Dusty Atmosphere Research Articles

A study of the influence of the surface emittance and extinction by dust on Martian IR spectra

The main issue in the interpretation of the measured Martian spectra is how to discriminate between surface and atmospheric contribution to the spectral features. A review of this problem is given in this paper. Moreover, some examples of spectra simulated with radiative transfer programs which take into account the cumulative effect of a surface and an atmosphere containing gases and dust are shown. Various states of the dusty atmosphere and of the surface of Mars have been taken into consideration. The studies presented here are directly connected with spectrometric measurements to be carried during the present (Thermal Emission Spectrometer aboard the Mars Global Surveyor) and future (Planetary Fourier Spectrometer aboard Mars Express) missions to Mars.

Late Pleistocene Climatic Variations at Achenheim, France, Based on a Magnetic Susceptibility and TL Chronology of Loess

New field investigations of the Achenheim sequence (Alsace, France) allow for the characterization of variations in the low-field magnetic susceptibility over most of the last climatic cycle, i.e., the past 130,000 yr. New stratigraphic data and thermoluminescence measurements permit reassessment of the previous chronological interpretation of the Upper Pleistocene at Achenheim. A high-resolution analysis of magnetic susceptibility discloses the occurrence of a fine-grained “marker” horizon which was also found recently in another section. This horizon is interpreted as a small-scale dust layer deposited prior to the main interval of loess deposition. The horizon, deposited at the marine isotope stage (MIS) 5/4 boundary, has been found in other loess sequences and is especially prevalent in central Europe. It is characterized by low susceptibility values and a grayish color. New thermoluminescence dates indicate that the loess deposition took place after the MIS 5/4 boundary, i.e., after 70,000 yr. These results are consistent with the Greenland GRIP ice-core dust record which also demonstrates a dusty atmosphere after 72,000 yr ago. On a more regional scale, the Achenheim loess sequence demonstrates a reliable correlation between the western side of the Eurasian loess belt and the dust record of the Greenland ice cores.

The Mars Pathfinder Atmospheric Structure Investigation/Meteorology (ASI/MET) Experiment

The Mars Pathfinder atmospheric structure investigation/meteorology (ASI/MET) experiment measured the vertical density, pressure, and temperature structure of the martian atmosphere from the surface to 160 km, and monitored surface meteorology and climate for 83 sols (1 sol = 1 martian day = 24.7 hours). The atmospheric structure and the weather record are similar to those observed by the Viking 1 lander (VL-1) at the same latitude, altitude, and season 21 years ago, but there are differences related to diurnal effects and the surface properties of the landing site. These include a cold nighttime upper atmosphere; atmospheric temperatures that are 10 to 12 degrees kelvin warmer near the surface; light slope-controlled winds; and dust devils, identified by their pressure, wind, and temperature signatures. The results are consistent with the warm, moderately dusty atmosphere seen by VL-1.

Adaptive Optics Infrared Imaging Polarimetry and OpticalHSTImaging of Hubble's Variable Nebula (R Monocerotis/NGC 2261): A Close Look at a Very Young Active Herbig Ae/Be star

We present high-resolution (FWHM = 02) near-IR (J, H, and K') adaptive optics images of the Herbig Ae/Be star R Monocerotis. Optical Hubble Space Telescope (HST) WFPC2 PC camera archival images are also presented. For the first time, adaptive optics was utilized to make high-resolution (FWHM = 02) IR-imaging polarimetry maps of R Mon. In addition, the first mid-IR array images (at 11.7 and 20.8 ?m) of R Mon have been obtained. We also present new 3.16, 3.93, and 4.67 ?m images. We have found that R Mon is a 069 binary star with a companion that dereddens onto the classical T Tauri locus. Based on the near-infrared photometry of this companion we believe it is a 1.5 M?, very young ( + 800?280 pc distant based on previous proper-motion and radial velocity measurements of R Mon's jet. Our high-resolution (FWHM ~ 02) adaptive optics infrared polarimetry maps agree with the current interpretation that NGC 2261 is a reflection nebula illuminated by R Mon. Interior to the parabolic shell there is a complex of twisted filaments along the eastern edge. These filaments resemble a double-helical structure which is well described by a power law from ~103 to 105 AU from R Mon. This double helix may trace a twisted magnetic field above R Mon. Based on H I emission-line ratios, we find the direct extinction toward R Mon to be AV = 13.1 mag in the infrared (? > 1.28 ?m), falling to a lower value of AV = 3.6 mag in the optical (? < 1.28 ?m), where scattered light increasingly lowers the effective extinction in the line ratios. The large AV = 13.1 extinction is likely due to the dusty atmosphere of an inclined R ~ 100 AU optically thick accretion disk surrounding R Mon. A simple model of such an accretion disk + star system (with Macc ~ 8 ? 10-5 M? yr-1, M* = 10.4 M?, R* = 2 R?, and T* ~ 3.5 ? 104 K) reproduces the observed dereddened R Mon spectral energy distribution (SED) from the optical (0.4 ?m) to the millimeter region. Consideration of the lower extinction (AV = 3.6) on the path followed by the scattered visible light eliminated any need for an inner gap in the accretion disk model to reproduce the SED. In general, young stellar objects (YSOs) that are obscured in the optical but directly visible in the infrared will have different effective optical and infrared extinctions. Infrared extinctions derived from optical observations dominated by scattered light will be underestimates of the true IR extinction along the direct path. The use of an independent estimator of both the optical and infrared extinctions such as common upper-level H I recombination lines is highly desirable. The utilization of the correct optical and infrared extinctions may relieve the need for optically thin inner-disk gaps to explain YSO near-IR SEDs.

Numerical simulation of the interaction of dust particles of a comet with a spacecraft

The paper deals with the physical and mathematical statement of problems that arise in estimating the safety of the shield design of the “Vega” spacecraft, which was chosen preliminarily under the guidance of R. Z. Sagdeev. Numerical results for failure of shields impacted by particles of the dusty atmosphere of Halley's comet are presented. The size of the failure zones in the shields are determined as a function of the particle size and density. The probability of an impact on the second shield of the particles penetrating the shield or resulting in spalling of solid fragments is estimated. The momentum transmitted by the particle flux to the solar batteries of the spacecraft is determined.

Meridional Transport and Water Reservoirs in Southern Mars during 1988-1989

Latitudinally resolved measurements of water-vapor column abundance in the martian atmosphere, obtained on four occasions in 1988-1989, are analyzed by a two-dimensional (2D) zonally symmetric water transport model. It predicted no substantial meridional water-vapor transport during the period covered by the observations. If the fundamental assumption of the model holds—that the mean meridional (overturning cell) and CO2 condensation/sublimation flows transport most of the water during this time of the martian year—then the southern midlatitudes are strongly indicated as the sink for the water that disappeared during this period. The model predicts the chances of the southern residual cap being the source of large amounts of water vapor during southern summer to be low. It also predicts that a very dusty atmosphere would have enhanced the transport of water vapor to the north during this season.

Atmospheric effects on the mapping of Martian thermal inertia and thermally derived albedo

We examine the effects of a dusty CO2 atmosphere on the thermal inertia and thermally derived albedo of Mars and we present a new map of thermal inertias. This new map was produced using a coupled surface atmosphere (CSA) model, dust opacities from Viking infrared thermal mapper (IRTM) data, and CO2 columns based on topography. The CSA model thermal inertias are smaller than the 2% model thermal inertias, with the difference largest at large thermal inertia. Although the difference between the thermal inertias obtained with the two models is moderate for much of the region studied, it is largest in regions of either high dust opacity or of topographic lows, including the Viking Lander 1 site and some geologically interesting regions. The CSA model thermally derived albedos do not accurately predict the IRTM measured albedos and are very similar to the thermally derived albedos obtained with models making the 2% assumption.

Principles for formulating theory of condition for lubricating oils under service conditions

Indexes of oil condition, with certain exceptions, are regulated by standardization documents and various types of instructions for operation; indexes (criteria) of reliability stem from the corresponding theory. A special problem is represented by the form and method of generalizing oil condition indexes for subsequent comparison with reliability criteria of the object or parameters that are proportional to these criteria. In a particular, special case, such a comparison is simplified by singling out the dominant process taking place in the oil that has an adverse effect on the reliability of the object, or by singling out the least reliable element in the construction of the object, sharply different from the others, the behavior of which is closely related to changes in quality of the oil that is used. The set of indexes may also change under specific conditions of equipment operation, for example in a dusty atmosphere, when large amounts of dust and other solid products enter the oil and may reduce the reliability of the object as a consequence of increased abrasive wear of mating parts. In this case, the most informative index is the oil's content of particulate contaminant, in particular its silicon content. Moreover, certain components and parts of vehicles and mechanisms, because of their particular design features, are less reliable in comparison with the other parts, particularly in contact with the working oil. An example may be found in parts made of leaded bronze, which i s particularly subject to corrosive-mechanical wear in the course of operation. In these cases, in the oil and in the object itself, particular attention is given to monitoring the metal content of the oil and the weight loss or change in dimensions of the corresponding parts; determination of the other indexes may be optional.

Investigation of optical and radiative properties of atmospheric dust aerosols

Abstract A dust aerosol optical model is proposed as a result of analysis of the data obtained during the U.S.S.R.-U.S. experiment in Tadzhikistan, 1989. The model consists of spectral dependencies of the single scattering albedo, ω, the asymmetry parameter of the scattering phase function, g, and of possible values of the aerosol optical thickness, τ, for background conditions and for dust storms. This model and available published optical models of dust aerosols were used to perform simulations of radiative forcing in the dusty atmosphere. Results obtained are compared with corresponding results for Saharan aerosol. It is shown that atmospheric dust strongly decreases the total radiative balance of the underlying surface and at the same time induces general warming of the underlying surface-atmosphere system due to a decrease in the system albedo over the arid zones. The calculated heating/cooling rates in the atmosphere are analysed together with data from aerological soundings and radiation measurements.

Heatshield erosion in a dusty Martian atmosphere

The study calculates the effects of dust particle impacts on the erosion of the forebody heat shield for a 26-m diameter aerobraking vehicle entering the Martian atmosphere at 8.6 km/s. An explicit thin-layer Navier-Stokes code is used to compute the dustless flowfield about the vehicle for the actual Martian atmospheric composition. The deceleration and melting of the dust particles within the forebody shock layer was computed for dust spherules having initial diameters from 1 to 19 microns. All the particles began vaporizing shortly after entering the shock layer, but most survived to hit the heat shield surface. The two different heat shield materials considered were Shuttle ceramic tiles with glassy surfaces and a moderate-density ablator. For a vehicle with a ballistic coefficient of 200 kg/sq m, a glassy heat shield surface experienced an average of 7 mm of surface erosion, or 20 times the thickness of the glassy layer on ceramic tiles.

Millimeter-wave radio scattering from discharges stimulated by a laser pulse in the dusty atmosphere

Millimeter-wave radio scattering from discharges stimulated by a laser pulse in the dusty atmosphere

Multidimensional Dusty Gasdynamical Models of Inner Cometary Atmospheres

Abstract.The presently available multidimensional dusty gasdynamic cometary atmosphere models are reviewed. This paper examines the simplifying assumptions and their potential consequences. Special attention is paid to the question of potential nightside dust accumulation presently predicted by Korosmezey and Gombosi (1989).

Modeling of the cometary nucleus-coma interface region

A well-developed dusty cometary atmosphere extends to distances over 4 orders of magnitude larger than the size of the nucleus. Pre-encounter models of the inner coma were based on the assumption that a spherically symmetric description was adequate to describe the dust-gas interaction region. Recent observational evidence together with a new generation of multidimensional theoretical models demonstrate that the inner cometary environment is far from spherical symmetry and a number of unexpected phenomena (dust jet broadening, subsolar dust spike formation, etc.) might play a significant role in this region.

Zonally Symmetric Response to Atmospheric Tidal Forcing in the Dusty Martian Atmosphere

The paper presents a steady state, zonally symmetric response of an atmospheric circulation to the combined effects of the very large zonal-mean diabatic heating and thermotidal forcing thought to exist in the dusty Martian atmosphere during one of its episodic global dust storms. The zonal-mean components of the tidal flux-convergences of momentum and heat are computed using an existing classical atmospheric tidal model constrained by the surface pressure observations at the two Viking Lander sites on Mars. A nearly inviscid two-dimensional model is used to compute the zonally symmetric response to the computed tidal flux-convergences and to the zonal-mean heating of the airborne dust. The results are compared with data from the Viking missions.

Infrared heating of Comet Halleys atmosphere

The warm circumnuclear dust in the inner cometary coma reradiates in the IR in the wavelength range of the ground state rotational band of the dominant atmospheric molecule, H2O. However, the interaction of this radiation with H2O has hitherto not been taken into account in cometary atmospheric models. Here we have extended our earlier two-phase, multifluid model of the dusty atmosphere by including this effect. Although this IR radiation initially pumps the rotational levels of H2O, frequent intermolecular collisions in the inner coma transfer this energy from rotational modes to translational modes. As a result the temperature in the innermost coma no longer decreases to about 10 K, as predicted by the earlier models, but reaches a minimum of only about 120 K.

Laboratory evaluation of RDM-201 Respirable Dust Monitor.

The current paper discusses the results of laboratory experiments conducted to evaluate the GCA Respirable Dust Monitor RDM-201 in comparison with the standard Gravimetric Respirable Dust Sampler (GRDS). The samplers were compared in parallel within the atmosphere of an inhalation chamber laden with Arizona Fine Road Dust (AFRD). A wide range of dust concentrations (i.e., from 0.17 to 32:81 mg/m3) was used in the experiments. Sampling time varied from 15 to 120 min. There was a high agreement between the two GRDSs, particularly for samples with dust weight larger than 0.5 mg. The correlation and linearity between the RDM-201 display reading and the actual weight of dust on the instrument's filter were quite high for dust samples larger than 0.5 mg, but dropped significantly for samples less than 0.5 mg. Considering the extremely high dust concentration required to collect a minimum of 0.5 mg of respirable dust within 1-min sampling time of the RDM-201's automatic sampling mode, it was concluded that the use of automatic mode intended for quick evaluation of dusty atmosphere is impractical under most ordinary dusty conditions. The RDM-201 manual mode can be used, however, as reliably as a GRDS, for extended sampling times for assessment of TWAC of respirable dust in the atmosphere of a workplace, providing that a minimum of 0.5 mg sample is collected on the filter.

Atmospheric Tidal Forcing of the Zonal-Mean Circulation: The Martian Dusty Atmosphere

Classical atmospheric tidal theory has been used to compute the bilinear tidal zonal-mean forcing per unit mass of the zonal-mean meridional and zonal winds, together with the tidal zonal-mean heating per unit mass for the dusty Martian atmosphere. The convergences of the tidal Eliassen-Palm (EP) flux have been computed for both clear and dusty atmospheric conditions, including the special case of a 'dusty corridor' in the summer southern subtropics that is meant to simulate the early stages of a planetary-scale Martian dust storm. The calculation of the tidal EP zonal forcing differs from Hamilton in that more realistic thermotidal forcings and basic state temperatures are used. The zonal-mean convergences of the tidal fluxes of heat and momentum are large during a Martian great dust storm and should alter significantly the zonal-mean circulation and its residual component driven by the zonal-mean heating. In particular, the tidal forcing of the meridional wind, which is an order of magnitude greater than its zonal counterpart, is likely to give rise to a complex pattern of significantly ageostrophic zonal-mean flow in the Martian tropics.

Boundary layer on a blunt body in a flow of dusty gas

The problem of interaction of gas-dust flows with solid surfaces arose in connection with the study of the motion of aircraft in a dusty atmosphere [1–2], the motion of a gas suspension in power generators, and in a number of other applications [3]. The presence of a disperse admixture may lead to a significant increase in the heat fluxes [4] and to erosion of the surface [5]. These phenomena are due to the joint influence of several factors — the change in the structure of the carrier-phase boundary layer due to the presence of the particles, collisions of the particles with the surface, roughness of the ablating surface, and so forth. This paper continues an investigation begun earlier [6–7] into the influence of particles on the structure of the dynamical and thermal two-phase boundary layer formed around a blunt body in a flow. The model of the dusty gas [8] has an incompressible carrier phase. The method of matched asymptotic expansions [9] is used to obtain the equations of the two-phase boundary layer. In the frame-work of the refined classification made by Stulov [6], it is shown that the form of the boundary layer equations is different in the presence and absence of inertial precipitation of the particles. The equations are solved numerically in the neighborhood of the stagnation point of the blunt body. The temperature and phase velocity distributions in the boundary layer, and also the friction coefficients and the heat transfer of the carrier phase are found for a wide range of the determining parameters. In the case of an admixture of low-inertia particles that are not precipitated on the body, it is shown that even when the mass concentration of the particles in the undisturbed flow is small their accumulation in the boundary layer can lead to a sharp increase in the thermal fluxes at the stagnation point.

The effects of the diffuse radiation fields due to multiple scattering and thermal reradiation by dust on the dynamics and thermodynamics of a dusty cometary atmosphere

A self-consistent model of a dirty, clathrate cometary nucleus is extended to account for diffuse radiation fields caused by multiple scattering and thermal reradiation of the solar continuum by dust. The model is configured to fit conditions expected for the various spacecraft which will encounter Halley's comet at 0.89 AU. The atmosphere is assumed a chemically reactive dust-gas mixture in quasi-steady spherically symmetric expansion. The effect of electron-neutral ion collisions is accounted for, along with rate constants of the various species of clathrate ice particles and radiative transfer of the solar input in the UV, visible and near-IR intervals. The opacity of the circumnuclear dust is projected to be an order of magnitude greater than previous estimates, which severely impacts the potential visibility of the nucleus to the cameras of the flyby satellites.

Passage of pulse radiation through a dusty atmosphere under conditions of development of breakdown on the particles

Passage of pulse radiation through a dusty atmosphere under conditions of development of breakdown on the particles