Martian dust devil statistics from high-resolution large-eddy simulations (original) (raw)
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Field Measurements of Terrestrial and Martian Dust Devils
Space Science Reviews, 2016
Surface-based measurements of terrestrial and martian dust devils/convective vortices provided from mobile and stationary platforms are discussed. Imaging of terrestrial dust devils has quantified their rotational and vertical wind speeds, translation speeds, dimensions, dust load, and frequency of occurrence. Imaging of martian dust devils has provided translation speeds and constraints on dimension, but only limited vertical constraints on vertical motion within a vortex. The longer mission durations on Mars afforded by long operating robotic landers and rovers have provided statistical quantification of vortex occurrence (time-of-sol, and recently seasonal) that has until recently not been a primary outcome of more temporally limited terrestrial dust devil measurement campaigns. Terrestrial measurement campaigns have included a more extensive range of measured vortex parameters (pressure, wind, morphology, etc.) than have martian opportunities, with electric field and direct measure of abundance not yet obtained on Mars. No martian robotic mission has yet provided contemporaneous high frequency wind and pressure measurements. Comparison of measured terrestrial and martian dust devil characteristics suggests that martian dust devils are larger and possess faster maximum rotational wind speeds, that the absolute magnitude of the pressure deficit within a terrestrial dust devil is an order of magnitude greater than a martian dust devil, and that the time-of-day variation in vortex frequency is similar. Recent terrestrial investigations have demonstrated the presence of
Convective vortices and dust devils detected and characterized by Mars 2020
We characterize the vortex and dust devil activity at Jezero from pressure and winds obtained with the MEDA instrument on Mars 2020 over 415 sols (Ls=6-213º). Vortices are abundant (4.9 vortices per sol with pressure drops >0.5 Pa when correcting from gaps in coverage) and peak at noon. At least one in every 5 vortices carries dust from RDS-MEDA data, and intense vortices are more likely to carry dust. Seasonal variability was small but dust devils were abundant during a dust storm (Ls=152-156º). Vortices are more frequent and intense over terrains with lower thermal inertia favoring a higher daytime surface-to-air temperature gradient. We fit measurements of wind and pressure during dust devil encounters to models of vortices, and investigate their physical characteristics. Diameters range from 5 to 135 m with a mean of 20 m. Three 100-m size events passed within 30 m of the rover. From the close encounters we estimate a dust devil activity of 2.0-3.
Earth, Moon, and Planets, 1997
Although Mars and the Earth share some similarities (for example, axial tilt and rotation rate), they also show marked differences between them. On Mars, the dust raised from the surface into the atmosphere by strong winds absorbs solar radiation and constitutes an important ...
Icarus, 2012
Dust devils – convective vortices made visible by the dust and debris they entrain – are common in arid environments and have been observed on Earth and Mars. Martian dust devils have been identified both in images taken at the surface and in remote sensing observations from orbiting spacecraft. Observations from landing craft and orbiting instruments have allowed the dust devil translational forward motion (ground velocity) to be calculated, but it is unclear how these velocities relate to the local ambient wind conditions, for (i) only model wind speeds are generally available for Mars, and (ii) on Earth only anecdotal evidence exists that compares dust devil ground velocity with ambient wind velocity. If dust devil ground velocity can be reliably correlated to the ambient wind regime, observations of dust devils could provide a proxy for wind speed and direction measurements on Mars. Hence, dust devil ground velocities could be used to probe the circulation of the martian boundary layer and help constrain climate models or assess the safety of future landing sites. We present results from a field study of terrestrial dust devils performed in the southwest USA in which we measured dust devil horizontal velocity as a function of ambient wind velocity. We acquired stereo images of more than a 100 active dust devils and recorded multiple size and position measurements for each dust devil. We used these data to calculate dust devil translational velocity. The dust devils were within a study area bounded by 10 m high meteorology towers such that dust devil speed and direction could be correlated with the local ambient wind speed and direction measurements. Daily (10:00–16:00 local time) and 2-h averaged dust devil ground speeds correlate well with ambient wind speeds averaged over the same period. Unsurprisingly, individual measurements of dust devil ground speed match instantaneous measurements of ambient wind speed more poorly; a 20-min smoothing window applied to the ambient wind speed data improves the correlation. In general, dust devils travel 10–20% faster than ambient wind speed measured at 10 m height, suggesting that their ground speeds are representative of the boundary layer winds a few tens of meters above ground level. Dust devil ground motion direction closely matches the measured ambient wind direction. The link between ambient winds and dust devil ground velocity demonstrated here suggests that a similar one should apply on Mars. Determining the details of the martian relationship between dust devil ground velocity and ambient wind velocity might require new in situ or modelling studies but, if completed successfully, would provide a quantitative means of measuring wind velocities on Mars that would otherwise be impossible to obtain.
Martian dust devils: Laboratory simulations of particle threshold
Journal of Geophysical Research, 2003
1] An apparatus has been fabricated to simulate terrestrial and Martian dust devils. Comparisons of surface pressure profiles through the vortex core generated in the apparatus with both those in natural dust devils on Earth and those inferred for Mars are similar and are consistent with theoretical Rankine vortex models. Experiments to determine particle threshold under Earth ambient atmospheric pressures show that sand (particles > 60 mm in diameter) threshold is analogous to normal boundary-layer shear, in which the rotating winds of the vortex generate surface shear and hence lift. Lowerpressure experiments down to 65mbarfollowthistrendforsand−sizedparticles.However,smallerparticles(i.e.,dust)andallparticlesatverylowpressures(65 mbar follow this trend for sand-sized particles. However, smaller particles (i.e., dust) and all particles at very low pressures (65mbarfollowthistrendforsand−sizedparticles.However,smallerparticles(i.e.,dust)andallparticlesatverylowpressures(10-60 mbar) appear to be subjected to an additional lift function interpreted to result from the strong decrease in atmospheric pressure centered beneath the vortex core. Initial results suggest that the wind speeds required for the entrainment of grains $2 mm in diameter (i.e., Martian dust sizes) are about half those required for entrainment by boundary layer winds on both Earth and Mars.
Icarus, 2012
Dust devils -convective vortices made visible by the dust and debris they entrain -are common in arid environments and have been observed on Earth and Mars. Martian dust devils have been identified both in images taken at the surface and in remote sensing observations from orbiting spacecraft. Observations from landing craft and orbiting instruments have allowed the dust devil translational forward motion (ground velocity) to be calculated, but it is unclear how these velocities relate to the local ambient wind conditions, for (i) only model wind speeds are generally available for Mars, and (ii) on Earth only anecdotal evidence exists that compares dust devil ground velocity with ambient wind velocity. If dust devil ground velocity can be reliably correlated to the ambient wind regime, observations of dust devils could provide a proxy for wind speed and direction measurements on Mars. Hence, dust devil ground velocities could be used to probe the circulation of the martian boundary layer and help constrain climate models or assess the safety of future landing sites.
Three-dimensional numerical simulation of Martian global dust storms
Journal of Geophysical Research, 1995
We present results from the first numerical simulations of simultaneously evolving three-dimensional thermal, dynamical, and radiatively active suspended dust fields in the Martian atmosphere. Simulations of southern summer dust storms (arising from a prescribed southern subtropical surface dust source) conducted with a Mars general circulation model (GCM) illustrate the important role of dust transport by atmospheric eddies. Both traveling and stationary eddies contribute to dust transport to high latitudes in both hemispheres. These hemispheric differences arise from seasonal and topographic effects. Transport into the south polar regions is accomplished primarily by thermally and topographically forced standing eddies. Both traveling and stationary eddies transport dust to middle and high northern (winter) latitudes. Atmospheric wave motions are affected by the developing storms. Thermal tidal amplitudes increase at storm onset, with the calculated pressure response at a model grid point corresponding to the location of the Viking Lander 1 site in good agreement with observations. In qualitative agreement with observations, winter hemisphere baroclinic waves weaken during the early stages of the storm, but as the storm wanes, amplitudes of these waves increase. A slowly westward propagating (9 degrees of longitude per sol) zonal wavenumber one feature in the temperature and geopotential fields at middle northern latitudes amplifies rapidly during the initial sols (Martian solar days) of the simulated storms. This feature is suggestive of the observed north polar warming which occurred during the 1977B global dust storm, but the simulations produce a much weaker polar waxming (--10 K at 0.5 mbar) than was observed (40-50 K). The globally integrated CO2 condensation rate decreases by 15-20% during the simulated dust storm onset and would likely be decreased more if a stronger polar waxming were produced. During the initial stages of the simulated storms, surface stress values in the southern subtropics intensify due primarily to the intensification of the Hadley circulation and thermally driven fides. This supports the hypothesis that these components of the general circulation contribute strong positive feedbacks to the developing storms. Paper number 95JE02984. 0148-0227/95/95JE-02894505.00 thermodynamic state of the atmosphere evolve simultaneously and interactively. In the simulations discussed herein, the magnitude, spatial extent, and duration of the surface dust source are prescribed. Previous numerical simulations of dust storm conditions on Mars have either used interactive two-dimensional models (Haberle et al. [1982], hereafter HI; Murphy et al. [1993], hereafter M1) or have been GCM simulations with prescribed fixed distributions of radiatively active dust [Moriyama and lwashima, 1980; Pollack et al., 1990, 1993; Haberle et al., 1993; Barnes et al., 1993; Greeley et al., 1993]. Both types of models showed that there is very strong feedback between absorption of solar radiation by dust and the general circulation. These and other studies [Conrath, 1975; Murphy et al., 1990a] illustrate the strong dependence of the zonally symmetric circulation structure upon suspended dust load and demonstrate the importance of particle size and shape for dust removal and transport. Two-dimensional models are unable, however, to represent longitudinally asymmetric features such as diurnal variations and transient and stationary planetary waves. These are known to be major components of the general circulation (see Zurek et al., [1992] for a review of the Martian general circulation). Previous GCM simulations include these longitudinally asynunetric features, but they preclude study of dust transport and transient phenomena when the dust distribution and the general circulation evolve 26,357 26,358 MURPHY ET AL.: SIMULATIONS OF MARTIAN GLOBAL DUST STORMS together. Some three-dimensional simulations have also shown how fixed, prescribed atmospheric dust load can impact such atmosphere/surface interactions as surface stress [Greeley et al., 1993] and CO 2 condensation/sublimation [Pollack et al., 1990]. Because CO 2 is the major atmospheric constituent, the latter process is directly coupled to the annual cycle of surface pressure . The transient evolution of surface stress and CO 2 condensation/sublimation can be studied with a coupled dust transport general circulation model. In this investigation, great dust storm onset is simulated with a prescribed surface dust source confined within a specified southern subtropical latitude band. The source is maintained for 10 Martian days (sols) and then turned off, with the circulation and dust distribution continuing to evolve for 40 additional sols. This experiment is compared with a control run for the same season without a dust source, and we shall also briefly refer to preliminary results from runs with the same dust source but without topography, with a different dust source strength, and with the dust source confined in longitude as well as latitude.