Light scattering by an optically thin inhomogeneous spherically symmetric planetary atmosphere

An approximate solution has been obtained for the problem of multiple scattering of light in an optically thin, inhomogeneous spherically symmetric planetary atmosphere illuminated by parallel solar radiation. A three-stream division of the radiation field has been made and a generalized Eddington approximation developed to solve the moment equations of the problem.     

Light scattering by an optically thin inhomogeneous,spherically-symmetric planetary atmosphere: Brightness at the zenith near the terminator

The approximate method of representing the intensity by a three-stream angular division is used to compute the brightness at the zenith near the terminator of an optically thin, spherically-symmetric planetary atmosphere illuminated by parallel solar radiation. The results are compared with those of Sobolev obtained under classical Eddington approximation.Part of this work was done when the author was on sabbatical leave at Kanazawa Institute of Technology (Japan).     

Direct statistical simulation of the near-surface layers of a cometary atmosphere. II: A nonspherical nucleus

The study presents the results of numerical simulations of mass-transfer processes in the near-surface layer of the cometary nucleus and in the inner part of the cometary atmosphere, which is formed under the action of solar radiation. The gas-kinetic model of the inner part of the cometary atmosphere surrounding a spherical nucleus (Skorov et al., 2004) is extended to the case of a nonspherical nucleus with axial symmetry. After high-resolution images of comets 19P/Borrelly and Wild 2 have been obtained by Deep Space 1 and Stardust spacecraft, such an extension seems to be vital and important. The nucleus and the inner part of the coma are closely related to each other because of the permanent exchange of energy and mass; therefore, they are modeled consistently. As in the first part of our study, the boundary conditions at the inner boundary of the simulation domain, which are necessary for gas-kinetic simulations, were determined from the self-consistent model of heat and mass transfer in a porous cometary nucleus that was developed earlier by the authors. The model took into account the volumetric character of the radiation absorption in a porous sublimating medium, the kinetic regime of the transport of sublimation products in the pores, and the backward gas fluxes from the coma due to intermolecular collisions. We considered different models of the nucleus structure that determined the effective gas production. Using the direct simulation Monte Carlo method, we computed the two-dimensional gas flow from a heterogeneous nonspherical cometary nucleus. The simulations were performed using the SMILE software. The parallel computer implementation of the software made it possible to calculate the spatial structure of the gas flow for the entire circumnucleus zone.     

Solar flux in Saturn's atmosphere: Penetration and heating rates in the aerosol and cloud layers

In this work, we describe an analysis of the internal solar radiation fields in Saturn's atmosphere. The aim of this paper is to study how the solar radiation flux in optical wavelengths (0.25-1.0 μm) is attenuated, primarily by the effect of the aerosols located close to the tropopause level, retrieving also the corresponding solar heating rates. We use a doubling-adding method and previous results on the vertical cloud and haze structure of Saturn's atmosphere. Our study shows that the maximum penetration level (∼250 mbar) for these wavelengths is substantially higher than previously expected because of the huge optical thickness of the tropospheric haze described in all vertical cloud structure models. We compare our results with previous estimates and parameterizations for seasonal climate models and propose a new approach for future models, with an intense and concentrated heating rate close to the top level of the tropospheric haze. Given that our spectral range accounts for about the 70% of the total solar flux, and using previous estimates for the penetration levels of infrared radiation in Saturn's atmosphere, we conclude solar radiation effect is negligible at levels below 600 mbar. This result is fundamental for understanding the role of solar radiation in the general atmospheric circulation of Saturn.     

Light Deflection Near the Sun's Limb: Refraction by the Solar Atmosphere

Light refraction by the Sun's atmosphere is calculated.As detected from the Earth, the refraction can deflect a light ray emitted from the Sun's limb by 13 or a starlight ray grazing the solar limb by 26, an effect 15 times larger than the gravitational deflection.     

Solution of the equation of transfer for coherent scattering in an exponential atmosphere by Busbridge's method

A solution of the transfer equation for coherent scattering in stellar atmosphere with Planck's function as a nonlinear function of optical depth, viz. $$B{\text{ }}_v (T) = b_0 + b_1 {\text{ }}e^{ - \beta \tau } $$ is obtained by the method developed by Busbridge (1953).     

Solution of the equation of transfer for coherent scattering in an exponential atmosphere by Eddington's method

An approximate solution of the transfer equation for coherent scattering in stellar atmospheres with Planck's function as a nonlinear function of optical depth, viz., $$B_v \left( T \right) = b_0 + b_1 e^{ - \beta \tau } $$ is obtained by Eddington's method. is obtained by Eddington's method.     

Influence of the interplanetary magnetic field on cometary and primordial dust orbits: Applications of Lorentz scattering

The equations describing the change in orbital elements of interplanetary dust due to Lorentz-force accelerations are presented in a simplified form. Such accelerations depend on the charge state of the dust; results of theoretical calculations for five possible dust materials are presented. Under present-day conditions, it is possible that semiconducting material such as graphite might carry a net voltage near zero, compared with a roughly 10-V charge expected for other grains. The scattering of dust by a randomly changing magnetic field can be viewed analogously to the dust diffusing in space; the equations presented thus can be used to interpret observations of the present distribution of dust in terms of its possible sources and sinks. The stronger magnetic fields of the early solar system would have led to more vigorous scattering of the dust; particles as large as 1 mm could have been significantly transported by Lorentz scattering during this time.     

Solar flare track densities in interplanetary dust particles: The determination of an asteroidal versus cometary source of the zodiacal dust cloud

Dust particles that are larger than 1 μm, when injected into the Solar System from comets and asteroids, will spiral into the Sun due to the Poynting-Robertson effect. During the process of spiraling in, such dust particles accumulate solar flare tracks in their component minerals. The accumulated track density for a given dust grain is a function of the duration of its space exposure and its distance from the Sun. Using a computer model, it was determined that the expected track density distributions from grains produced by comets are very different from those produced by asteroids. Individual asteroids produce populations of particles that arrive at 1 AU with scaled track density distributions containing “spikes,” while comets supply particles with a flatter and wider distribution of track densities. Particles with track densities above 3 × 10⁷ (sϱA/v) tracks/cm² have probably been exposed to solar flare tracks prior to injection into the interplanetary medium and are therefore likely to be asteroidal. Particles with track densities below 0.7 × 10⁷(sϱA/v) tracks/cm² must be derived from comets or Earth-crossing asteroids. Earth-crossing asteroids are not responsible for all the dust collected at 1 AU since they cannot produce the large track densities observed in some of the interplanetary dust particles collected in the stratosphere. The track densities observed in the stratospheric dust fall within the predicted range, but there is at present an insufficient number of carefully determined densities to make strong statements about the sources of the present dust population.     

Evolution of the Martian atmosphere and hydrosphere: Solar wind erosion studied by ASPERA-3 on Mars Express

The evolution of the Martian atmosphere and the potential existence of a past hydrosphere is a scientific issue of great interest in planetary research. Although the first missions to Mars had a focus on surface features and atmospheric properties, some of the missions (e.g., The Soviet Mars 2, 3 and 5) also carried instruments addressing the solar wind interaction with the Martian atmosphere and ionosphere and the potential existence of an intrinsic magnetic field on Mars. However, it took until 1989 before a spacecraft, Phobos-2, was able to carry out a more detailed investigation of the solar wind interaction with Mars. Phobos-2 gave valuable data on the Solar wind interaction with Mars during about 2 months of operations, leading to a better understanding of the solar wind impact on a weakly magnetized planet. However, Phobos-2 also raised a number of critical issues that has left science without adequate data since 1989.Investigations planned for Mars Express will cast new light on important aspects of the solar wind interaction with Mars. ASPERA-3 (Analyzer of Space Plasma and Energetic Atoms) on Mars Express will focus on the overall plasma outflow and monitor remotely the outflow and inflow of energetic neutral atoms produced by charge exchange processes. This report will discuss some of the unsolved issues about the solar wind interaction with Mars and how we plan to address these issues with Mars Express.     

Solution of the equation of transfer for coherent scattering in an exponential atmosphere by the method of discrete ordinates

A solution of the transfer equation for coherent scattering in stellar atmosphere with Planck's function as a nonlinear function of optical depth, viz., $$B_v (T) = b_0 + b_1 {\text{ }}e^{ - \beta \tau } $$ is obtained by the method of discrete ordinates originally due to Chandrasekhar.     

What can we expect from the in situ chemical investigation of a cometary nucleus by gas chromatography: First results from laboratory studies

Comets are probably the most primitive bodies of the solar system, and they participated in the early bombardment of the primitive planets. Consequently, the knowledge of their composition can play a key role in our understanding of the solar system formation, the origin of the planetary volatile constituents, and the origin of the organics implied in terrestrial prebiotic chemistry. However, we still do not have any direct information about the molecular composition of the cometary nucleus. This is why the COmetary SAmpling and Composition experiment (COSAC), onboard the surface landing probe of the Rosetta cometary mission, is specifically devoted to the molecular and enantiomeric analysis of a cometary nucleus. This experiment includes a gas chromatograph instrument dedicated to the specific identification and quantification of the general molecular species present in samples collected at the nucleus surface. In order to evaluate the performances of the integrated chromatographic system which was selected for the flight model instrument, experiments were carried out with a laboratory set up that reproduced the flight configuration and mimicked the in situ operating conditions. The obtained results demonstrate the ability for the gas chromatograph to identify a wide range of organic and inorganic volatile compounds, even those present at trace level, within the constrained space operating conditions. The aim of this paper is to present, for the first time, the performances of this system and to discuss the potential role of in situ gas chromatographic measurements in the future cometary, planetological and prebiotic chemistry studies.     

Light scattering by complex particles in the Moon's exosphere: Toward a taxonomy of models for the realistic simulation of the scattering behavior of lunar dust

It is suspected that the lunar exosphere has a dusty component dispersed above the surface by various physical mechanisms. Most of the evidence for this phenomenon comes from observations of “lunar horizon glow” (LHG), which is thought to be produced by the scattering of sunlight by this exospheric dust. The characterization of exospheric dust populations at the Moon is key to furthering our understanding of fundamental surface processes, as well as a necessary requirement for the planning of future robotic and human exploration.We present a model to simulate the scattering of sunlight by complex lunar dust grains (i.e. grains that are non-spherical and can be inhomogeneous in composition) to be used in the interpretation of remote sensing data from current and future lunar missions. We numerically model lunar dust grains with several different morphologies and compositions and compute their individual scattering signatures using the Discrete Dipole Approximation (DDA). These scattering properties are then used in a radiative transfer code to simulate the light scattering due to a dust size distribution, as would likely be observed in the lunar exosphere at high altitudes 10's of km. We demonstrate the usefulness and relevance of our model by examining mode: irregular grains, aggregate of spherical monomers and spherical grains with nano-phase iron inclusions. We subsequently simulate the scattering by two grain size distributions (0.1 and radius), and show the results normalized per-grain. A similar methodology can also be applied to the analysis of the LHG observations, which are believed to be produced by scattering from larger dust grains within about a meter of the surface.As expected, significant differences in scattering properties are shown between the analyses employing the widely used Mie theory and our more realistic grain geometries. These differences include large variations in intensity as well as a positive polarization of scattered sunlight caused by non-spherical grains. Positive polarization occurs even when the grain size is small compared to the wavelength of incident sunlight, thus confirming that the interpretation of LHG based on Mie theory could lead to large errors in estimating the distribution and abundances of exospheric dust.     

Processing Method Effects on Solar Diameter Measurements: Use of Data Gathered by the Solar Disk Sextant

To determine the apparent diameter of the Sun, it is first necessary to measure the shape of the intensity profile of the solar limb with an imaging optical system (hereafter denoted as a solar-limb profile). The inflection point of the limb profile is usually used as a reference for calculating the diameter. Because this point may be difficult to determine in the presence of noise, it is necessary to define an appropriate filtering process that eliminates noise while preserving the position of the inflection point. In this paper we study two filtering techniques, one based on the compact wavelet transform and the other on the finite Fourier transform definition, that meet these requirements. The application of these two techniques to data gathered by the Solar Disk Sextant experiment shows that the solar radius increased from 1992 to 1996 by about 197 mas. However, a previous analysis of the same data and our present analysis provide a difference in the measured radii of about 92 mas. We show that this difference is entirely traced to the filtering process.     

The Influence of Solar Flares on the Lower Solar Atmosphere: Evidence from the Na D Absorption Line Measured by GOLF/SOHO

Solar flares presumably have an impact on the deepest layers of the solar atmosphere and yet the observational evidence for such an impact is scarce. Using ten years of measurements of the Na D₁ and Na D₂ Fraunhofer lines, measured by GOLF onboard SOHO, we show that this photospheric line is indeed affected by flares. The effect of individual flares is hidden by solar oscillations, but a statistical analysis based on conditional averaging reveals a clear signature. Although GOLF can only probe one single wavelength at a time, we show that both wings of the Na line can nevertheless be compared. The varying line asymmetry can be interpreted as an upward plasma motion from the lower solar atmosphere during the peak of the flare, followed by a downward motion.     

Effects of an ambient medium on the emission,absorption and scattering of waves by atoms and molecules

A theory describing the interaction between atoms or molecules (or other systems with discrete energy eigenvalues) and waves in an arbitrary mode in an arbitrary ambient medium is developed. Rules for generalizing formulae describing processes for waves in vacuo to include the effects of a medium are stated and the illustrative examples of multipole radiation, the photo-electric effect and Rayleigh and Raman scattering are given.The following specific results are discussed: (1) In an isotropic medium with refractive indexn(), the rate of transitions with frequency isn(),n ³(), ... times that in vacuo for electric dipole, magnetic dipole or electric quadrupole, ..., transitions. (2) The conventional multipole expansion is inadequate when waves with a longitudinal component of polarization exist, but this does not affect the theory of electric and magnetic dipole transitions.A possible astrophysical application of resonant scattering by molecules of electron plasma waves is discussed briefly.     

The sunlit lunar atmosphere: A comprehensive study by CHACE on the Moon Impact Probe of Chandrayaan-1

The altitudinal/latitudinal profile of the lunar atmospheric composition on the sunlit side was unraveled for the first time by the Chandra’s Altitudinal Composition Explorer (CHACE) on the Moon Impact Probe, a standalone micro-satellite that impacted at the lunar south pole, as a part of the first Indian mission to Moon, Chandrayaan-1. Systematic measurements were carried out during the descent phase of the impactor with an altitude resolution of ∼250 m and a latitudinal resolution of ∼0.1°. The overall pressure on the dayside and the neutral composition in the mass range 1-100 amu have been measured by identifying 44 and 18 amu as the dominant constituents. Significant amounts of heavier (>50 amu) species also have been detected, the details of which are presented and discussed.     

Initial In-flight Results: The Total Solar Irradiance Monitor on the FY-3C Satellite,an Instrument with a Pointing System

The total solar irradiance (TSI) has been recorded daily since October 2013 by the Total Solar Irradiance Monitor (TSIM) onboard the FY-3C satellite, which is mainly designed for Earth observation. The TSIM has a pointing system to perform solar tracking using a sun sensor. The TSI is measured by two electrical substitution radiometers with traceability to the World Radiation Reference. The TSI value measured with the TSIM on 2 October 2013 is \(1364.88~\mbox{W}\,\mbox{m}^{-2}\) with an uncertainty of \(1.08~\mbox{W}\,\mbox{m}^{-2}\). Short-term TSI variations recorded with the TSIM show good agreement with SOHO/VIRGO and SORCE/TIM. The data quality and accuracy of FY-3C/TSIM are much better than its predecessors on the FY-3A and FY-3B satellites, which operated in a scanning mode.     

Spherical Oscillatory alpha2 Dynamo Induced by Magnetic Coupling between a Fluid Shell and an Inner Electrically Conducting Core: Relevance to the Solar Dynamo

A two-layer spherical alpha2 dynamo model consisting of an inner electrically conducting core (magnetic diffusivity lambdai and radius ri) with alpha=0 surrounded by an electrically conducting spherical shell (magnetic diffusivity lambdao and radius ro) with a constant alpha is shown to exhibit oscillatory behavior for values of beta=lambdai&solm0;lambdao and ri&solm0;ro relevant to the solar dynamo. Time-dependent dynamo solutions require ri&solm0;ro>/=0.55 and beta相似文献