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231.
232.
Nishant Mittal Joginder Sharma Vivek Tomar Udit Narain 《Planetary and Space Science》2009,57(1):53-57
We have analyzed the data for more than 12900 coronal mass ejections (CMEs) which were obtained by SOHO/LASCO during the period of 1996-2007. The online CME catalogue contains all major CMEs detected by LASCO C2 and C3 coronagraphs. Basically we determine the CME speeds from the linear and quadratic fits to the height-time measurements. It is found that linear (constant speed) fit is preferable for 90% of the CMEs. The distribution of speeds of CMEs in solar cycle 23 is presented along with those obtained by others. As expected, the speeds decrease in the decay phase of the cycle 23. There is an unusual drop in speed in the year 2001 and an abnormal increase in speed in the year 2003 due to the high concentration of CMEs, X-class soft X-ray flares, solar energetic particle (SEP) events and interplanetary shocks observed during October-November period called Halloween events. 相似文献
233.
For the mechanism of production of γ-ray bursts (GRBs) it is rather generally recognized that the long-term γ-ray burst (LGRB) originates from the deaths of massive stars while the short-term γ-ray burst (SGRB) originates from the merging of close binaries. Therefore the speculation naturally follows that the number of LGRBs is directly proportional to the star formation rate (SFR). However, it is indicated from recent data analyses that this speculation does not fit the observations very well. It is considered that only massive stars with masses greater than a certain critical mass can produce the LGRB, so the initial mass function (IMF) of stars can significantly affect the production rate of LGRBs. In this paper it is considered that the IMF of stars can be used to explain the observed number distribution of the LGRBs with the redshift, and this has led to some good results. 相似文献
234.
E. K. J. Kilpua P. C. Liewer C. Farrugia J. G. Luhmann C. Möstl Y. Li Y. Liu B. J. Lynch C. T. Russell A. Vourlidas M. H. Acuna A. B. Galvin D. Larson J. A. Sauvaud 《Solar physics》2009,254(2):325-344
We analyze a series of complex interplanetary events and their solar origins that occurred between 19 and 23 May 2007 using
observations by the STEREO and Wind satellites. The analyses demonstrate the new opportunities offered by the STEREO multispacecraft configuration for diagnosing
the structure of in situ events and relating them to their solar sources. The investigated period was characterized by two high-speed solar wind streams
and magnetic clouds observed in the vicinity of the sector boundary. The observing satellites were separated by a longitudinal
distance comparable to the typical radial extent of magnetic clouds at 1 AU (fraction of an AU), and, indeed, clear differences
were evident in the records from these spacecraft. Two partial-halo coronal mass ejections (CMEs) were launched from the same
active region less than a day apart, the first on 19 May and the second on 20 May 2007. The clear signatures of the magnetic
cloud associated with the first CME were observed by STEREO B and Wind while only STEREO A recorded clear signatures of the magnetic cloud associated with the latter CME. Both magnetic clouds
appeared to have interacted strongly with the ambient solar wind and the data showed evidence that they were a part of the
coronal streamer belt. Wind and STEREO B also recorded a shocklike disturbance propagating inside a magnetic cloud that compressed the field and plasma
at the cloud’s trailing portion. The results illustrate how distant multisatellite observations can reveal the complex structure
of the extension of the coronal streamer into interplanetary space even during the solar activity minimum.
Electronic Supplementary Material The online version of this article () contains supplementary material, which is available to authorized users. 相似文献
235.
We developed kinetic theory for the charging processes of small dust grains near the lunar surface due to interaction with the anisotropic solar wind plasma. Once charged, these dust grains, which are exposed to the electric field in the sheath region near the lunar surface, could loft and distribute around such heights off the surface where they reach equilibrium with the local gravitational force. Analytical solutions were derived for the charging time, grain floating potential, and grain charge, characterizing the charging processes of small dust grains in a two-component and in a multi-component solar wind plasma, and further highlighting the unique features presented by the high streaming plasma velocity. We have also formulated a novel kinetic theory of sheath formation around an absorbing planar surface immersed in the anisotropic solar wind plasma in the case of a negligible photoelectric effect and presented solutions for the sheath structure. In this study we combined the results from these analyses and provided estimates for the size distribution function of dust that is expected to be lofted in regions dominated by the solar wind plasma, such as near the terminator and in nearby shadowed craters. Corresponding to the two dominant streaming velocity peaks of 300 and 800 km/s, mean dust diameters of 500 and 350 nm, respectively, are expected to be found at equilibrium at heights of relevance to exploration operations, e.g., around 1.5 m height off the lunar surface. In shadowed craters near the terminator region, where isotropic plasma should be dominating, we estimate mean lofted dust diameter of 800 nm around the same 1.5 m height off the lunar surface. The generally applicable solutions could be used to readily calculate the expected lofted size distribution near the lunar surface as a function of plasma parameters, dust grain composition, and other parameters of interest. 相似文献
236.
Wang Kai-Rang Lin Jun Liu Lian-Guang Liu Chun-Ming Gao Guan-Nan 《Chinese Astronomy and Astrophysics》2012
Solar activities can cause the anomalies of electric power transmission systems, especially, for an extra-long distance transmission system. Using the data of coronal mass ejection (CME) from SOHO/LASCO (Solar and Heliospheric Observatory/Large Angle and Spectrometric Coronagraph), and the data of the geomagnetically induced current (GIC) and geomagnetic storm from the North China Electric Power University and Finnish Meteorological Institute, respectively, we analyze some important observational features and physical properties of the earth-directed halo CMEs associated with the GIC events. After classifying the observed halo CMEs according to their symmetry, it is found that the halo CMEs associated with GIC events are mainly the 3 types: completely symmetric, brightness-asymmetric, and outline-asymmetric. The geomagnetically induced current events driven by the three different types of halo CMEs have different characteristics in the intensity, duration, and period. We ?nd that the brightness-asymmetric halo CMEs are most likely to cause the major damage to the transmission systems. And that the geomagnetically induced current has also a good correlation with the time variation of geomagnetic ?eld. 相似文献
237.
238.
银河系的形成与演化是天体物理学研究的重大前沿课题,银河系的化学演化在其中更具有极其重要的地位。随着观测资料的不断积累和理论工作的不断深入,银河系化学演化的研究取得了一系列进展。在观测方面,从太阳附近区域,整个银盘,银晕和核球等方面简要回顾了银河系化学演化模型主要观测约束的近期结果;在化学演化模型方面,回顾了银河系化学演化研究的发展历程和近期进展,并对未来的研究进行了展望。 相似文献
239.
Adiabatic indices for a non-dissipative anisotropic convecting plasma are analyzed, and general expressions for the effective adiabatic index and the partial adiabatic indices parallel (γ∥) and perpendicular (γ⟂) to the magnetic field are obtained. It is shown that, in the general case, the value of the effective adiabatic index is not an universal constant and depends on the plasma temperature anisotropy and on the properties of the plasma motion. The values of γ⟂ and γ∥ are shown to be independent of the plasma parameters being completely determined by the characteristics of the plasma flow. 相似文献
240.
根据琼东南盆地深水区高分辨率2D/3D地震资料精细解释,和基于三维地震资料的相干分析,在琼东南盆地中央峡谷区发现了多期次的块体搬运沉积体系(MTDs)。研究表明,该区域块体搬运沉积体系包括3个主要的结构单元,即头部拉张区、体部滑移区和趾部挤压区,不同位置地震特征不同。大规模的块体搬运沉积体系构成了琼东南盆地中央峡谷区新近系以来地层中的重要沉积单元,并对深海沉积物的空间展布有重要的控制作用。上新世发育的一期块体搬运沉积体系,分布面积达300 km2,厚度达240 m,平面展布形态似扇形。高沉积物供给速率和不断的构造活动可能是该区域MTDs发育的主要原因。此外,地震活动、海平面变化也间接影响了MTDs的发育。 相似文献