scholarly journals Configuration of the Martian dust rings: shapes, densities, and size distributions from direct integrations of particle trajectories

2020 ◽  
Vol 500 (3) ◽  
pp. 2979-2985
Author(s):  
Xiaodong Liu ◽  
Jürgen Schmidt
Keyword(s):  
Size Range ◽  
Solar Radiation Pressure ◽  
Dust Particles ◽  
Size Distributions ◽  
Grain Sizes ◽  
Gravitational Perturbations ◽  
Ring Configuration ◽  
Upper Limits ◽  
Configuration Simulation ◽  
Fifth Order

ABSTRACT It is expected since the early 1970s that tenuous dust rings are formed by grains ejected from the Martian moons Phobos and Deimos by impacts of hypervelocity interplanetary projectiles. In this paper, we perform direct numerical integrations of a large number of dust particles originating from Phobos and Deimos. In the numerical simulations, the most relevant forces acting on the dust are included: Martian gravity with spherical harmonics up to fifth degree and fifth order, gravitational perturbations from the Sun, Phobos, and Deimos, solar radiation pressure, as well as the Poynting–Robertson drag. In order to obtain the ring configuration, simulation results of various grain sizes ranging from submicrometres to 100 μm are averaged over a specified initial mass distribution of ejecta. We find that for the Phobos ring grains smaller than about 2 μm are dominant; while the Deimos ring is dominated by dust in the size range of about 5–20 μm. The asymmetries, number densities, and geometric optical depths of the rings are quantified from simulations. The results are compared with the upper limits of the optical depth inferred from Hubble observations. We compare to previous work and discuss the uncertainties of the models.

scholarly journals Subglacial comminution in till — evidence from microfabric studies and grain-size distributions

1997 ◽  
Vol 43 (145) ◽  
pp. 473-479 ◽  
Author(s):  
Yi Chaolu
Keyword(s):  
Size Range ◽  
Coarse Fraction ◽  
The Other ◽  
Size Distributions ◽  
Thin Sections ◽  
Grain Sizes ◽  
Altay Mountains ◽  
Large Particles ◽  
Grain Size Distributions ◽  
Basal Till

AbstractQuartz, feldspar and chlorite, the principal minerals in a basal till from the Halasi River catchment in the Altay Mountains, northwestern China, are present in approximately equal concentrations in the coarse fraction of the till, 1.0-0.125 mm. Quartz concentrations are significantly higher than those of the other two minerals in the 0.125-0.016 mm size range. Feldspar and chlorite concentrations are higher than those of quartz in the finest fraction. Quartz has a strong preferred mode at 0.063-0.032 mm. Feldspar and chlorite have two weak modes in the silt-size range, one between 0.063 and 0.032 mm and the other between 0.016 and 0.004 mm.Thin sections of oriented impregnated samples were used to study crushing and abrasion. Over 2700 daughter particles were identified as products of comminution of 925 parent grains. Quartz and feldspar are most likely to be broken into two particles of roughly equal size, as are fine chlorite grains. However, owing to their weakness and cleavage, larger grains of chlorite tend to he split into more than two daughter particles.Sizes of the daughter grains were measured and sizes of the original parent grains were estimated. Mean parent grain-sizes for quartz, feldspar and chlorite are 0.129, 0.078 and 0.059 mm, respectively, whereas mean daughter grain-sizes are 0.068,0.041 and 0.024 mm, respectively. The greater percentage reduction in the size of chlorite reflects its tendency to break into more than two daughter particles.Most grains tend to be crushed. Only a few large particles seem to have suffered from abrasion.

Model-based closure experiments with optical particle counters for dust-like aerosols

2021 ◽  
Author(s):  
Josef Gasteiger ◽  
Adrian Walser ◽  
Maximilian Dollner ◽  
Marilena Teri ◽  
Bernadett Weinzierl
Keyword(s):  
Size Distribution ◽  
Size Range ◽  
Particle Orientation ◽  
Spherical Particles ◽  
Dust Particles ◽  
Optical Parameters ◽  
Size Distributions ◽  
Scattering Angle ◽  
Desert Dust ◽  
Shaped Particle

<div> <div></div> </div><div><!-- COMO-HTML-CONTENT-START --> <p>The size distribution of desert dust is a central parameter, e.g., for the dust climate effect and the fertilization of oceans and rain forests. The uncertainties of size distribution measurements, however, are large for which the nonsphericity of dust particles is a major reason. Optical particle counters (OPCs) are frequently used for size distribution measurements and possible reasons for uncertainties include (a) the fact that nonspherical dust particles fly with individual orientations through the sampling volume of the OPC while the scattering signals and derived sizes depend on particle orientation, (b) the variability of particle shape, and (c) uncertainties about which definition of particle size is best suited for nonspherical dust.</p> <p>To test the consistency between OPC measurements and independent measurements with other instruments types (e.g., a nephelometer or a lidar) closure experiments can be performed. In such experiments, size distributions derived from OPC measurements are used as input for model calculations of specific optical parameters which then are compared to independent measurements of the same optical parameters (e.g. scattering or backscattering coefficient) of the same aerosol. Deviations have been reported in the literature for desert dust. These deviations may be caused by the particle nonsphericity affecting the derivation of size distributions from OPC as indicated above but may also have other causes, e.g., using a wrong refractive index or assuming spherical particles for calculating the specific optical parameters. So far, the OPC nonsphericity effect has not been investigated in detail. A better understanding of this effect would be helpful for our understanding of size distribution uncertainties and of reasons for deviations in closure experiments.</p> <p>In order to gain insight into the OPC nonsphericity effect, we performed simulations for different combinations of OPCs and instruments measuring specific optical parameters. Irregular dust-like shapes over a wide size range and different refractive indices were considered. Firstly, the deviations of the derived sizes from the original particle sizes were analyzed. Secondly, the derived sizes were used for Mie simulations of the optical parameters and the deviations from those of the original irregularly-shaped particle were calculated. In this respect, e.g., nephelometer responses and lidar-relevant parameters were simulated to reproduce possible closure experiments. These results will be compared to measurement-based closure experiments performed during field campaigns or in a laboratory in order to investigate how well the OPC nonsphericity effect explains observed discrepancies.</p> <p>The simulated closure experiments show, for example, an overestimation of the scattering coefficient at λ=532nm by about 5% to 34% (depending on size range) when using size distributions derived from the DMT CAS instrument (λ=658nm, 4°-12° scattering angle) assuming non-absorbing dust particles. Using the TSI OPS model 3330 (λ=660nm, 30°-150° scattering angle) deviations in the range from -16% to +16% are found.</p> </div>

scholarly journals Subglacial comminution in till — evidence from microfabric studies and grain-size distributions

1997 ◽  
Vol 43 (145) ◽  
pp. 473-479 ◽  
Author(s):  
Yi Chaolu
Keyword(s):  
Size Range ◽  
Coarse Fraction ◽  
The Other ◽  
Size Distributions ◽  
Thin Sections ◽  
Grain Sizes ◽  
Altay Mountains ◽  
Large Particles ◽  
Grain Size Distributions ◽  
Basal Till

Abstract Quartz, feldspar and chlorite, the principal minerals in a basal till from the Halasi River catchment in the Altay Mountains, northwestern China, are present in approximately equal concentrations in the coarse fraction of the till, 1.0-0.125 mm. Quartz concentrations are significantly higher than those of the other two minerals in the 0.125-0.016 mm size range. Feldspar and chlorite concentrations are higher than those of quartz in the finest fraction. Quartz has a strong preferred mode at 0.063-0.032 mm. Feldspar and chlorite have two weak modes in the silt-size range, one between 0.063 and 0.032 mm and the other between 0.016 and 0.004 mm. Thin sections of oriented impregnated samples were used to study crushing and abrasion. Over 2700 daughter particles were identified as products of comminution of 925 parent grains. Quartz and feldspar are most likely to be broken into two particles of roughly equal size, as are fine chlorite grains. However, owing to their weakness and cleavage, larger grains of chlorite tend to he split into more than two daughter particles. Sizes of the daughter grains were measured and sizes of the original parent grains were estimated. Mean parent grain-sizes for quartz, feldspar and chlorite are 0.129, 0.078 and 0.059 mm, respectively, whereas mean daughter grain-sizes are 0.068,0.041 and 0.024 mm, respectively. The greater percentage reduction in the size of chlorite reflects its tendency to break into more than two daughter particles. Most grains tend to be crushed. Only a few large particles seem to have suffered from abrasion.

scholarly journals Experimental Results on Scattering by Irregular and Meteoritic Dust Particles Related to Photopolarimetry of Zodiacal Light and Comets

1985 ◽  
Vol 85 ◽  
pp. 223-226
Author(s):  
K. Weiss-Wrana ◽  
R.H. Giese ◽  
R.H. Zerull
Keyword(s):  
Light Scattering ◽  
Size Range ◽  
Experimental Results ◽  
Dust Particles ◽  
Dust Grains ◽  
Scattering Function ◽  
Negative Polarization ◽  
Zodiacal Light ◽  
Cometary Dust ◽  
Characteristic Features

AbstractThe investigations of light scattering by larger meteoritic and terrestrial single grains (size range 20 μm to 120 μm ) demonstrate that the scattering properties of irregularly shaped dark opaque particles with very rough surfaces resemble the characteristic features of the empirical scattering function as derived from measurements of the zodiacal light. Purely transparent or translucent irregularly shaped particles show a quite different scattering behaviour. Furthermore irregular and multicomponent fluffy particles in the size range of a few microns were modelled by microwave analog measurements in order to explain positive and negative polarization of the light scattered by cometary dust grains.

scholarly journals Observations of Saharan dust microphysical and optical properties from the Eastern Atlantic during NAMMA airborne field campaign

2011 ◽  
Vol 11 (2) ◽  
pp. 723-740 ◽  
Author(s):  
G. Chen ◽  
L. D. Ziemba ◽  
D. A. Chu ◽  
K. L. Thornhill ◽  
G. L. Schuster ◽  
...  
Keyword(s):  
Particle Size ◽  
Optical Properties ◽  
Dust Particle ◽  
Saharan Dust ◽  
Dust Particles ◽  
Small Range ◽  
Size Distributions ◽  
Particle Size Distributions ◽  
Field Campaign ◽  
Sahara Dust

Abstract. As part of the international project entitled "African Monsoon Multidisciplinary Analysis (AMMA)", NAMMA (NASA AMMA) aimed to gain a better understanding of the relationship between the African Easterly Waves (AEWs), the Sahara Air Layer (SAL), and tropical cyclogenesis. The NAMMA airborne field campaign was based out of the Cape Verde Islands during the peak of the hurricane season, i.e., August and September 2006. Multiple Sahara dust layers were sampled during 62 encounters in the eastern portion of the hurricane main development region, covering both the eastern North Atlantic Ocean and the western Saharan desert (i.e., 5–22° N and 10–35° W). The centers of these layers were located at altitudes between 1.5 and 3.3 km and the layer thickness ranged from 0.5 to 3 km. Detailed dust microphysical and optical properties were characterized using a suite of in-situ instruments aboard the NASA DC-8 that included a particle counter, an Ultra-High Sensitivity Aerosol Spectrometer, an Aerodynamic Particle Sizer, a nephelometer, and a Particle Soot Absorption Photometer. The NAAMA sampling inlet has a size cut (i.e., 50% transmission efficiency size) of approximately 4 μm in diameter for dust particles, which limits the representativeness of the NAMMA observational findings. The NAMMA dust observations showed relatively low particle number densities, ranging from 268 to 461 cm−3, but highly elevated volume density with an average at 45 μm3 cm−3. NAMMA dust particle size distributions can be well represented by tri-modal lognormal regressions. The estimated volume median diameter (VMD) is averaged at 2.1 μm with a small range of variation regardless of the vertical and geographical sampling locations. The Ångström Exponent assessments exhibited strong wavelength dependence for absorption but a weak one for scattering. The single scattering albedo was estimated at 0.97 ± 0.02. The imaginary part of the refractive index for Sahara dust was estimated at 0.0022, with a range from 0.0015 to 0.0044. Closure analysis showed that observed scattering coefficients are highly correlated with those calculated from spherical Mie-Theory and observed dust particle size distributions. These values are generally consistent with literature values reported from studies with similar particle sampling size range.

scholarly journals Laser ablation aerosol particle time-of-flight mass spectrometer (LAAPTOF): performance, reference spectra and classification of atmospheric samples

2018 ◽  
Vol 11 (4) ◽  
pp. 2325-2343 ◽  
Author(s):  
Xiaoli Shen ◽  
Ramakrishna Ramisetty ◽  
Claudia Mohr ◽  
Wei Huang ◽  
Thomas Leisner ◽  
...  
Keyword(s):  
Laser Ablation ◽  
Aerosol Particle ◽  
Mass Spectrometer ◽  
Size Range ◽  
Aerosol Particles ◽  
Time Of Flight ◽  
Polystyrene Latex ◽  
Dust Particles ◽  
Data Set ◽  
Flight Mass Spectrometer

Abstract. The laser ablation aerosol particle time-of-flight mass spectrometer (LAAPTOF, AeroMegt GmbH) is able to identify the chemical composition and mixing state of individual aerosol particles, and thus is a tool for elucidating their impacts on human health, visibility, ecosystem, and climate. The overall detection efficiency (ODE) of the instrument we use was determined to range from  ∼  (0.01 ± 0.01) to  ∼  (4.23 ± 2.36) % for polystyrene latex (PSL) in the size range of 200 to 2000 nm,  ∼  (0.44 ± 0.19) to  ∼  (6.57 ± 2.38) % for ammonium nitrate (NH4NO3), and  ∼  (0.14 ± 0.02) to  ∼  (1.46 ± 0.08) % for sodium chloride (NaCl) particles in the size range of 300 to 1000 nm. Reference mass spectra of 32 different particle types relevant for atmospheric aerosol (e.g. pure compounds NH4NO3, K2SO4, NaCl, oxalic acid, pinic acid, and pinonic acid; internal mixtures of e.g. salts, secondary organic aerosol, and metallic core–organic shell particles; more complex particles such as soot and dust particles) were determined. Our results show that internally mixed aerosol particles can result in spectra with new clusters of ions, rather than simply a combination of the spectra from the single components. An exemplary 1-day ambient data set was analysed by both classical fuzzy clustering and a reference-spectra-based classification method. Resulting identified particle types were generally well correlated. We show how a combination of both methods can greatly improve the interpretation of single-particle data in field measurements.

scholarly journals Coarse and giant particles are ubiquitous in Saharan dust export regions and are radiatively significant over the Sahara

2020 ◽  
Author(s):  
Claire Ryder ◽  
Eleanor Highwood ◽  
Adrian Walser ◽  
Petra Walser ◽  
Anne Philipp ◽  
...  
Keyword(s):  
Mass Concentration ◽  
Size Range ◽  
State Of The Art ◽  
Chem Phys ◽  
Saharan Dust ◽  
Dust Particles ◽  
Field Campaign ◽  
Dust Transport ◽  
Coarse Mode ◽  
Significant Underestimation

<p>Mineral dust is an important component of the climate system, interacting with radiation, clouds, and biogeochemical systems and impacting atmospheric circulation, air quality, aviation, and solar energy generation. These impacts are sensitive to dust particle size distribution (PSD), yet models struggle or even fail to represent coarse (diameter (<span><em>d</em></span>) <span>>2.5</span> <span>µ</span>m) and giant (<span><em>d</em>>20</span> <span>µ</span>m) dust particles and the evolution of the PSD with transport. Here we examine three state-of-the-art airborne observational datasets, all of which measured the full size range of dust (<span><em>d</em>=0.1</span> to <span>>100</span> <span>µ</span>m) at different stages during transport with consistent instrumentation. We quantify the presence and evolution of coarse and giant particles and their contribution to optical properties using airborne observations over the Sahara (from the Fennec field campaign) and in the Saharan Air Layer (SAL) over the tropical eastern Atlantic (from the AER-D field campaign).</p><p>Observations show significantly more abundant coarse and giant dust particles over the Sahara compared to the SAL: effective diameters of up to 20 <span>µ</span>m were observed over the Sahara compared to 4 <span>µ</span>m in the SAL. Excluding giant particles over the Sahara results in significant underestimation of mass concentration (40 %), as well as underestimates of both shortwave and longwave extinction (18 % and 26 %, respectively, from scattering calculations), while the effects in the SAL are smaller but non-negligible. The larger impact on longwave extinction compared to shortwave implies a bias towards a radiative cooling effect in dust models, which typically exclude giant particles and underestimate coarse-mode concentrations.</p><p>A compilation of the new and published effective diameters against dust age since uplift time suggests that two regimes of dust transport exist. During the initial 1.5 d, both coarse and giant particles are rapidly deposited. During the subsequent 1.5 to 10 d, PSD barely changes with transport, and the coarse mode is retained to a much greater degree than expected from estimates of gravitational sedimentation alone. The reasons for this are unclear and warrant further investigation in order to improve dust transport schemes and the associated radiative effects of coarse and giant particles in models.</p><p>This work has been recently published in ACP (Ryder, C. L., Highwood, E. J., Walser, A., Seibert, P., Philipp, A., and Weinzierl, B.: Coarse and giant particles are ubiquitous in Saharan dust export regions and are radiatively significant over the Sahara, Atmos. Chem. Phys., 19, 15353–15376, https://doi.org/10.5194/acp-19-15353-2019, 2019).</p>

scholarly journals Atmospheric radiative effects of an in-situ measured Saharan dust plume and the role of large particles

2007 ◽  
Vol 7 (3) ◽  
pp. 7767-7817 ◽  
Author(s):  
S. Otto ◽  
M. de Reus ◽  
T. Trautmann ◽  
A. Thomas ◽  
M. Wendisch ◽  
...  
Keyword(s):  
Complex Refractive Index ◽  
Single Scattering ◽  
Single Scattering Albedo ◽  
Saharan Dust ◽  
Dust Particles ◽  
Modal Parameters ◽  
Size Distributions ◽  
Radiative Effects ◽  
Enhanced Absorption ◽  
Large Particles

Abstract. This work will present aerosol size distributions measured in a Saharan dust plume between 0.9 and 12 km altitude during the ACE-2 campaign 1997. The distributions contain a significant fraction of large particles of diameters from 4 to 30 μm. Radiative transfer calculations have been performed using these data as input. Shortwave, longwave as well as total atmospheric radiative effects (AREs) of the dust plume are investigated over ocean and desert within the scope of sensitivity studies considering varied input parameters like solar zenith angle, scaled total dust optical depth, tropospheric standard aerosol profiles and particle complex refractive index. The results indicate that the large particle fraction has a predominant impact on the optical properties of the dust. A single scattering albedo of ωo=0.75–0.96 at 550 nm was simulated in the entire dust column as well as 0.76 within the Saharan dust layer at ~4 km altitude indicating enhanced absorption. The measured dust leads to cooling over the ocean but warming over the desert due to differences in their spectral surface albedo and surface temperature. The large particles absorb strongly and they contribute at least 20% to the ARE in the dusty atmosphere. From the measured size distributions modal parameters of a bimodal lognormal column volume size distribution were deduced, resulting in a coarse median diameter of ~9 μm and a column single scattering albedo of 0.78 at 550 nm. A sensitivity study demonstrates that variabilities in the modal parameters can cause completely different AREs and emphasises the warming effect of the large mineral dust particles.

Seasonal size distributions of suspended solids in a stormwater management pond

1999 ◽  
Vol 39 (2) ◽  
pp. 127-134 ◽  
Author(s):  
B. G. Krishnappan ◽  
J. Marsalek ◽  
W. E. Watt ◽  
B. C. Anderson
Keyword(s):  
Particle Size ◽  
Water Samples ◽  
Stormwater Management ◽  
Suspended Solids ◽  
Size Range ◽  
Empirical Relationship ◽  
Size Distributions ◽  
Fall Velocity ◽  
Floc Size ◽  
Primary Particles

Three seasonal surveys of suspended solids were carried out in an on-stream stormwater management pond, by means of a submersible laser particle size analyser. Size distributions were measured at up to 17 points in the pond, and water samples collected at the same locations were analysed for primary particles aggregated in flocs. Observed suspended solids were mostly composed of flocs, with maximum sizes ranging from 30 to 212 μm for winter and summer surveys, respectively. Using a relationship defining the floc density as a function of floc size and Stokes' equation for settling, an empirical relationship expressing the floc fall velocity as a function of floc size was produced. This relationship indicates that naturally formed flocs in the size range from 5 to 15 μm would settle faster than both smaller primary particles of higher density, and somewhat larger flocs of lower density, which are however susceptible to break up by turbulence.

scholarly journals Estimating the Asteroidal Component of the Zodiacal Cloud using the Earth's Resonant Ring

1996 ◽  
Vol 150 ◽  
pp. 155-158 ◽  
Author(s):  
Sumita Jayaraman ◽  
Stanley F. Dermott
Keyword(s):  
Surface Area ◽  
Frequency Distribution ◽  
Size Range ◽  
Dust Cloud ◽  
Dust Particles ◽  
Direct Function ◽  
Size Frequency Distribution ◽  
Limited Size ◽  
Zodiacal Cloud ◽  
Asteroidal Dust

AbstractThe Earth's resonant ring is populated primarily by asteroidal dust particles because cometary particles have higher Poynting-Robertson drag rates and the Earth's resonances are not strong enough to trap them (Gomes, 1995). It has been shown that asteroidal particles in a limited size range from 5 — 30μm are responsible for the observed trailing/leading flux asymmetry caused by the trailing dust cloud embedded in the ring (Jayaraman and Dermott 1995). The magnitude of the flux asymmetry is a direct function of the area of dust in the ring, which in turn depends upon the number of asteroidal particles in the zodiacal cloud. Using a dynamical model of the ring and the background zodiacal cloud and estimating the surface area of dust needed in the ring to match the observed flux asymmetry in the 25 micron COBE waveband, we have calculated the fraction of asteroidal dust in the zodiacal cloud as a function of p, the slope of the size-frequency distribution of particles.

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