The effects of electric fields on wind driven particulate detachment

Holstein-Rathlou, C.; Merrison, J.P.; Brædstrup, C. F.; Nørnberg, P.

doi:10.1016/j.icarus.2012.04.011

Cited by 19 publications

(14 citation statements)

References 23 publications

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“…In this case the effect of an electric field is to inhibit entrainment and enhance particle aggregation (dielectric attraction). This has been demonstrated experimentally (Holstein-Rathlou et al, 2012;Merrison 2012). A simple model based upon Bagnold's (semiempirical) sand transport model and modifying it with the inclusion of a vertical electric field stress term has successfully reproduced the experimentally observed modification of the threshold and transport rate for saltation in a laboratory sand bed while applying an electric field (Rasmussen et al, 2009).…”

Section: Accepted M Manuscriptmentioning

confidence: 69%

“…Environmental (cooled) wind tunnels have been used occasionally in studies of snow transport, often involving processes of electrification that are relevant to the generation of electrical thunderstorms and lightening (Maeno et al, 1985;Schmidt et al, 1999). In the case of the Aarhus environmental wind tunnel facilities, a fully hermetic, recirculating wind tunnel design has been adopted that allows for control of temperature, pressure, composition, and wind flow and allows for the study of suspended aerosol particles (e.g., dust) (Merrison et al, 2008;Holstein-Rathlou et al, 2012). Because of geometrical constraints this requires compromises to be made with respect to flow speed and uniformity but has been extensively used for wind driven dust and for sand-transport studies.…”

Section: Laboratory Simulatorsmentioning

confidence: 99%

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Laboratory studies of aeolian sediment transport processes on planetary surfaces

2015

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International audienceWe review selected experimental saltation studies performed in laboratory wind tunnels and collision experiments performed in (splash-) laboratory facilities that allow detailed observations between impinging particles on a stationary bed.We also discuss progress in understanding aeolian transport in nonterrestrial environments. Saltation studies in terrestrial wind tunnels can be divided into two groups. The first group comprises studies using a short test bed, typically 1–4m long, and focuses on the transitional behavior near the upwind roughness discontinuity where saltation starts. The other group focuses on studies using long test beds — typically 6 m or more — where the saturated saltation takes place under equilibrium conditions between wind flow and the underlying rough bed. Splash studies using upscaled model experiments allow collision simulations with large spherical particles to be recorded with a high speed video camera. The findings indicate that the number of ejected particles per impact scales linearlywith the impact velocity of the saltating particles. Studies of saturated saltation in several facilities using predominantly Particle Tracking Velocimetry or Laser Doppler Velocimetry indicate that the velocity of the (few) particles having high trajectories increases with increasing friction velocity. However, the speed of the majority of particles that do not reachmuch higher than Bagnold's focal point is virtually independent of Shields parameter—at least for lowor intermediate u⁎-values. In this case mass flux depends on friction velocity squared and not cubed as originally suggested by Bagnold. Over short beds particle velocity shows stronger dependence on friction velocity and profiles of particle velocity deviate from those obtained over long beds. Measurements using horizontally segmented traps give average saltation jump-lengths near 60–70 mm and appear to be only weakly dependent on friction velocity, which is in agreement with some, but not all, older or recent wind tunnel observations. Similarly some measurements performed with uniform sand samples having grain diameters of the order of 0.25–0.40mmindicate that ripple spacing depends on friction velocity in a similar way as particle jump length. The observations are thus in agreementwith a recent ripple model that link the typical jump length to ripple spacing. A possible explanation for contradictory observations in some experiments may be that long observation sequences are required in order to assure that equilibrium exists between ripple geometry and wind flow.Quantitative understanding of saltation characteristics onMars still lacks important elements. Based upon image analysis and numerical predictions, aeolian ripples have been thought to consist of relatively large grains (diameter N 0.6mm) and that saltation occurs at high wind speeds (N26 m/s) involving trajectories that are significantly longer than those on Earth (by a factor of 10–100). However, this is not supported by recent observations from the surf...

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Section: Accepted M Manuscriptmentioning

confidence: 69%

Section: Laboratory Simulatorsmentioning

confidence: 99%

Laboratory studies of aeolian sediment transport processes on planetary surfaces

2015

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“…Here we present evidence that as a feedback, the generated E‐field influences the saltation process itself. Kok and Renno [, , ] and Holstein‐Rathlou et al [] predicted that when the E‐field intensity exceeds a certain threshold, it produces a significant reduction of the static threshold friction velocity necessary for the saltation process to occur. This, in turn, causes a sudden increase in the concentration of saltating particles at a given wind speed (Figure ) [ Kok and Renno , ] and a nonlinear increase of the E‐field around this electric lifting threshold (Figure ) [ Kok and Renno , ].…”

Section: Resultsmentioning

confidence: 99%

The role of the atmospheric electric field in the dust‐lifting process

Esposito

Molinaro

Popa

et al. 2016

Geophysical Research Letters

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Mineral dust particles represent the most abundant component of atmospheric aerosol in terms of dry mass. They play a key role in climate and climate change, so the study of their emission processes is of utmost importance. Measurements of dust emission into the atmosphere are scarce, so that the dust load is generally estimated using models. It is known that the emission process can generate strong atmospheric electric fields. Starting from the data we acquired in the Sahara desert, here, we show for the first time that depending on the relative humidity conditions, electric fields contribute to increase up to a factor of 10 the amount of particles emitted into the atmosphere. This means that electrical forces and humidity are critical quantities in the dust emission process and should be taken into account in climate and circulation models to obtain more realistic estimations of the dust load in the atmosphere.

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“…This work has mainly been based upon the assumption of a conductive sand bed (surface). However, recently it has been experimentally demonstrated that, for the case in which the sand bed is insulating, the application of an electric field in fact significantly increases the threshold shear stress for saltation (Holstein-Rathlou 2012). This is due to dielectric attraction, entirely analogous in its operation to diamagnetic chain formation in the presence of an applied magnetic field.…”

Section: Wind Tunnel Experimentsmentioning

confidence: 99%

Applications of Electrified Dust and Dust Devil Electrodynamics to Martian Atmospheric Electricity

et al. 2016

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Atmospheric transport and suspension of dust frequently brings electrification, which may be substantial. Electric fields of 10 kV m −1 to 100 kV m −1 have been observed at the surface beneath suspended dust in the terrestrial atmosphere, and some electrification has been observed to persist in dust at levels to 5 km, as well as in volcanic plumes. The interaction between individual particles which causes the electrification is incompletely understood, and multiple processes are thought to be acting. A variation in particle charge with particle size, and the effect of gravitational separation explains to, some extent, the charge structures observed in terrestrial dust storms. More extensive flow-based modelling demonstrates that bulk electric fields in excess of 10 kV m −1 can be obtained rapidly (in less than 10 s) from rotating dust systems (dust devils) and that terrestrial breakdown fields can be obtained. Modelled profiles of electrical conductivity in the Martian atmosphere suggest the possibility of dust electrification, and dust devils have been suggested as a mechanism of charge separation able to maintain current flow between one region of the atmosphere and another, through a global circuit. Fundamental new understanding of Martian atmospheric electricity will result from the ExoMars mission, which carries the DREAMS (Dust characterization, Risk Assessment, and Environment Analyser on the Martian Surface)-B R.G. Harrison

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The effects of electric fields on wind driven particulate detachment

Cited by 19 publications

References 23 publications

Laboratory studies of aeolian sediment transport processes on planetary surfaces

Laboratory studies of aeolian sediment transport processes on planetary surfaces

The role of the atmospheric electric field in the dust‐lifting process

Applications of Electrified Dust and Dust Devil Electrodynamics to Martian Atmospheric Electricity

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