The Experts below are selected from a list of 324 Experts worldwide ranked by ideXlab platform
Ralph D. Lorenz - One of the best experts on this subject based on the ideXlab platform.
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a timelapse camera dataset and markov model of Dust Devil activity at eldorado playa nevada usa
Aeolian Research, 2018Co-Authors: Ralph D. Lorenz, Brian Jackson, Peter D LanaganAbstract:Abstract We report a May-June 2015 survey of Dust Devil activity on a Nevada desert playa using an inexpensive digital timelapse camera. We discuss techniques for exploiting the large volume of data (∼32,700 images, made publicly-available) generated in these observations, similar to imaging from Mars landers and rovers, noting the diurnal image filesize variations as a useful quick-look metric of weather conditions. We present results from a semi-automated image classification: this classification is available to other workers, for example for benchmarking automated procedures. The acquisition of images at 1/min for some 36 days permits study of the diurnal variation of Dust Devil activity (e.g. 85% of the Dust Devil images [i.e. those images manually classified as showing Dust Devils] occur between 12:00 and 17:00; during the period of peak activity 13:00–15:00 about 7% of images contain well-defined Dust Devils of several meters diameter or larger). The data also permit the dependence of Dust Devil characteristics on ambient conditions. We construct a simple two-state Markov model for the occurrence and persistence of Dust Devils (a few per cent chance that new Dust Devil activity appears in the next image; and a ∼45% chance that activity stops) which may help inform strategies for acquiring and interpreting field observations.
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A framework for relating the structures and recovery statistics in pressure time-series surveys for Dust Devils
Icarus, 2018Co-Authors: Brian Jackson, Ralph D. Lorenz, Karan DavisAbstract:Abstract Dust Devils are likely the dominant source of Dust for the martian atmosphere, but the amount and frequency of Dust-lifting depend on the statistical distribution of Dust Devil parameters. Dust Devils exhibit pressure perturbations and, if they pass near a barometric sensor, they may register as a discernible dip in a pressure time-series. Leveraging this fact, several surveys using barometric sensors on landed spacecraft have revealed Dust Devil structures and occurrence rates. However powerful they are, though, such surveys suffer from non-trivial biases that skew the inferred Dust Devil properties. For example, such surveys are most sensitive to Dust Devils with the widest and deepest pressure profiles, but the recovered profiles will be distorted, broader and shallow than the actual profiles. In addition, such surveys often do not provide wind speed measurements alongside the pressure time series, and so the durations of the Dust Devil signals in the time series cannot be directly converted to profile widths. Fortunately, simple statistical and geometric considerations can de-bias these surveys, allowing conversion of the duration of Dust Devil signals into physical widths, given only a distribution of likely translation velocities, and the recovery of the underlying distributions of physical parameters. In this study, we develop a scheme for de-biasing such surveys. Applying our model to an in-situ survey using data from the Phoenix lander suggests a larger Dust flux and a Dust Devil occurrence rate about ten times larger than previously inferred. Comparing our results to Dust Devil track surveys suggests only about one in five low-pressure cells lifts sufficient Dust to leave a visible track.
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Dust Devil Sediment Transport: From Lab to Field to Global Impact
Space Science Reviews, 2016Co-Authors: Martina Klose, Mark T. Lemmon, Ralph D. Lorenz, Stephen R. Lewis, Lynn D V Neakrase, Bradley C. Jemmett-smith, Henrik Kahanpää, Melinda Kahre, Peter Knippertz, Claire NewmanAbstract:The impact of Dust aerosols on the climate and environment of Earth and Mars is complex and forms a major area of research. A difficulty arises in estimating the contribution of small-scale Dust Devils to the total Dust aerosol. This difficulty is due to uncertainties in the amount of Dust lifted by individual Dust Devils, the frequency of Dust Devil occurrence, and the lack of statistical generality of individual experiments and observations. In this paper, we review results of observational, laboratory, and modeling studies and provide an overview of Dust Devil Dust transport on various spatio-temporal scales as obtained with the different research approaches. Methods used for the investigation of Dust Devils on Earth and Mars vary. For example, while the use of imagery for the investigation of Dust Devil occurrence frequency is common practice for Mars, this is less so the case for Earth. Modeling approaches for Earth and Mars are similar in that they are based on the same underlying theory, but they are applied in different ways. Insights into the benefits and limitations of each approach suggest potential future research focuses, which can further reduce the uncertainty associated with Dust Devil Dust entrainment. The potential impacts of Dust Devils on the climates of Earth and Mars are discussed on the basis of the presented research results.
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Dust Devil Steady-State Structure from a Fluid Dynamics Perspective
Space Science Reviews, 2016Co-Authors: Michael V. Kurgansky, Ralph D. Lorenz, T. Takemi, Nilton O. Renno, Wei WeiAbstract:Simple analytical models for the flow structure of Dust Devils in steady state, and a “thermophysical” scaling theory that explains how these flow structures are maintained are reviewed. Then, results from high-resolution numerical simulations are used to provide insights into the structure of Dust-Devil-like vortices and study the impact of surface roughness on them. The article concludes with an overview of the influence of lofted Dust on the flow structure of Dust Devils and a discussion of open questions.
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heuristic estimation of Dust Devil vortex parameters and trajectories from single station meteorological observations application to insight at mars
Icarus, 2016Co-Authors: Ralph D. LorenzAbstract:Abstract A physically-realistic migrating vortex model is developed and applied to generate pressure and wind speed and direction histories for Dust Devil passage. The asymmetric character of wind histories is noted, and we examine how these combined data constrain the solution space of Dust Devil parameters (migration velocity, diameter and intensity), ambient wind, and miss distance. These histories are compared with a new terrestrial field dataset of high-time resolution pressure and wind measurements of over twenty Dust Devil encounters in New Mexico. This new dataset is made available electronically and it is found that model fits can be typically achieved with simultaneous root-mean-square errors of ∼0.05 hPa (∼5–10% of the peak pressure signature), ∼20°of wind azimuth, and ∼2 m/s windspeed. The fits are not unique, however, and some heuristic aspects of resolving the intrinsic degeneracies of the problem and nonideal features of real encounters are discussed. The application of this approach to the InSight lander is noted, offering the possibility of defining the context for any possible detections of electromagnetic and seismic signatures of Dust Devils on Mars.
William M. Farrell - One of the best experts on this subject based on the ideXlab platform.
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the martian Dust Devil electron avalanche laboratory measurements of the e field fortifying effects of Dust electron absorption
Icarus, 2017Co-Authors: William M. Farrell, J L Mclain, M R Collier, John W KellerAbstract:Abstract Analogous to terrestrial Dust Devils, charged Dust in Mars Dust Devils should become vertically stratified in the convective features, creating large scale E-fields. This E-field in a Martian-like atmosphere has been shown to stimulate the development of a Townsend discharge (electron avalanche) that acts to dissipate charge in regions where charge build-up occurs. While the stratification of the charged Dust is a source of the electrical energy, the uncharged particulates in the Dust population may absorb a portion of these avalanching electrons, thereby inhibiting dissipation and leading to the development of anomalously large E-field values. We performed a laboratory study that does indeed show the presence of enhanced E-field strengths between an anode and cathode when Dust-absorbing filaments (acting as particulates) are placed in the avalanching electron flow. Further, the E-field threshold condition to create an impulsive spark discharge increases to larger values as more filaments are placed between the anode and cathode. We conclude that the spatially separated charged Dust creates the charge centers and E-fields in a Dust Devil, but the under-charged portion of the population acts to reduce Townsend electron dissipation currents, further fortifying the development of larger-than-expected E-fields.
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Martian Dust Devil electron avalanche process and associated electrochemistry
Journal of Geophysical Research, 2010Co-Authors: T. L. Jackson, William M. Farrell, Gregory T. Delory, Jeyasingh NithianandamAbstract:[1] Mars' dynamic atmosphere displays localized Dust Devils and larger, global Dust storms. Based on terrestrial analog studies, electrostatic modeling, and laboratory work, these features will contain large electrostatic fields formed via triboelectric processes. In the low-pressure Martian atmosphere, these fields may create an electron avalanche and collisional plasma due to an increase in electron density driven by the internal electrical forces. To test the hypothesis that an electron avalanche is sustained under these conditions, a self-consistent atmospheric process model is created including electron impact ionization sources and electron losses via Dust absorption, electron dissociation attachment, and electron/ion recombination. This new model is called the Dust Devil Electron Avalanche Model (DDEAM). This model solves simultaneously nine continuity equations describing the evolution of the primary gaseous chemical species involved in the electrochemistry. DDEAM monitors the evolution of the electrons and primary gas constituents, including electron/water interactions. We especially focus on electron dynamics and follow the electrons as they evolve in the E field driven collisional gas. When sources and losses are self-consistently included in the electron continuity equation, the electron density grows exponentially with increasing electric field, reaching an equilibrium that forms a sustained time-stable collisional plasma. However, the character of this plasma differs depending upon the assumed growth rate saturation process (chemical saturation versus space charge). DDEAM also shows the possibility of the loss of atmospheric methane as a function of electric field due to electron dissociative attachment of the hydrocarbon. The methane destruction rates are presented and can be included in other larger atmospheric models.
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A model of the ULF magnetic and electric field generated from a Dust Devil
Journal of Geophysical Research, 2006Co-Authors: William M. Farrell, G. T. Delory, Steven A. Cummer, John Marshall, M. D. DeschAbstract:[1] It has been demonstrated that terrestrial Dust Devils emit ULF magnetic radiation. On Mars, Dust Devils may also generate such magnetic emissions, which might be used as a hazard alert for manned missions. Specifically, grains in Dust Devils become charged via contact electrification, and it has been proposed that the cyclonic motion of these charged grains in the vortex wind fields accounts for the magnetic emission. To test this hypothesis in general and the possible Mars application, a computer simulation of the contact electrification/wind blowing phenomena was created, with the charge distribution and resulting magnetic fields monitored as a function of time. The results indicate that indeed a fluctuating charge distribution in a vortex wind can account for the ULF magnetic fields measured from a Dust Devil. The contact electrification process is a function of composition, and we demonstrate that the various compositions will give rise to different magnetic field responses from the Dust Devil. We also demonstrate that this system of swirling charged grains develops vertical currents and associated electric fields, as suggested in preceding works.
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A simple electrodynamic model of a Dust Devil
Geophysical Research Letters, 2003Co-Authors: William M. Farrell, G. T. Delory, Steven A. Cummer, John MarshallAbstract:[1] We present an electrodynamic model of a Dust Devil applying a similar methodology as performed previously for charging in terrestrial thunderstorms. While thunderstorm processes focus on inductive charging between large graupel and smaller ice and water droplets, we tailor the model to focus on the electric charge transfer between Dust grains of different sizes and compositions. We specifically compare and contrast the triboelectric Dust charging processes presented previously in Melnik and Parrot [1998] and Desch and Cuzzi [2000] in the development of macroscopic Dust Devil electric fields. We find that large vertical E-fields (∼20 kV/m) can develop in the Devil.
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ULF and ELF magnetic activity from a terrestrial Dust Devil
Geophysical Research Letters, 2003Co-Authors: Jeffrey G. Houser, William M. Farrell, S M MetzgerAbstract:[1] Terrestrial Dust Devils are known to be triboelectric generators: electric charge is generated and exchanged via the mixing and colliding of moving grains. Static electric fields from the structures have been previously reported, this in excess of 1/2 kV/m at a couple hundred meters from the Devil. In this work, we report on AC magnetic measurements made during the passage of an intense similar to10-m wide, couple hundred-meter tall Dust Devil in the Nevada desert. The Devil-related magnetic activity appears in two forms: Impulsive extremely-low-frequency (ELF: 30-300 Hz) static discharges to the instrument as the sensor became immersed directly into the Devil's electrified Dust and ultra-low-frequency (ULF: 3-30 Hz), continuous emissions that were sensed remotely as the storm approached and receded from the mobile station. The latter is a new finding not previously reported. Such measurements not only prove that individual Dust grains within the Devil are charged, but that the grains are transported in bulk to form an extended, coherent radiation source.
Patrick L. Whelley - One of the best experts on this subject based on the ideXlab platform.
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gusev crater mars observations of three Dust Devil seasons
Journal of Geophysical Research, 2010Co-Authors: R Greeley, Lynn D V Neakrase, M T Lemmon, D Waller, Nathalie A Cabrol, Geoffrey A Landis, Mary Pendleton Hoffer, S D Thompson, Patrick L. WhelleyAbstract:[1] Spirit began operations in Gusev Crater in January 2004 and has returned data on three seasons of Dust Devil (DD) activity. Total DDs observed were 533 in season one, 101 in season two, and 127 in season three. Their general characteristics are the same within factors of 2 among the seasons, with median diameters of 19 m in season one, 24 m in season two, and 39 m in season three, and Dust flux values for individual vortices ranging from 4.0 × 10−9 to 4.6 × 10−4 kg m−2 s−1 in season one, 5.2 × 10−7 to 6.2 × 10−5 kg m−2 s−1 in season two, and 1.5 × 10−7 to 1.6 × 10−4 kg m−2 s−1 in season three. All three seasons were initiated with the onset of southern Martian spring within 14 sols of the same Ls (181°) and their frequency increased to the period corresponding to late southern spring. The occurrences decreased monotonically in seasons one and three but apparently ended abruptly in season two when a large Dust storm occurred; although the Dusty atmosphere might have precluded the detection of active DDs, the abrupt cessation could result from conditions such as thermal stability of the atmosphere due to the presence of Dust which could halt DD formation. Dust Devils can contribute significant quantities of Dust to the atmosphere, although it is unclear as to whether this Dust stays locally or is injected into higher-altitude winds and is distributed elsewhere. In the three DD seasons observed through Spirit, DDs in Gusev Crater injected a minimum average of ∼18 × 106 kg of material into the atmosphere each season.
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Dust Devil speeds directions of motion and general characteristics observed by the mars express high resolution stereo camera
Icarus, 2008Co-Authors: Christina Stanzel, Patrick L. Whelley, M Patzold, D A Williams, R Greeley, Gerhard NeukumAbstract:Abstract A total of 205 Dust Devils were detected in 23 High Resolution Stereo Camera (HRSC) images taken between January 2004 and July 2006 with the ESA Mars Express orbiter, in which average Dust Devil heights were ∼660 m and average diameters were ∼230 m. For the first time, Dust Devil velocities were directly measured from orbit, and range from 1 to 59 m/s. The observed Dust Devil directions of motion are consistent with data derived from a General Circulation Model (GCM). In some respects HRSC Dust Devil properties agree favorably with data from the NASA Mars Exploration Rover Spirit Dust Devil analyses. The spatial distribution of the active Dust Devils detected by HRSC supports the conjecture that the ascending branch of the Hadley circulation is responsible for the increase in Dust Devil activity, especially observed during southern summer between 50° and 60° S latitude. Combining the Dust-lifting rate of 19 kg/km2/sol derived from the Spirit observations with the fewer in number but larger in size Dust Devils from various other locations observed by HRSC, we suggest that Dust Devils make a significant contribution to the Dust entrainment into the atmosphere and to the martian Dust cycle.
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The distribution of Dust Devil activity on Mars
Journal of Geophysical Research, 2008Co-Authors: Patrick L. Whelley, Ronald GreeleyAbstract:[1] Martian Dust Devil activity, inferred from their tracks, is mapped globally and compared to surface and atmospheric properties. Dust Devils are estimated to lift 2.3 ± 1 × 1011 kg of Dust each year, mostly from two narrow bands near 60°N and 60°S, during their respective spring and summer. Approximately 55% of the Dust lifted by Dust Devils in the northern hemisphere is removed from within 45 and 75°N, while 65% of that lifted in the south is from within 45 and 75°S. The southern band is an order of magnitude more populated with tracks than in the north, likely a result of Mars' orbital eccentricity. The equator is the location of a lesser peak, while few Dust Devil tracks are found at the poles and middle latitudes. During the fall and winter in both hemispheres, few tracks are observed. Dust Devil and track formation does not appear to be controlled significantly by elevation, topographic slope, Dust cover, or surface physical properties. Dust Devils annually lift approximately half as much material as local and regional Dust storms and are therefore significant contributors of Dust into the Martian atmosphere.
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results from automated cloud and Dust Devil detection onboard the mer
2008Co-Authors: Steve Chien, Patrick L. Whelley, R Greeley, Rebecca Castano, Benjamin Bornstein, Alex Fukunaga, Andres Castano, Jeffrey Biesiadecki, M T LemmonAbstract:We describe a new capability to automatically detect Dust Devils and clouds in imagery onboard rovers, enabling downlink of just the images with the targets or only portions of the images containing the targets. Previously, the MER rovers conducted campaigns to image Dust Devils and clouds by commanding a set of images be collected at fixed times and downloading the entire image set. By increasing the efficiency of the campaigns, more campaigns can be executed. Software for these new capabilities was developed, tested, integrated, uploaded, and operationally checked out on both rovers as part of the R9.2 software upgrade. In April 2007 on Sol 1147 a Dust Devil was automatically detected onboard the Spirit rover for the first time. We discuss the operational usage of the capability and present initial Dust Devil results showing how this preliminary application has demonstrated the feasibility and potential benefits of the approach.
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latitudinal dependency in Dust Devil activity on mars
Journal of Geophysical Research, 2006Co-Authors: Patrick L. Whelley, R GreeleyAbstract:[1] There are more Dust Devils (dd; inferred from Dust Devil tracks, or ddt) in the southern hemisphere than in the north. Ddt suggest that the dd season starts in late spring (Ls = 60° and 240°, northern and southern hemispheres, respectively) and continues through the summer into mid fall (Ls = 210° and 30°, northern and southern hemispheres, respectively). However, the ddt density in the southern hemisphere averages ∼0.6 ddt/km2, while the northern hemisphere averages ∼0.06 ddt/km2, or an order of magnitude less. This is attributed to the observation that in southern summer the surface receives 40% more solar energy for atmospheric motion and dd formation than the surface in the northern summer, due to the eccentricity of Mars' orbit.
S M Metzger - One of the best experts on this subject based on the ideXlab platform.
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Field measurements of horizontal forward motion velocities of terrestrial Dust Devils: Towards a proxy for ambient winds on Mars and Earth
Icarus, 2012Co-Authors: M. R. Balme, S M Metzger, Aymeric Spiga, L K Fenton, A. Pathare, M. C. Towner, S. R. Lewis, N. O. Renno, H. M. Elliott, F. A. SacaAbstract: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. (C) 2012 Elsevier Inc. All rights reserved.
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evidence of Dust Devil scour at the mer spirit gusev site
36th Annual Lunar and Planetary Science Conference, 2005Co-Authors: S M MetzgerAbstract:Introduction: Using MOC orbital images and several image sets from MER Spirit (Pancam, Navcam and MI), it has now become possible to study at substantially different scales the effects of Dust Devil vortices as they pass over the surface of the planet Mars. Prior to the January 2004, landing of the Mars Exploration Rover Spirit in Gusev crater, MOC images indicated a number of Dust Devil tracks in the immediate area. This report will make the case for (1) a limited number of days when vortex formation could proceed, (2) Dust Devil scour evidence on a rock examined by the Microscopic Imager (MI), and (3) calculate Dust removal rates during one season in Gusev. Gusev Dust Devil Tracks: MOC image R0701606-04 covers 2.95 x 12.06 km at 1.44 m/pxl and includes the Spirit landing site atop numerous Dust Devil tracks. The central track cluster has too many overlapping trails to count. Along the cluster perimeter and North of Spirit’s landing site are at least two distinct families of track orientations (NW >> SE, and W >> E). There are two prominent size clusters (many small/medium, and a few huge [=250m max.]). Thus, this portion of the Gusev Dust Devil track field may represent a mere two days of activity. If so, one of those days spawned a few big vortices among the common mid-sized batch. The other day spawned more numerous but more restrained diameter vortices, apparently immediately following eachother off the trigger points (as offset parallel tracks, similar to foreset bedding where bounding conditions remain stable while an intermediate condition, in this case wind, gently & progressively shifts). Windward crater rims clearly provide trigger points, producing track swarms in their lee. Figure 1:
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A close encounter with a terrestrial Dust Devil
2004Co-Authors: Martin C. Towner, S M Metzger, Matthew Balme, Ronald Greeley, Manish R. Patel, T. J. Ringrose, John C. ZarneckiAbstract:We report on an extremely well characterised encounter with a terrestrial Dust Devil, and its comparison with martian Dust Devils.
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ULF and ELF magnetic activity from a terrestrial Dust Devil
Geophysical Research Letters, 2003Co-Authors: Jeffrey G. Houser, William M. Farrell, S M MetzgerAbstract:[1] Terrestrial Dust Devils are known to be triboelectric generators: electric charge is generated and exchanged via the mixing and colliding of moving grains. Static electric fields from the structures have been previously reported, this in excess of 1/2 kV/m at a couple hundred meters from the Devil. In this work, we report on AC magnetic measurements made during the passage of an intense similar to10-m wide, couple hundred-meter tall Dust Devil in the Nevada desert. The Devil-related magnetic activity appears in two forms: Impulsive extremely-low-frequency (ELF: 30-300 Hz) static discharges to the instrument as the sensor became immersed directly into the Devil's electrified Dust and ultra-low-frequency (ULF: 3-30 Hz), continuous emissions that were sensed remotely as the storm approached and receded from the mobile station. The latter is a new finding not previously reported. Such measurements not only prove that individual Dust grains within the Devil are charged, but that the grains are transported in bulk to form an extended, coherent radiation source.
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Dust Devil vortices seen by the mars pathfinder camera
Geophysical Research Letters, 1999Co-Authors: S M Metzger, James R. Carr, T.j. Parker, J.r. Johnson, Mark T. LemmonAbstract:Discovery of Dust Devil vortices in Mars Pathfinder (MPF) images reveals a Dust entrainment mechanism at work on Mars. Scattering of visible light by Dust in the Martian atmosphere creates a pronounced haze, preventing conventional image processing from displaying Dust plumes. Spectral differencing techniques have enhanced five localized Dust plumes from the general haze in images acquired near midday, which we determine to be Dust Devils. Processing of 440 nm images highlights Dust Devils as distinct occultation features against the horizon. The Dust Devils are interpreted to be 14–79 m wide, 46–350 m tall, travel at 0.5–4.6 m/s, with Dust loading of 7E-5 kg m-3, relative to the general haze of 9E-8 kg m-3, and total particulate transport of 2.2–700 kg. The vortices match predictions from terrestrial analog studies.
Michael V. Kurgansky - One of the best experts on this subject based on the ideXlab platform.
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Dust Devil Steady-State Structure from a Fluid Dynamics Perspective
Space Science Reviews, 2016Co-Authors: Michael V. Kurgansky, Ralph D. Lorenz, T. Takemi, Nilton O. Renno, Wei WeiAbstract:Simple analytical models for the flow structure of Dust Devils in steady state, and a “thermophysical” scaling theory that explains how these flow structures are maintained are reviewed. Then, results from high-resolution numerical simulations are used to provide insights into the structure of Dust-Devil-like vortices and study the impact of surface roughness on them. The article concludes with an overview of the influence of lofted Dust on the flow structure of Dust Devils and a discussion of open questions.
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History and Applications of Dust Devil Studies
Space Science Reviews, 2016Co-Authors: Ralph D. Lorenz, Dennis Reiss, Matthew R. Balme, Angelo Pio Rossi, Manish R. Patel, Michael V. Kurgansky, Martina Klose, Henrik Kahanpää, Aymeric SpigaAbstract:Studies of Dust Devils, and their impact on society, are reviewed. Dust Devils have been noted since antiquity, and have been documented in many countries, as well as on the planet Mars. As time-variable vortex entities, they have become a cultural motif. Three major stimuli of Dust Devil research are identified, nuclear testing, terrestrial climate studies, and perhaps most significantly, Mars research. Dust Devils present an occasional safety hazard to light structures and have caused several deaths.
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Micrometeorological Conditions for Dust-Devil Occurrence in the Atacama Desert
Boundary-Layer Meteorology, 2010Co-Authors: Michael V. Kurgansky, Aldo Montecinos, Victor Villagran, Stephen M. MetzgerAbstract:We report on field observations in January 2009 (austral summer) of atmospheric Dust Devils in the northern part of the Atacama Desert in South America (≈20◦S). An extremely high level of Dust-Devil activity over the study site has been observed, dependent on local meteorological conditions. We found a high correlation between the Dust-Devil frequency of occurrence and the Obukhov length scale, L, calculated from meteorological gradient measurements, with a clear tendency for this frequency to increase with decreasing −L. The upper threshold values of −L ≈ 20–30 m, and the 2-m mean wind speed, V 2 ≈ 8m s−1, for Dust-Devil occurrence have been found, but the minimal V 2 threshold was not observed. Parallel routine meteorological measurements enabled us to calculate the main constituents of the surface energy balance, to obtain direct estimates of the surface albedo (α ≈ 0.21 at the solar noon) and to summarize the local conditions.
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A simple model of the magnetic emission from a Dust Devil
Journal of Geophysical Research, 2007Co-Authors: Michael V. Kurgansky, Leonardo Baez, E.m. OvalleAbstract:[1] A simple Rankine-like vortex model of the Dust Devil behaving as a magnetic solenoid has been constructed. It is augmented with a one-dimensional model describing steady vertical distribution of the electric charge in the Dust Devil. For terrestrial Dust Devils, the model permits uniform vertical distribution of the negatively charged Dust within the main vortex flow. For higher electric conductivity of air on Mars, the model hints on a rapid decay with altitude of the Dust electrification, with e-folding height order of several tens of meters, which is much less than the total Dust column height. It is shown that some characteristic features of recently discovered ULF magnetic emission from the terrestrial Dust Devil can be interpreted in terms of interaction between negatively charged smaller-scale vortex filaments inside the main vortex. It is conjectured that such ULF magnetic emission should be accompanied by the emission of sound waves of approximately doubled frequency.
