Observations of Pressure Perturbations Within Heat Devils

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Tuesday, 19 January 2010: 5:15 PM
B302 (GWCC)
Steven P. Oncley, NCAR, Boulder, CO; and O. K. Hartogensis

One important variable in vortex dynamics, including that of dust devils, is pressure. However most observations of dust devils have not included pressure measurements due to sensors with too low resolution and/or too slow frequency response. Also, pressure ports have to be carefully designed to remove errors due to the dynamic pressure induced by the port themselves in high winds.

The Advective Horizontal Array of Turbulence Study (AHATS) included 14 quad-disk probe (QDP) pressure ports, each with a high-frequency pressure transducer. A large reservoir provided a common reference pressure for all of the transducers. The ports were placed within two horizontal lines of closely spaced sonic anemometers, where the spacing and heights of these lines were varied four times during the experiment. During the 8 weeks of observations, about 20 devils (we do not have information on whether or not they contained dust) were recorded in which there was a pressure drop of at least 50 Pa for periods on the order of 3 s. With the multiple spatial samples, we can describe the dimensions and shapes of these vortecies. The drops in pressure are generally in cyclostrophic balance with winds measured by the anemometers once the advection velocity is removed.