Pressure at the ground in a large tornado

A number of instruments were placed on the ground across the path of a large 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, which 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 large and rapid pressure fluctuations; the largest fluctuation was a 10-mbar spike lasting 2 s. A second instrument on the opposite side of the tornado recorded 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) from the center of the tornado has been deduced for r>660 m. As r decreases, the measured pressure function p(r) drops more abruptly than would be expected from conservation of angular momentum of air spiraling inward near the ground level.