Field Measurements of Terrestrial and Martian Dust Devils

Abstract

OATAO is an open access repository that collects the work of Toulouse researchers and makes it freely available over the web where possible. This is an author-deposited version published in: http://oatao.univ-toulouse.fr/ Eprints ID: 17289

Large-Eddy Simulations of Dust Devils and Convective Vortices

“…In the sensitivity experiment of Ito et al (2010b), the strong vorticity extrema corresponding to convective vortices -and thus possible dust devils -are more frequent when both the background wind is weaker (as is also found by Ohno and Takemi, 2010b) and sensible heat flux is stronger. Those findings are consistent with observations (see Murphy et al (2016) and Rafkin et al (2016) in this issue). Ito et al (2010b) compared experiments with nearly calm environmental wind (0.5 m s −1 ) and those with much stronger winds (5 − 15 m s −1 ).…”

“…The importance of convective tilting of horizontal vorticity in dust devil formation is demonstrated by simulations that show vortices forming within convergent branches of convective cells (and not only at cell vertices). The convective vortices modeled in LES agree well with field measurements (see Murphy et al (2016) in this issue), showing similar velocity structure and diurnal behavior as actual dust devils (Table 1). However, some differences from observations were noted in the vortex intensity in terms of the central pressure deficit, where the simulated vortices are weaker than the observations: Kanak (2005) found that the central pressure drop deviated from measured values in Sinclair (1973) by nearly a factor of 5.…”

“…Ohno and Takemi (2010b) investigated the effects of background wind speed on the generation of vortices and found that vortices are generated most preferably in medium-wind conditions in terms of their number, intensity, and lifetime. Ohno and Takemi (2010b) also indicated that a stability condition controls the generation of dust devils, as was identified by Takemi (2008) and from field observations (see Murphy et al (2016) in this issue).…”

“…In LES, the equations of motion for the atmospheric fluid are integrated on a gridded mesh with a typical spacing of tens of meters or less in order to resolve the larger turbulent eddies that are responsible for most of the energy transport within the CBL. Thus, LES are capable of resolving dust devils, which have diameters smaller than 1 km (see Murphy et al (2016), Fenton et al (2016), and Lorenz and Jackson (2016) in this issue), in contrast to simulations carried out by either Global Climate Models (GCM, in which mesh spacing is a couple hundreds of kilometers) or Regional Climate Models (RCM, in which mesh spacing is typically several kilometers) ( Figure 1). Furthermore, in LES, convective vortices possibly leading to dust devils are explicitly resolved.…”

“…LES have been instrumental in broadening the knowledge of the properties, evolution, and statistics of dust devils. The LES modeling approach is highly complementary to measurements (see Murphy et al (2016) and Fenton et al (2016) in this issue) to study dust devils, since all properties of modeled vortices (wind speed, temperature, pressure, stability), as well as local environmental conditions, are accessible with LES.…”