共查询到20条相似文献，搜索用时 31 毫秒
1.
An integrated laser anemometer and dust accumulator for studying wind-induced dust transport on Mars
J.P. Merrison H.P. Gunnlaugsson K. Kinch T.L. Jacobsen A.E. Jensen P. Nørnberg H. Wahlgreen 《Planetary and Space Science》2006,54(11):1065-1072
Windborne dust is one of the most important and dynamic factors affecting the Martian surface and its atmosphere, yet there lacks a detailed physical understanding how it is transported. We present a miniature laser-based optoelectronic instrument for use on a Mars lander. It integrates sensors capable of quantifying important parameters needed for the understanding and modeling of dust transport on Mars, these include wind speed, wind direction, suspended dust concentration, dust deposition and removal rates as well as the electrification of the Martian dust. Dust electrification has been seen from experimental simulations to be of considerable importance to the processes of adhesion and cohesion, specifically prompting the formation of low mass density dust aggregates. Testing of this prototype instrument has been performed under simulated Martian conditions in a wind tunnel facility. The results and analysis of its functionality will be presented. 相似文献
2.
P. Nørnberg H.P. Gunnlaugsson J.P. Merrison A.L. Vendelboe 《Planetary and Space Science》2009,57(5-6):628-631
A fine grained magnetic iron oxide precipitate found in Denmark has been studied with regard to grain size, magnetic properties, aerosol transport, grain electrification, aggregation and optical reflectance. It has shown itself to be a good Martian dust analogue. The fraction of the Salten Skov I soil sample <63 μm was separated from the natural sample by dry sieving. This fraction could be dispersed by ultrasonic treatment into grains of diameter ～1 μm, in reasonable agreement with suspended dust grains in the Martian atmosphere estimated from the Viking, Pathfinder and Mars Exploration Rover missions. Though mineralogical and chemical differences exist between this analogue and Martian dust material, in wind tunnel experiments many of the physical properties of the atmospheric dust aerosol are reproduced. 相似文献
3.
Dust is a major environmental factor on the surface and in the atmosphere of Mars. Knowing the electrical charge state of this dust would be of both scientific interest and important for the safety of instruments on the Martian surface. In this study the first measurements have been performed of dust electrification using suspended Mars analogue material. This has been achieved by attracting suspended dust onto electrodes placed inside a Mars simulation wind tunnel. The Mars analogue used was from Salten Skov in Denmark, this contained a high concentration of ferric oxide precipitate. Once suspended, this dust was found to consist of almost equal quantities of negatively (46±6%) and positively (44±15%) charged grains.These grains were estimated to typically carry a net charge of around 105e, this is sufficient to dominate the processes of adhesion and cohesion of this suspended dust. Evidence is presented for electrostatic aggregation of the dust while in suspension. Development of a simple instrument for measuring electrical charging of the suspended dust on Mars will be discussed. 相似文献
4.
J.P. Merrison H.P. Gunnlaugsson M.R. Hogg M. Jensen J.M. Lykke M.Bo Madsen M.B. Nielsen P. Nørnberg T.A. Ottosen R.T. Pedersen S. Pedersen A.V. Sørensen 《Planetary and Space Science》2012,60(1):328-335
The electrification of wind-blown dust grains was studied in a series of laboratory experiments to examine how grain electrification depends on grain size, grain mineralogy, atmospheric composition, atmospheric pressure, and the method of dust dispersal. This work is intended to contribute to a deeper physical understanding of particle electrification on both Mars and Earth. Findings indicate that the amount of electrification per suspended particle generally is independent of dust entrainment process and atmospheric composition. As expected, the electrification process is grain size-dependent, with smaller grains predominantly electrifying negatively. Although there appears to be a weak dependence upon dust mineralogy, this work supports the expectation that dust suspended in the Martian atmosphere will be significantly electrified. 相似文献
5.
Physical characteristics of naturally formed convective vortices in the Phoenix Mars lander environment have been investigated on a relatively hot summer Martian arctic day. For this, the NCAR LES has been adapted and developed to conduct three micro-scale simulations of the Martian Convective Boundary Layer (CBL), in situations with and without geostrophic wind, and atmospheric radiative flux divergence. Time series analysis of the vortices’ properties is discussed. The study confirms the decrease of vortex populations in windy conditions and also illustrates that intense but small vortices are expected to be observed in higher geostrophic wind situations. This may lead to more dust migration rather than dust devil formation on windy days. The background (geostrophic) wind causes the vortices to become less cyclostrophically balanced. 相似文献
6.
H.P. Gunnlaugsson K.M. Kinch J.P. Merrison H. Wahlgreen 《Planetary and Space Science》2004,52(8):693-698
A new optical instrument has been developed to precisely measure the local accumulation of dust particles on a surface. This device can be used in combination with applied magnetic or electric fields in order to investigate physical properties of the dust and its interactions with the surface. In this prototype instrument, permanent magnets were used to capture suspended magnetic dust in a Mars simulation wind tunnel. The scientific objectives that may be addressed with such a device are discussed. 相似文献
7.
8.
Ronald Greeley 《Planetary and Space Science》2002,50(2):151-155
Experiments were conducted under atmospheric pressures appropriate for Earth and Mars to determine the efficiency of sand in saltation as a means for raising dust into the atmosphere under wind speeds which would otherwise be too low for dust entrainment. Experiments involving intimate mixtures of sand and dust (1:1 ratio by mass) showed that after an initial flurry of activity of a few seconds duration, the bed stabilized with little movement of either sand or dust. In contrast, sands set into saltation upwind from dust beds were efficient in injecting the dust into suspension, with low-pressure Martian conditions being some five times more efficient than terrestrial conditions. This result is attributed to the higher kinetic energies of the saltating grains on Mars, which is a consequence of the higher velocities of the grains. These results suggest that sands saltating across dust beds on Mars are an effective means for setting dust into suspension. 相似文献
9.
This work is devoted to the analysis of the variation of albedo measured by orbiting instruments with atmospheric opacity on Mars. The study has been conduced by analysing Mars Global Surveyor Thermal Emission Spectrometer (MGS-TES) data from martian regions with different surface albedo.In support of these data, synthetic spectra with different surface albedo and atmospheric opacities have been computed, so that a comparison has been performed. The synthetic spectra have been retrieved by using two different grain sizes for suspended dust (0.5 and 1.2 μm), allowing a comparison between the two models and the observations.Using the DCI, a parameter describing the quantity of dust deposited on the surface, the effectiveness of the single scattering approximation has been tested for low atmospheric opacity by analysing the quality of the linear fit up to different atmospheric opacity.For more opaque conditions two kinds of fits have been applied to the data, linear and second-order degree polynomial. In this case, we found that the polynomial fit better describes the observations.The analysis of these data made it possible to notice a peculiar trend, already reported by Christensen (1988), of the albedo over Syrtis Major after the occurrence of dust storms, but, differently from that work, now the study of DCI together with atmospheric opacity and albedo allowed us to robustly confirm the hypothesis made by Christensen.Finally, the comparison between observations and synthetic spectra computed with models with different particles grain sizes indicates that dust particles of 0.5 μm diameter are the most effective to change the aerosol atmospheric opacity on Mars. 相似文献
10.
A method for separating the spectral signatures of the Martian surface and atmosphere was developed and is applied to multiple emission angle data returned from the MGS TES instrument. This method includes correlated-k and index gas removal algorithms that may be applied to all nadir-pointing TES data. Initial results have provided new and refined measurements of the spectral shapes of atmospheric dust and the Martian surface. Surface temperatures and atmospheric dust opacities are also retrieved with improved accuracy over single observation temperature and opacity retrievals. Low-albedo surfaces display absorptions consistent in both shape and depth with previous studies. These surfaces may be closely modeled using a combination of previously derived basalt, andesitic, and high-albedo surface spectral shapes. Short wavelengths display no significant absorptions, indicating both the coarse particulate nature of the surface and the lack of significant amounts of carbonate. Moderate- and high-albedo surfaces have spectral shapes distinctive of fine particulate silicate materials. No single material can match the entire high-albedo surface spectrum, though there are clear indications of a material that closely matches intermediate to calcic plagioclase and an emission peak at ∼1620 cm−1 due to bound water. The lack of residual restrahlen silicate absorptions indicates that minerals such as olivine or pyroxene are not present in high-albedo surfaces at significant (but unknown) abundances. High-albedo surface results presented here are in agreement with and complementary to shorter wavelength observations. The Martian dust is composed of both primary and secondary minerals. Either chemical weathering has not completely altered its source material or the soil is a mixture of altered and unaltered sources. Further laboratory studies are needed to better establish detection limits and behavior of mineral mixtures of fine particulates in the thermal infrared portion of the spectrum. 相似文献
11.
Experimental results are presented of wind induced grain detachment under Mars simulation conditions. A simple force balance equation is applied to quantify the wind shear stress required for removal of glass spheres from a sand bed. The transport of fine grained martian dust is simulated by the detachment of hollow glass spheres which resemble low mass density dust aggregates observed to form during simulations when using Mars analogue material. The results agree well with observations of dust removal and wind speed measurements made by the NASA Viking landers at the martian surface. This work supports the suggestion that dust aggregate fragmentation allows wind induced dust entrainment at substantially lower wind shear than that of solid sand grains and has direct application to the study of global dust transport and martian climatology. 相似文献
12.
Recent probes of the planet Venus reveal a probable surface temperature exceeding 700K and a pressure exceeding 100 atm. A very dusty lower atmosphere may exist which is composed of micron-sized particles kept airborne by mild turbulence and a gentle circulation of deep adiabatic currents. A study of surface conditions responsible for generation and persistence of surface dust clouds is of fundamental importance in the radiative and dynamic properties of the atmosphere. Also spurious radar echoes may be caused by suspended particulate matter, thus explaining the high relief reported by radar altimeters.Equations describing transportation and deposition of dust and sand have been solved for the surface conditions of Venus. It is concluded that the minimum wind velocity for initiating grain movement is about one order of magnitude smaller than on Earth. In addition, this minimum wind velocity occurs for smaller particles on Venus than on Earth. Once the particles are raised, they can be maintained aloft for longer periods of time and over a larger size range on Venus.Surface structures such as ripples evolved from aeolian deposition are likely to be of smaller vertical dimensions but larger horizontally when compared with equivalent structures on Earth. 相似文献
13.
Leonard J. Martin 《Icarus》1984,57(3):317-321
This note is an attempt to resolve some misconceptions regarding the historical record of the Martian atmospheric phenomena referred to as “dust storms,” but often called yellow storms, yellow clouds, planetwide dust storms, global dust storms, great dust storms, etc. The known frequency of planet-encircling storms will be specifically addressed. Better knowledge of the sizes, frequencies, and locations of Martian dust storms is needed for atmospheric modeling and for future mission planning. 相似文献
14.
L. Colangeli J.J. Lopez-Moreno P. Nørnberg V. Della Corte F. Esposito E. Mazzotta Epifani J. Merrison C. Molfese P. Palumbo J.F. Rodriguez-Gomez A. Rotundi G. Visconti J.C. Zarnecki 《Planetary and Space Science》2009,57(8-9):1043-1049
Dust and water vapour are fundamental components of the Martian atmosphere. In view of tracing the past environmental conditions on Mars, that possibly favoured the appearing of life forms, it is important to study the present climate and its evolution. Here dust and water vapour have (and have had) strong influence. Of major scientific interest is the quantity and physical, chemical and electrical properties of dust and the abundance of water vapour dispersed in the atmosphere and their exchange with the surface. Moreover, in view of the exploration of the planet with automated systems and in the future by manned missions, it is of primary importance to analyse the hazards linked to these environmental factors. The Martian Environmental Dust Systematic Analyser (MEDUSA) experiment, included in the scientific payload of the ESA ExoMars mission, accommodates a complement of sensors, based on optical detection and cumulative mass deposition, that aims to study dust and water vapour in the lower Martian atmosphere. The goals are to study, for the first time, in-situ and quantitatively, physical properties of the airborne dust, including the cumulative dust mass flux, the dust deposition rate, the physical and electrification properties, the size distribution of sampled particles and the atmospheric water vapour abundance versus time. 相似文献
15.
Experimental data on cohesion-free particle transport in fluid beds are applied, via a universal scaling relation, to atmospheric transport of fine grains on Mars. It may be that cohesion due to impact vitrification, vacuum sintering, and adsorbed thin films of water are absent on Mars—in which case the curve of threshold velocity versus grain size may show no turnup to small particle size, and one micron diameter grains may be injected directly by saltation into the Martian atmosphere more readily than 100 micron diameter grains. Curves for threshold and terminal velocities are presented for the full range of Martian pressures and temperatures. Suspension of fine grains is significantly easier at low temperatures and high pressures; late afternoon brightenings of many areas of Mars, and the generation of dust storms in such deep basins as Hellas, may be due to this effect. 相似文献
16.
Walter Fernández 《Earth, Moon, and Planets》1995,70(1-3):183-191
The surface temperature of the Martian polar caps is about 148 K (frost point temperature of CO2 at a surface pressure of about 6 hPa), with the “desert” (frost-free) areas adjacent to the polar caps having much greater surface temperatures. The existence of this steep meridional gradient of temperature between the polar caps and the adjacent “desert” areas may produce in the atmosphere a baroclinic instability which generates an atmospheric circulation system similar in some aspects to the terrestrial sea breeze. We have called this circulation system the Martian polar cap breeze. In this paper, the phenomenology of the Martian polar cap breeze is developed on the basis of the indirect observational evidence. Along with friction and the Coriolis force, other factors influence the polar cap breeze: the prevailing wind, topography, irregularity of the polar cap-edge, and stability of the atmosphere. These factors are studied in a qualitative form, as well as the seasonal variations. In addition, the large-scale polar cap wind is presented as a different Martian atmospheric circulation system. 相似文献
17.
An experimental study was undertaken to determine how the spectral and photometric properties of representative Martian areas are affected by fallout of atmospheric dust suspended during dust forms. A laboratory apparatus was used to simulate the uniform fallout and deposition of particles 1 to 5 μm in diameter. Spectral measurements from 0.4- to 1.2-μm wavelengths and photometric measurements at several wavelengths were made for a number of Mars-analog materials before and after deposition of 6 × 10?5 to 1.5 × 10?3 g/cm2 of simulated fallout. These results indicate that the spectral and photometric properties of Martian regions can be affected significantly even by minute amounts of fallout. For instance, the reflectance at 0.56 μm of an average dark area will increase by 35% after deposition of only 9 × 10?5 g/cm2, and by 70% after deposition of 1.5 × 10?4 g/cm2. Thus the fallout from even one dust storm season (～2 × 10?3 g/cm2) is sufficient to change significantly the spectral and photometric characteristics of the substrate material, if the fallout were ubiquitous over the surface and if no competing processes of dust removal from surface grains occured. 相似文献
18.
The results are presented of a preliminary study that aims to validate the hypothesis about the possibility of the formation of a giant dust devil resulting from the interaction of the wind with the dust clouds initiated by the impacts of meter meteoroids on the Martian surface. The laboratory experiment allowed us to examine the dynamics in the wind field of the dust ejection, whose characteristics corresponded qualitatively to the features of a dust ejection induced by the meteoroid impact. It follows from numerical computations, which are validated to some extent by comparison with the results of laboratory simulation, that the wind flowing around a dust column results in a generation of vertical eddy structures. The interaction of these structures with a convective flow, which is formed, for example, as a result of the solar heating of dusty regions, can cause the development of a dust devil. 相似文献
19.
Emilie Gardin Pascal Allemand Cathy Quantin Simone Silvestro Christophe Delacourt 《Planetary and Space Science》2012,60(1):314-321
Dunes have similar morphologies on the Earth and Mars. The main differences between Martian and terrestrial dunes are their size, which is larger on Mars, and their duration of formation, which is longer on Mars. As the characteristic time of Martian dunes is in the same order as that of the Martian climatic oscillations, Martian dunes could be recorders of past winds regimes and past climates. In order to test this hypothesis, we performed a morphological study of 550 dune fields with high resolution images and we inferred the directions of the dune formative winds from the orientation of the dune slip faces. Our study shows that 310 dune fields record one to four distinct wind directions with some geometric patterns that do not exist on the Earth such as barchans built by opposite wind directions coexisting in the same dune field. Our study demonstrates that the inferred formative wind directions are only partially in agreement with the current wind-patterns predicted by General Circulation Models (GCM). Several possible causes for the misalignment between dunes and GCM outputs are discussed: these include the local variation of the global circulation due to local topographic effects or the possibility that these dunes could be in a transient geometry or fossil. Such bedforms are considered indeed to be not in equilibrium with the present-day atmospheric conditions. This latter hypothesis is supported by the presence, in some ergs, of closely spaced dunes showing nearly opposite slip face orientations. Therefore, we propose that Martian dune fields are constituted, in some cases, by active and fossil dunes and therefore have the potential to preserve information on paleoclimates over extensive periods. 相似文献