Pressure measurements at the ground in an F-4 tornado

Aerodynamically-designed probes were deployed directly in the path of an F-4 tornado near Manchester, South Dakota, on June 24th, 2003. These autonomous probes performed in-situ ground-level measurements of the free-field static pressure, temperature, and relative humidity as the tornado passed directly over the probes. A sharp pressure drop lasting about 40 seconds was observed. Of particular interest was the maximum recorded pressure drop of about 100 mbar, as well as several smaller fluctuations of notable amplitude. This paper describes the measurements made during this event and discusses the significance of the results in terms of the dynamic structure of the tornado.