Intensity Fluctuations of Radiation Escaping from a Multicomponent Stochastic Atmosphere. I

This is the first part of a paper devoted to a theoretical investigation of intensity fluctuations of radiation at the frequencies of a spectral line formed in a multicomponent stochastic atmosphere. It is assumed that the optical depth of structural elements and the power of the energy sources contained in them undergo random variations. The frequency dependence of the relative mean-square deviation of the intensity of radiation escaping from the atmosphere is determined. Two special cases are considered and it is shown that the behavior of this quantity is different, depending on which of the indicated characteristics of the medium undergoes random variations. The results make it possible to judge the character of random variations in the fine structure of a radiating medium from observations of it in the cores and wings of spectral lines. Recent observations of prominences made using the SUMER spectrometer in the SOHO international project served as the specific motivation for the work.     

Vertical Chromium Distribution in the Atmosphere of a Chemically Peculiar Star. I. Diagnostics

On the basis of CCD spectrograms obtained with high resolution at the Coudé focus of the 2.6-m telescope of the Crimean Astrophysical Observatory, Cr II lines lying in the wings of the H hydrogen line are investigated. Vertical chromium stratification in the atmospheres of two normal and eight chemically peculiar stars is diagnosed using the method of spectral synthesis. An increase in Cr abundance with depth is found for the cool Ap stars CrB, HR 7575, Equ, and 10 Aql. Some increase in Cr abundance in the upper layers of the atmosphere is presumed for all Am stars and for both Hg—Mn components of 46 Dra. The vertical chromium distribution in the atmospheres of the hot, spotted Ap stars 17 Com and ² CVn is evidently uniform.     

Scattering in the Atmosphere of Venus. I. Line profiles and curves of growth for isotropic scattering

We have computed line profiles and curves of growth for both reflected and transmitted radiation for typical lines in CO₂ bands (in the photographic infrared) which occur in the spectrum of Venus. In our model the pressure variation with altitude was considered and the base of the cloud deck was set at the 2 bar level. The temperature was held constant at 250K and a Voigt profile was used for the lineshape. We also assumed that the scale height of the cloud particles was equal to the scale height of the gas. The calculations were made for four values of the scattering optical thickness (τ_c = 0.1, 1.0, 10, and 100) using a continuum single scattering albedo $\text{ω}{}_{\mathrm{<mtext>c</mtext>}}\text{= 0.9975}$ (which gives a Bond albedo of 0.896 for τ_c = 100, the value observed for Venus at these wavelengths). Curves of growth are also presented for reflected radiation which has been averaged over the visible disk for three values of the Venus phase angle (0, 86, and 166°).     

Jupiter: Aerosol Chemistry in the Polar Atmosphere

Aromatic compounds have been considered a likely candidate for enhanced aerosol formation in the polar region of Jupiter. We develop a new chemical model for aromatic compounds in the Jovian auroral thermosphere/ionosphere. The model is based on a previous model for hydrocarbon chemistry in the Jovian atmosphere and is constrained by observations from Voyager, Galileo, and the Infrared Space Observatory. Precipitation of energetic electrons provides the major energy source for the production of benzene and other heavier aromatic hydrocarbons. The maximum mixing ratio of benzene in the polar model is 2x10-9, a value that can be compared with the observed value of 2+2-1x10-9 in the north polar auroral region. Sufficient quantities of the higher ring species are produced so that their saturated vapor pressures are exceeded. Condensation of these molecules is expected to lead to aerosol formation.     

DTM94大气模型及其应用

简述了ＤＴＭ９４ 大气模型, 并以其旧版本ＤＴＭ７８ 为对照进行了初步考察和分析, 其中给出了两种模型的大气密度随地磁指数ｋｐ 和太阳辐射流量（Ｓｏｌａｒ Ｒａｄｉｏ Ｆｌｕｘ） 变化的情况, 并对２０ｄ （ 天） 弧长Ａｊｉｓａｉ 卫星的全球ＳＬＲ观测资料进行处理, 结果表明ＤＴＮ９４ 对近地卫星Ａｊｉｓａｉ 的精密定轨是十分有利的。     

湍流大气的像质衰减参数及测量

讨论了经过大气后天文图象的象质衰减,研究了对这种衰减进行描述的视宁度参数ｒ０及其它几个大气光学参数,介绍了几种测量象质衰减参数的方法,重点介绍了我们将差分像运动法运用于白日视宁度测量的尝试以及新设计的可兼顾昼夜的视宁度测量仪,仪器已用于云台白日的视宁度测量。最后对近场近似假设进行了定量分析,在此基础上给出了新确定的近场近似成立的范围,这一范围比以前所给的要更大些。     

The Atmosphere of Io: Abundances and Sources of Sulfur Dioxide and Atomic Hydrogen

An analysis and interpretation of reflected solar Lyman α intensity data acquired with the Hubble Space Telescope (HST) implies an equatorially confined atmosphere with SO₂ column densities ∼ 1–2 × 10¹⁶ cm^-2. Poleward of 30° the SO₂ density must decrease sharply reaching an asymptotic polar value of < 10¹⁵ cm^-2 at 45° to achieve the observed 2 kR intensity peaks. The corresponding surface reflectivities must be either a constant 0.047 for higher equatorial SO₂ or a variable reflectivity of 0.027 with lower SO₂ densities at the equator increasing to a polar value of ∼ 0.05. The average residence time for an atmospheric SO₂ molecule is ∼ 2–3 days for the canonical mass loading rate of the Io plasma torus = 10³⁰ amu s^-1. With atomic hydrogen in the atmosphere and corona constrained by the HST observations, it is estimated that a pickup proton density ratio of 0.25–0.4% can be sustained by a supply of Io plasma torus protons neutralized in Io's atmosphere/exosphere, if protons constitute 7% of the total torus ion density, which is close to the Chust et al. (1999) pickup proton density ratio and under the widely quoted 10% proton content of the torus. This revised version was published online in July 2006 with corrections to the Cover Date.     

Oscillations in the Umbral Atmosphere

The results of simultaneous observations of oscillations in the chromosphere, transition region, and corona above nine sunspots are presented. The data are obtained through coordinated observing with the Solar and Heliospheric Observatory — SOHO and the Transition Region And Coronal Explorer — TRACE. Oscillations are detected above each umbra. The power spectra show one dominant frequency corresponding to a period close to 3 min. We show that the oscillations in the sunspot transition region can be modeled by upwardly propagating acoustic waves. In the corona the oscillations are limited to small regions that often coincide with the endpoints of sunspot coronal loops. Spectral observations show that oscillations in the corona contribute to the observed oscillations in the TRACE 171 Å channel observations. We show that a recent suggestion regarding a connection between sunspot plumes and 3-min oscillations conflicts with the observations.     

Seismology of a Sunspot Atmosphere

Two competing theories of sunspot oscillations are discussed. It is pointed out that the normal mode (eigenoscillations) theory is in contradiction with a number of observations. The reasons for this are discussed. The revised filter theory of the three-minute sunspot oscillations is outlined. It is shown that the reason for the occurrence of the multipassband filter for the slow waves is the interference that appears from the multilayer structure of the sunspot atmosphere. In contrast with Zhugzhda and Locans (Sov. Astron. Lett. 7, 25?–?27, 1981) it is shown that along with the Fabry?–?Perot chromospheric passband the cutoff frequency passband and a number of the high-frequency passbands occur. The effect of the nonlinearity of the sunspot oscillations in the upper chromosphere and the transition region is taken into account. The spectra of the distinct empirical models of the sunspot atmosphere are explored. An example of the interpretation of the sunspot oscillations based on the revised filter theory is presented. Only the filter theory can explain the complicated behavior of the oscillations across the sunspot. The observations provide evidence of the nonuniformity of the sunspot atmosphere.     

Photochemistry and Vertical Transport in Io's Atmosphere and Ionosphere

We present an updated model for the photochemistry of Io's atmosphere and ionosphere and use this model to investigate the sensitivity of the chemical structure to vertical transport rates. SO₂is assumed to be the dominant atmospheric gas, with minor molecular sodium species such as Na₂S or Na₂O released by sputtering or venting from the surface. Photochemical products include SO, O₂, S, O, Na, NaO, NaS, and Na₂. We consider both “thick” and “thin” SO₂atmospheres that encompass the range allowed by recent HST and millimeter-wave observations, and evaluate the possibility that O₂and/or SO may be significant minor dayside constituents and therefore likely dominant nightside gases. The fast reaction between S and O₂limits the column abundance of O₂to ∼10⁴less than that calculated by Kumar (J. Geophys. Res.87, 1677–1684, 1982; 89(A9), 7399–7406, 1984) for a pure sulfur/oxygen atmosphere. If a significant source of NaO₂or Na₂O were supplied by the surface and mixed rapidly upward, then oxygen liberated in the chemical reactions which also liberate free Na would provide an additional source of O₂. Fast eddy mixing will enhance the transport of molecular sodium species to the exobase, in addition to increasing the vertical transport rate of ions. Ions produced in the atmosphere will be accelerated by the reduced corotation electric field penetrating the atmosphere. These ions experience collisions with the neutral gas, leading to enhanced vertical ion diffusion. The dominant ion, Na⁺, is lost primarily by charge exchange with Na₂O and/or Na₂S in the lower atmosphere and by diffusion through the ionopause in the upper atmosphere. The atmospheric column abundance of SO, O₂, and the upper atmosphere escape rates of Na, S, O, and molecular sodium species are all strong functions of the eddy mixing rate. Most atmospheric escape, including that of molecular sodium species, probably occurs from the low density “background” SO₂atmosphere, while a localized high density “volcanic” SO₂atmosphere can yield an ionosphere consistent with that detected by the Pioneer 10 spacecraft.     

Comments on the Bilderberg Continuum Atmosphere

The Bilderberg Continuum Atmosphere fails to reproduce the observed limb-darkening throughout the range of wavelengths 4500 Å<< 25 000 Å. The temperature-pressure diagram for the deep layers of this model is a curve which is flatter than the relation predicted from the mixing length theory. A modification of the Bilderberg Continuum Atmosphere that improves representation of the observations and theoretical results is proposed.The work described here was supported in part by Contract N(onr)-1224(19) with the Office of Naval Research.     

太阳大气铍丰度的衰减

Li和Be轻元素在温度仅几百万度时就因核反应而遭毁坏,因此它们是恒星演化过程的外层对流混合延伸程度很好的一种示踪。基于这种考虑,我们曾计算过太阳包层模型Li的衰减,得到一个同时满足日震学太阳对流区深度和太阳Li丰度观测要求的非局部太阳对流包层模型[1].Li丰度给出了一个非局部对流混合延伸程度的上限。     

Small Comets in the High Atmosphere

Recent claims of small icy comets disintegrating in the high atmosphere point to a component of comets in the form of loose aggregates of dust. This could be understood in terms of Lyttleton;'s theory of comet formation by accretion of interstellar grains. This revised version was published online in July 2006 with corrections to the Cover Date.     

The Porous Atmosphere of eta Carinae

We analyze the wind generated by the great 20 yr-long super-Eddington outburst of eta Carinae. We show that by using the classical stellar atmosphere and wind theory, it is impossible to construct a consistent wind model in which a sufficiently small amount of mass, like the one observed, is shed. One expects the super-Eddington luminosity to drive a thick wind with a mass-loss rate substantially higher than the observed one. The easiest way to resolve the inconsistency is if we alleviate the implicit notion that atmospheres are homogeneous. An inhomogeneous, or "porous," atmosphere allows more radiation to escape while exerting a smaller average force. Consequently, such an atmosphere yields a considerably lower mass-loss rate for the same total luminosity. Moreover, all the applications of the Eddington luminosity as a strict luminosity limit should be revised or at least reanalyzed carefully.     

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.     

Stochastic Models of Hot Planetary and Satellite Coronas: Suprathermal Nitrogen in Titan's Upper Atmosphere

The processes of dissociation and dissociative ionization of molecular nitrogen by solar UV radiation and by the accompanying flux of photoelectrons, as well as sputtering of the atmosphere by fluxes of magnetospheric ions and pick-up ions, are the main sources of translationally excited (hot, or suprathermal) nitrogen atoms and molecules in Titan's upper atmosphere. Since Titan does not possess an intrinsic magnetic field, ions from Saturn's magnetosphere can penetrate into the outer layers of Titan's atmosphere and sputter atoms and molecules from the atmosphere in momentum-transfer and charge exchange collisions. Atmospheric sputtering by corotating nitrogen ions and carbon-containing pick-up ions, as well as photodissociation-related losses, was considered previously by Lammer and Bauer (1993) and Shematovich et al. (2001, 2003). In this paper we investigate the processes of the formation and evolution of the fraction of suprathermal nitrogen atoms and molecules in the transition region of Titan's upper atmosphere using the previously developed Monte Carlo model for hot satellite and planetary coronas (Shematovich, 1999, 2004). It is established that the suprathermal nitrogen fraction in the transition region of Titan's upper atmosphere includes nitrogen atoms and molecules but the suprathermal nitrogen concentration is relatively small owing to high rates of escape from the atmosphere and to the efficient thermalization of suprathermal nitrogen at the altitudes of the relatively dense lower thermosphere. However, the scale height for suprathermal nitrogen in the transition region is much higher than that for the ambient atmospheric gas. Therefore, suprathermal nitrogen becomes one of the dominant components in the outer exosphere.     

Spectroscopic Data of W I,Mo I and Cr I Spectral Lines: Selection and Analysis

Plasma of electric arc discharges between composite Cu–W, Cu–Mo and Cu–Cr electrodes in argon flow and their spectra were studied by optical emission spectroscopy. Since values of oscillator strengths for W I, Mo I and Cr I presented in various sources are significantly different, selection of spectroscopic data for these elements (particularly oscillator strength) was expected to be useful for plasma diagnostics. The Boltzmann plot method was used as a tool for the selection of appropriate spectral lines and their spectroscopic data. The main result of the paper is W I, Mo I and Cr I spectral lines and spectroscopic data recommended for diagnostics of plasma with such metal impurities.     

太阳大气中的光球亮点

首先是对太阳光球亮点近年来研究工作的总结。光球亮点是一种发生在太阳光球上宁静区域的的小尺度和短寿命增亮现象,平均直径在100～300knm之间,平均寿命约为几分钟。光球亮点的研究对于光球辐射和磁场性质的认识具有重要意义。过去的观测显示,绝大多数光球亮点的产生和演化与磁场,特别是光球上的小尺度磁场的演化密切相关,比如,两个同极性磁场的合并,或者反极性磁场的对消,或者一个同极性磁场的分裂,均可以促使光球亮点产生或消失。基于这样的观测结果,统计研究了2722个光球亮点(1600A)与光球上偶极磁元的关系,发现大约有1/3的光球亮点出现在偶极磁元中心附近。     

Turbulence In The Solar Atmosphere: Manifestations And Diagnostics Via Solar Image Processing

Intermittent magnetohydrodynamical turbulence is most likely at work in the magnetized solar atmosphere. As a result, an array of scaling and multi-scaling image-processing techniques can be used to measure the expected self-organization of solar magnetic fields. While these techniques advance our understanding of the physical system at work, it is unclear whether they can be used to predict solar eruptions, thus obtaining a practical significance for space weather. We address part of this problem by focusing on solar active regions and by investigating the usefulness of scaling and multi-scaling image-processing techniques in solar flare prediction. Since solar flares exhibit spatial and temporal intermittency, we suggest that they are the products of instabilities subject to a critical threshold in a turbulent magnetic configuration. The identification of this threshold in scaling and multi-scaling spectra would then contribute meaningfully to the prediction of solar flares. We find that the fractal dimension of solar magnetic fields and their multi-fractal spectrum of generalized correlation dimensions do not have significant predictive ability. The respective multi-fractal structure functions and their inertial-range scaling exponents, however, probably provide some statistical distinguishing features between flaring and non-flaring active regions. More importantly, the temporal evolution of the above scaling exponents in flaring active regions probably shows a distinct behavior starting a few hours prior to a flare and therefore this temporal behavior may be practically useful in flare prediction. The results of this study need to be validated by more comprehensive works over a large number of solar active regions. Sufficient statistics may also establish critical thresholds in the values of the multi-fractal structure functions and/or their scaling exponents above which a flare may be predicted with a high level of confidence. Based on the author's contributed talk “Manifestations and Diagnostics of Turbulence in the Solar Atmosphere”, presented at the Solar Image Processing Workshop II, Annapolis, Maryland, USA, 3–5 November 2004.