Abstract
We investigate the characteristics of a dust-devil-like vortex (DDLV) observed using thermal image velocimetry (TIV) at a sports ground in Tokyo. Thermal image velocimetry provides unique observations of the two-dimensional velocity distribution for a DDLV with high spatio–temporal resolution (i.e., tens of cm s−1) near the ground. Two DDLVs were detected, one each in summer and winter, and the quantitative features of the larger, stronger DDLV in the winter are examined. The size and strength of the detected DDLV, which are quantified using TIV, are within the ranges reported in past observations and numerical simulations of dust devils. The vortex appears at the boundary of a cold-air current near a 55-m building wall, and persists for more than 3 min.
Highlights
Dust devils are thermally-induced vertical vortices comprising sediments that are picked up from the ground
We examined thermal image velocimetry (TIV) flow and velocity outputs and applied them to our dust-devil-like vortex (DDLV) analysis
Visual inspection of the processed images revealed that the swirling motion was observed for more than 3 min before the thermal infrared (TIR) camera stopped recording, the swirl had a diameter of about 30 m, and the swirl rotated in an anticlockwise direction
Summary
Dust devils are thermally-induced vertical vortices comprising sediments that are picked up from the ground. Fujiwara et al (2011) observed many dust-devil-like vortices (DDLVs) in an urban area using Doppler lidar. Some researchers have considered the initiation of dust devils and DDLVs to be associated with vertical airflow shear near the ground, due to opposing warm and cold airflow lifting a horizontal vortex tube near the surface (e.g., Renno et al 2004). They are associated with multi-directional convergent flows on the ground below convective cells (Raasch and Franke 2011). Use of Thermal Image Velocimetry to Measure a Dust-Devil-Like Vortex
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