On stereoimages of some structures in the solar atmosphere

Three-dimensional structures in the solar chromosphere and corona are considered. It is demonstrated that two photoheliograms separated by ～1 day can be used (using computer-graphics methods) to construct a stereo image of the Sun. The algorithm for this is presented and carried out for H_α images of the total disk. A bulge in the equatorial region resulting from the differential rotation of the Sun can be seen in the stereo image. Structures called Whitney pleats in catastrophe theory are observed in the solar corona. Such structures are encountered in prominences. The well-known helmets (or streamers) are pleats of heliospheric plasma sheets. Isophotes for such a sheet and the degree of polarization of the radiation in the pleat are calculated and compared with observational data.     

Gamma-ray radiation with energy 2.223 MeV and the density distribution in the solar atmosphere during flares

Interactions of particles accelerated in solar flares with matter in the solar atmosphere give rise to neutrons, which are efficiently captured on hydrogen nuclei as they are slowed to thermal velocities. This capture is accompanied by the emission of a gamma-ray with energy 2.223 MeV. Observational data for the temporal profiles of the gamma-ray fluxes in this line are used to study the plasma-density distribution in the solar atmosphere during the flares of December 16, 1988, March 22, 1991, and November 6, 1997. This analysis is based on comparisons between the observations and profiles computed taking into account a number of parameters describing the generation and transport of the flare neutrons in atmospheric layers of various densities. In three cases studied, the density of the material in the photosphere below the flare region is enhanced compared to the density in an unperturbed part of the solar atmosphere at the same height. In the case of the December 16, 1988 flare, we are able for the first time to relate the profile of the 2.223 MeV line with the shape of the accelerated particle (proton) spectrum. This opens new possibilities for studies of particle acceleration on the Sun based on observations of flare gamma-ray emission.     

The role of faculae in wave-energy transfer to upper layers of the solar atmosphere: Observations

The properties of Doppler-velocity oscillations in solar faculae are analyzed at the photospheric level (based on Fe I 6569 ? and Fe I 8536 ? lines) and chromospheric level (based on Hα and Ca II 8542 ? lines) to search for upward propagating waves. The similarity of the averaged power spectra at 2.5–4 mHz is not found to be convincing proof of the presence of unidirectional wave-energy transfer from the photosphere to the chromosphere. Phase relations between the photospheric and chromospheric oscillations that are indicative of either upward or downward propagating waves are obtained for various areas in many faculae. This suggests that the wave energy of the five-minute oscillations returns to the photosphere, at least partially. The derived properties suggest that the role of faculae in the transfer of the five-minute oscillations to the chromosphere and overlying layers is not as obvious as could be expected. The relatively typical presence of low-frequency (0.5–2 mHz) oscillations in faculae and their possible important role in this energy transfer are noted.     

The effect of acoustic waves on spectral-line profiles in the solar atmosphere: Observations and theory

The fine structure of the FeI λ 532.4185-nm line of neutral iron is studied with high spatial (0.5″) and temporal (9.3 s) resolution using observations of a quiet region at the center of the solar disk. The character of the line asymmetry depends strongly on the nature of the velocity field, i.e., on whether it is due to convective or wave motions. The magnitude of the asymmetry due to acoustic waves is comparable to that due to convective motions. The propagation of acoustic waves in moving granules and intergranular lanes is studied by solving a system of hydrodynamical equations in a three-dimensional model for the solar atmosphere. The temporal variations in the bisector of the line synthesized in a non-LTE approximation agree well with the observational data.     

f-x域共偏移距道集的EEMD随机噪声压制方法

f-x域随机噪声压制方法面临着2个问题:叠前共炮点道集或CMP道集反射波同相轴为双曲线型,去噪同时会损害有效波;地震信号为复杂的非平稳信号,要求去噪方法具有自适应性。基于f-x EEMD的共偏移距道集随机噪声压制方法利用了共偏移距道集反射波同相轴为水平满足f-x域去噪假设条件和EEMD算法对非平稳信号的良好适应性,对f-x域每一个等频率切片做EEMD分解,并去除以高频随机噪声为主的第一个IMF分量,最后将f-x域数据反变换回t-x域,实现噪声分离。正演模拟和实际地震数据试算结果表明:该方法在压制随机噪声的同时,能够保持有效信号。      

Weekly cycle in the atmosphere

Doklady Earth Sciences -     

倾斜CCP道集抽取方法及影响因素分析

界面上三维PS波(反射转换横波)的转换点在地表有相应的界面法向投影点,抽取CCP (共转换点)道集的实质就是确定不同方位上投影点距离炮点和对应检波点的比例关系。当界面倾斜时,该比例关系是界面的倾角、倾向、法向深度、炮检方位以及纵横波速度比等参数的函数。就上述参数通过这一比例关系是如何影响共转换点道集的构成及影响程度设计了特定的模型进行讨论。计算结果表明,忽视倾斜界面的影响将引起转换波抽道集的混乱,并造成后期成像的错误。     

基于优化处理的宽角度道集密度反演及应用

用密度属性参数进行含油气预测在海洋地震勘探中应用比较广泛,准确反演密度是油气检测的关键,文中探讨叠前道集优化处理对密度反演精度的影响,从叠前道集质量评价及优化处理出发,改善地震资料的品质(信噪比、振幅补偿合理性、远近道频率差异性),保证宽角度有效地震信号,提高道集资料保真度。在此基础上利用叠前三参数反演方法,获得密度参数,以此进行含油气预测。通过盲井验证,处理后道集资料有效提高了密度反演的精度,这将为油气勘探提供新的手段。     

基于目标性滤波器的倾角道集绕射体成像

利用绕射能量对地下异常地质体进行精确成像是近年地震勘探的突破性技术进展之一。通过对倾角道集滤波后叠加成像,是有效利用地震绕射信息的主要技术手段。本文应用灵活和高效的计算方法生成倾角成像道集,同时设计高效倾角目标性滤波器,应用于倾角成像道集,通过模型试算分析反射能量和绕射能量在倾角道集中的区别与联系,实现更高效的绕射能量与反射能量的滤波分离。中国西北地区缝洞型油气储集体对绕射波比较敏感,通过对该区的实际数据应用测试,实现了更加节省计算时间同时具有更高成像精度绕射波成像的效果。     

基于G-D波场分解的角度域共成像点道集提取及成像

通常的叠前深度偏移都是通过偏移距域共成像道集和炮域共成像道集来实现的,这里则通过对G-D波场局部平面波的分解,提出了局部角度域共成像点道集方法,从而改善了偏移成像速度及效果,为研究地下构造,岩性分析以及偏移速度分析提供新的途径。     

Photochemistry of methane in the Earth's early atmosphere

A detailed model is presented of methane photochemistry in the primitive terrestrial atmosphere along with speculation about its interpretation. Steady-state CH₄ mixing ratios of 10⁻⁶–10⁻⁴ could have been maintained by a methane source of about 10¹¹ cm⁻² s⁻¹, which is comparable to the modern biogenic methane production rate. In the absence of a source, methane would have disappeared in <10⁴ years, being either oxidized, or polymerized into more complex hydrocarbons. The source strength needed to maintain a steady CH₄ mixing ratio and the degree to which methane could have polymerized to form higher hydrocarbons depend upon the amount of CO₂ present in the early atmosphere. The dependence on H₂ is much weaker. Infrared absorption by methane, and especially by other hydrocarbon species, may have supplemented the greenhouse warming due to carbon dioxide. A radiative model is needed to establish this effect quantitatively. The destruction of the methane greenhouse early in the Proterozoic may have triggered the Huronian glaciation.These calculations also suggest that atmospheres rich in both CO₂ and CH₄ may be photochemically unstable with respect to conversion to CO.     

Oxygen and ozone in the early Earth's atmosphere

The precise amount of O₂ and O₃ in the Earth's prebiological paleoatmosphere has been a topic of considerable discussion in the past. Since the photolysis of H₂O and CO₂, the prebiological mechanisms to produce O₂, depends on the ultraviolet (UV) flux from the Sun, a reliable quantification of the problem requires detailed knowledge of such flux. Using the most recent astronomical observation of young stars from the International Ultraviolet Explorer, as well as a detailed photochemical model of the paleoatmosphere, we find that the amount of O₂ in the prebiological paleoatmosphere may have been as much as 10⁶ times greater than previously estimated.Some of the implications of this new value are discussed.     

Total precipitable water in the atmosphere over India

Electromagnetic radiation, in its passage through the atmosphere, is attenuated by absorption and scattering by atmospheric gases, dust and aerosols. The most important absorber is water vapour and the most significant parameter in atmospheric absorption studies is the total precipitable water in the atmosphere. The present paper summarises the results of a study made to compute the total precipitable water in the atmosphere over India using radiosonde and other data, as part of a programme for the computation of direct, global and diffuse solar radiation at the ground from the solar constant. Using values of air temperature and dew point from the ground up to 250 mb at 19 radiosonde stations and surface water vapour mixing ratio values at 105 surface observatories in India, precipitable water amounts have been computed for 124 stations, for each month and for the whole year. The paper describes the techniques used to extend the total precipitable water amounts derived from radiosonde data at 19 stations to 124 stations covering the major climatic zones in the country and presents the results in the form of 12 maps showing the spatial and temporal distribution of total precipitable water over India     

Helicity in the upper atmosphere and Ekman-type instabilities

Based on a certain analogy between the physical conditions in the region of the upper atmosphere, transitional from the mesosphere to the lower thermosphere (MLT), and the atmospheric boundary layer (ABL), for the first time for the upper atmosphere we obtained helicity estimates and analyzed the Ekmantype instability. The performed calculations of the orientation of the formed periodic structures agree with the experimental data.     

Solar forcing of the terrestrial atmosphere

The Sun provides the main energy input to the terrestrial atmosphere, and yet the impact of solar variability on long-term changes remains a controversial issue. Direct radiative forcing is the most studied mechanism. Other much weaker mechanisms, however, can have a significant leverage, but the underlying physics is often poorly known. We review the main mechanisms by which solar variability may impact the terrestrial atmosphere on time scales ranging from days to millennia. This includes radiative forcing, but also the effect of interplanetary perturbations and energetic particle fluxes, all of which are eventually driven by the solar magnetic field.     

Carbon dioxide and nitrogenous gases in the soil atmosphere

Carbon dioxide and nitrogenous trace gases (N₂O, NO) in the soil atmosphere are mainly the products of microbially mediated processes. Once produced, these gases pass to the overlying atmosphere primarily via molecular diffusion, a process which is described by Fick's law of diffusion.In a diffusion-dominated soil, the partial pressure, or concentration, of CO₂ in the soil atmosphere varies as a function of soil depth and is dependent on the production rate and diffusivities. Since these parameters are highly variable, CO₂ concentrations vary widely both between, and within, differing ecosystems. In a compilation of data from around the world, arranged according to an ecosystem classification, soil CO₂ concentrations varied from 0.04 to 13.0% by volume in the upper several meters of soil. These data also highlight the importance of organic substrate (soil organic matter, roots, root exudates), temperature, and (to some extent) moisture on CO₂ production and the resulting concentration in soil profiles. The δ¹³C of the soil CO₂ also varies as a function of depth due to differences in the δ¹³C of the organic substrate undergoing decomposition and the mixing with CO₂ of the overlying atmosphere. Recent work suggests that the δ¹⁸O of the soil CO₂ may hold some promise in estimating the δ¹⁸O of soil water.Biological production and consumption of N₂O and NO results primarily from activity of nitrifying and denitrifying bacteria. Ammonium limitation of nitrification and organic carbon limitation of denitrification usually restricts these processes to surface soil horizons, although denitrification may be an important process for reducing NO₃⁻ in groundwater. These microbial processes and the relative proportions of their gaseous end products are strongly influenced by redox conditions. Microsite variation in sources of electron donors and acceptors is critical to understanding rates and distributions of N trace gas production. Several abiological oxidation and reduction reactions are also important, and interaction of biological and abiological processes deserves more research attention.