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191.
In the present phase of the solar cycle no big transients leading to strong modulation had been observed after 1991. Apart from a few minor disturbances cosmic rays were still recovering to a new intensity maximum. It was suggested, therefore, that existing literature from previous cycles should be critically reviewed. The scene was set by the introductory papers on— phenomenology of cosmic ray modulation in successive solar cycles throughout the heliosphere— the present state of models for long term modulation and their shortcomings— the relation between cosmic ray variations and the magnitude of the interplanetary magnetic field (the CR-B-relation)— charge dependent effects.In the discussions, the study of propagating diffusive disturbances and the CR-B-relation played a central role. The difference was stressed between isolated transient disturbances in the inner solar system (Forbush decreases), and the long lasting, step-like decreases caused by merged interaction regions in the outer heliosphere. The recovery rates following the step-like decreases vary with the phase in the 22-year solar cycle. In some cases this requires a modification of existing drift models. In the outer heliosphere, the CR-B-relation leads to the result 1/ between the diffusion coefficient and the field magnitude . This simple result is a challenge for theoreticians to derive the perpendicular diffusion coefficient fromfirst principles. The three articles in this report essentially follow the list of open points and arguments just presented.The article "Observations and Simple Models" is organised around the model of a propagating diffusive barrier, its application to Forbush effects in the inner heliosphere and to decreases caused by merged interaction regions in the outer heliosphere. Acomparison of observed Forbush decreases with model predictions requires a careful separation of the two steps related to the turbulent region behind the shock front and the closed magnetic field regions of the ejecta (the interplanetary counterparts of coronal mass ejections). It is shown that models for propagating disturbances can be used to derive values of the diffusion coefficients phenomenologically, not only during the disturbance, but also in the ambient medium.The "Modeling of Merged Interaction Regions" summarizes the dynamic and time-dependent process of cosmic ray modulation in the heliosphere. Numerical models with only a time-dependent neutral sheet prove to be successful when moderate to low solar activity occurs but fail to describe large and discrete steps in modulated cosmic rays when solar activity is high. To explain this feature of heliospheric modulation, the concept of global merged interaction regions is required. The com-bination of gradient, curvature and neutral sheet drifts with these global merged interaction regions has so far been the most successful approach in explaining the 11-year and 22-year cycles in the long-term modulation of cosmic rays.The "Remarks on the Diffusion Tensor in the Heliosphere" describe available theories of perpen-dicular diffusion and drift, and discuss their relevance to cosmic rays in the heliosphere. In addition, the information about diffusion coefficients and spatial gradients obtained from the analysis of steady state anisotropies at neutron monitor energies is summarized. These topics are intimately related to the other two articles. They are also part of the general discussion about the "Diffusion Tensor throughout the Heliosphere" which played an important role in all working groups. 相似文献
192.
Klecker B. Mewaldt R.A. Bieber J.W. Cummings A.C. Drury L. Giacalone J. Jokipii J.R. Jones F.C. Krainev M.B. Lee M.A. Le Roux J.A. Marsden R.G. Mcdonald F.B. McKibben R.B. Steenberg C.D. Baring M.G. Ellison D.C. Lanzerotti L.J. Leske R.A. Mazur J.E. Moraal H. Oetliker M. Ptuskin V.S. Selesnick R.S. Trattner K.J. 《Space Science Reviews》1998,83(1-2):259-308
We review the observed properties of anomalous cosmic rays and the present status of our knowledge of the processes by which they originate. We compiled a comprehensive set of ACR energy spectral data from various spacecraft throughout the heliosphere during the passes of Ulysses over the poles of the Sun and present first results of a detailed modeling effort. In several contributions, we discuss the questions of injection and possible pre-acceleration of pickup ions, summarize new observations on the ionic charge composition, and present new results on the composition of minor ions in ACRs. 相似文献
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N. Cornilleau-Wehrlin P. Chauveau S. Louis A. Meyer J. M. Nappa S. Perraut L. Rezeau P. Robert A. Roux C. De Villedary Y. De Conchy L. Friel C. C. Harvey D. Hubert C. Lacombe R. Manning F. Wouters F. Lefeuvre M. Parrot J. L. Pinçon B. Poirier W. Kofman Ph. Louarn 《Space Science Reviews》1997,79(1-2):107-136
The Spatio-Temporal Analysis of Field Fluctuations (STAFF) experiment is one of five experiments which together comprise the Wave Experiment Consortium (WEC). STAFF consists of a three-axis search coil magnetometer to measure magnetic fluctuations at frequencies up to 4 kHz, and a spectrum analyser to calculate in near-real time aboard the spacecraft, the complete auto- and cross-spectral matrices using the three magnetic and two electric components of the electromagnetic field. The magnetic waveform at frequencies below either 10 Hz or 180 Hz is also transmitted. The sensitivity of the search coil is adapted to the phenomena theo be studied: the values 3 × 10-3 nT Hz-1/2 and 3 × 10-5 nT Hz-1/2 are achieved respectively at 1 Hz and 100 Hz. The dynamic range of the STAFF instruments is about 96 dB in both waveform and spectral power, so as to allow the study of waves near plasma boundaries. Scientific objectives of the STAFF investigations, particularly those requiring four point measurements, are discussed. Methods by which the wave data will be characterised are described with emphasis on those specific to four-point measurements, including the use of the Field Energy Distribution function. 相似文献
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The Polar Ionospheric X-ray Imaging Experiment (PIXIE) 总被引:2,自引:0,他引:2
W. L. Imhof K. A. Spear J. W. Hamilton B. R. Higgins M. J. Murphy J. G. Pronko R. R. Vondrak D. L. McKenzie C. J. Rice D. J. Gorney D. A. Roux R. L. Williams J. A. Stein J. Bjordal J. Stadsnes K. Njoten T. J. Rosenberg L. Lutz D. Detrick 《Space Science Reviews》1995,71(1-4):385-408
The Polar Ionospheric X-ray Imaging Experiment (PIXIE) is an X-ray multiple-pinhole camera designed to image simultaneously an entire auroral region from high altitudes. It will be mounted on the despun platform of the POLAR spacecraft and will measure the spatial distribution and temporal variation of auroral X-ray emissions in the 2 to 60 keV energy range on the day side of the Earth as well as the night. PIXIE consists of two pinhole cameras integrated into one assembly, each equipped with an adjustable aperture plate that allows an optimum number of nonoverlapping images to be formed in the detector plane at each phase of the satellite's eccentric orbit. The aperture plates also allow the pinhole size to be adjusted so that the experimenter can trade off spatial resolution against instrument sensitivity. In the principal mode of operation, one aperture plate will be positioned for high spatial resolution and the other for high sensitivity. The detectors consist of four stacked multiwire position-sensitive proportional counters, two in each of two separate gas chambers. The front chamber operates in the 2–12 keV energy range and the rear chamber in the 10–60 keV range. All of the energy and position information for each telemetered X-ray event is available on the ground. This enables the experimenter to adjust the exposure timepostfacto so that energy spectra of each X-ray emitting region can be independently accumulated. From these data PIXIE will provide, for the first time, global images of precipitated energetic electron spectra, energy inputs, ionospheric electron densities, and upper atmospheric conductivities. 相似文献
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为改进隐身飞行器推进系统的气动性能,针对S弯进气道开展了设计和分析。基于数值模拟方法、代理模型和遗传算法构建了一套自动优化方法。在优化设计过程中,结合参数化建模、网格自动生成和改进(SST)湍流模型求解,应用优化方法对飞行器进行了多目标设计,得到了进气道的优化推荐构型。应用尺度自适应模拟(SAS)方法对优化进气道气动性能进行了全面和细致的分析。研究结果表明:SAS方法可以较好地模拟S弯进气道的流动,优化设计能够极大地改进S弯进气道的气动性能;相比原始设计,优化进气道设计点的总压畸变指数降低了16.3%,总压恢复系数提高了1.1%。 相似文献
200.
斯德谊 《北京航空航天大学学报》1998,(5):2
提出了用均匀平行线阵和阵元输出信号的时间延迟估计时间欠采样来波频率、方位角和仰角的方法.该算法在DFT波束空间使用PROESPRIT方法,实现频率无模糊估计,完成来波信号频率和角度的估计.频率间接估计算法是先估计数字频率,然后用数字频率求模拟频率,其估计方差比直接估计算法的方差要小几个数量级.仿真实验表明了算法的有效性. 相似文献