Pressure at the ground in a large tornado

A number of instruments were placed on the ground across the path of a larg e tornado that passed west of the town of Allison, Texas, on June 8, 1995. The center of the tornado came within 660 m of the closest instrument, whic h recorded a pressure drop of 55 mbar and a subsequent pressure rise of 60 mbar. During the lowest recorded pressures (near r = 660 m), there were lar ge and rapid pressure fluctuations; the largest fluctuation was a 10-mbar s pike lasting 2 s. A second instrument on the opposite side of the tornado r ecorded a pressure drop of 26 mbar. From the pressure variations with time P(t) at the two instruments, the variation of pressure with distance p(r) f rom the center of the tornado has been deduced for r > 660 m. As r decrease s, the measured pressure function p(r) drops more abruptly than would be ex pected from conservation of angular momentum of air spiraling inward near t he ground level.