Particle Image Velocimetry of a Dust Devil Observed in a Desert

Abstract

Dust devils are small-scale atmospheric vortices that are often observed on deserts. Using a video of a dust devil that occurred in a close distance, this study attempts to apply Particle Image Velocimetry (PIV) to obtain flows in the dust devil for the first time. Images taken by two cameras enable us to connect a pixel size into actual length scale. The estimated maximum tangential wind and updraft in the dust devil are 16 m s −1 and 6 m s −1, respectively. These wind speeds are comparable to these of strong ones reported in previous observational studies.(Citation: Ito, J., and H. Niino, 2014: Particle image velocimetry of a dust devil observed in a desert. SOLA, 10, 108−111, doi:10.2151/sola.2014-022.) IntroductionDust devils are atmospheric vertical vortices that often appear on deserts or bare land during daytime in a fine day. Dust particles lifted by strong winds and updrafts in the vortices visualize themselves. Gusty winds associated with them often prevent outdoor activities, and occasionally cause damage to weak structures such as tents and resulting injuries.Several field observations were made to measure winds and pressure depression of dust devils both on the Earth and Mars (e.g Balme and Greeley 2006). In situ observations have used anemometers to measure wind speed in dust devils (e.g Kaimal and Businger 1970). Remote sensing by a Doppler radar (Bluestein et al. 2004) and Doppler lidar (Fujiwara et al. 2011) also measured wind speeds in dust devils and even invisible dust devil-like vortices, respectively.On the other hand, an increasing number of numerical studies have been presented recently. However, most numerical studies suffer from underestimates of wind speeds even if very high resolution is used (e.g. Kanak 2005;Raasch and Franke 2011;Ito et al. 2013). The reason for the underestimate is still uncertain, and further observations of the wind speeds and turbulence characteristics in dust devils are desired.Observations by cameras along with image processing may be a useful method to systematically investigate a number of dust devils. Stanzel et al. (2006Stanzel et al. ( , 2008 have obtained translational speeds of dust devils on the Mars. Balme et al. (2012) implies correlations between translational speeds of dust devils and ambient winds based on terrestrial field observations. Thus, prevailing wind speeds on the Mars may be estimated from a translational motion of a dust devil. These studies, however, did not focus on the flows in dust devils.Particle Image Velocimetry (PIV) is a method which looks for the best matching of distributions of pixel patterns in two successive frames to obtain two-dimensional velocities (e.g. Raffel et al. 1998). In a video of a dust devil (Supplemental movie S1) which is taken by the first author (JI) with consumer cameras, one may perceive its counter-clockwise rotation and upward motions in the vortex. If PIV is applied to the video, some characteristics of the flows in the dust devil may be retrieved. Thanks to the recent progress and widespread ...

Field Measurements of Terrestrial and Martian Dust Devils

“…Measurement of the swirling winds within dust devils has generally been accomplished using in-situ sampling, though particle imaging velocimetry (Ito and Niino 2014) and remote measurements using LIght Detection And Ranging, or "LIDAR" (e.g., Schwiesow et al 1977;Bluestein and Pazmany 2000) have also been employed. Obtaining statistically significant quantities of data is challenging for two main reasons.…”

History and Applications of Dust Devil Studies

“…a waterspout (Fujiwara and Fujiyoshi 2014). Ito and Niino (2014) applied a Particle Image Velocimetry (PIV) method to estimate the wind field in a dust devil which they encountered in Arizona, USA. They estimated the maximum tangential wind in the dust devil as 16 m s −1 .…”