside the tornado cyclone indicates that air converged at low levels then rose following the boundary of the eye. The location of the Champaign tornado with respect to the tornado cyclone center was carefully examined; it was placed beneath the ring of maximum wind, south of the cyclone center. Such a relative position was maintained at least during the developing stage of the tornado. It was also found that the direction of movement of the tornado cyclone formed a 25 deg angle with that of the echoes in outer fields.