Observed Effect of Mesoscale Vertical Vorticity on Rotation Sense of Dust Devil-Like Vortices in an Urban Area

Abstract

Dust devil-like vortices were detected by a three-dimensional scanning coherent Doppler lidar (3D-CDL) in an urban area of Sapporo, Japan, from April 2005 to July 2007. A total of 57 strong, dust devil-like vortices with vertical vorticity exceeding 0.1 s^-1 were detected in 8 days of the observation period and were associated with a convective cell (fish net) pattern of wind fields detected by the 3D-CDL. The observed vortices had both rotation senses for 7 days. However, all of 7 dust devil-like vortices were cyclonic on 4 October 2006 when cyclonic mesoscale circulation with 4.5 × 10^-4 s^-1 in vertical vorticity existed over the 3D-CDL observation area. This result is the observed evidence that mesoscale circulation affects rotation sense of vortices.