RELATIONSHIP AMONG TORNADOES, VORTICITY ACCELERATION, AND AIR MASS STABILITY

Abstract

Numerical computations of the local change with respect to time of the local tendency of the vertical component of the vorticity of the surface wind and a stability index were made at 3-hour intervals for fifteen tornado days during the period from February to June 1961. Average values of these two parameters were computed with reference to tornado occurrences at the center of the computation grid. These average values are shown for five time periods: 9 to 12 hr., 6 to 9 hr., 3 to 6 hr., 0 to 3 hr. prior to tornado occurrences, and 0 to 3 hr. after tornado occurrences. It appears the tornadoes develop within an area under the influence of increasing cyclonic vorticity tendency and characterized by a conditionally unstable air mass. These conditions apparently exist during a short time interval before tornado occurrence, with tornadoes developing only after their combined intensity reaches a critical value.