date: 2012 June 20 (Wed) 15:00-16:00
room: CPS Conference Room
speaker: Junshi Ito (The University of Tokyo)
organizer: Yoshiyuki O. Takahashi
title: Formation mechanism of simulated dust devils
abstract: Dust devils are small scale vertical vortices and often seen on the desert in fine weather conditions. Dust devil-like vortices occur even in idealized horizontally uniform simulated convective mixed layers. Thus, formation of dust devils appear to be a universal in the convective mixed layers.
In this study, we investigate the formation mechanism of the simulated dust devil-like vortices. To observe vorticity budget in the vortices is too complecated in the highly turbulent convective mixed layers where dust devils occur. Instead, our analysis employs the circulation which is defined as the surface integral of vorticity on a material surface. A material surface is placed across a simulated dust devil, and its deformation is tracked with multiple backward-trajectories. The material surface is converged into the dust devil from a wide horizontal area neat the surface with approximately conserving the circulation. A statistical study shows that the convective mixed layers are inherently accompanied by a circulation which is sufficient to form dust devils.
keywords: planetary atmosphere, Earth, dust devil, turbulence, convection