共查询到20条相似文献,搜索用时 31 毫秒
1.
E.J. Smith 《Journal of Atmospheric and Solar》2011,73(2-3):277-289
Important contributions of Ulysses to understanding the solar cycle evolution of the heliospheric magnetic field (HMF) and solar wind are reviewed: a dramatic reorientation of the HMF as the solar dipole rotates between axial and equatorial orientations; solar cycle variation of the total heliospheric magnetic flux and its response to changes in solar magnetic fields; the unusual on-going solar minimum and its effects; a connection between magnetic flux and solar wind mass flux in the heliosphere and at the source; a recurrent north–south heliospheric asymmetry at solar minimum and the equatorial offset of the solar magnetic dipole. 相似文献
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采用二维理想MHD模型,分别在日球赤道面(二维二分量模型)和日球子午面(二维 三分量模型)内研究太阳风中纯速度增幅扰动的演化. 结果表明,该扰动在向外传播的过程 中逐渐演化为双重激波对,即由4个激波组成的激波系统. 该4个激波按离太阳由近及远依次 为后向快激波、后向慢激波、前向慢激波和前向快激波. 双重激波对在子午面内相对扰动源 中心法线基本对称,而在赤道面内则不对称:扰动源中心法线西侧双重激波对结构更为明显 ,所跨经度范围宽于东侧. 初步分析表明,行星际磁场的螺旋结构是产生日球赤道面内双重 激波对结构东西不对称性的主要原因. 相似文献
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Gang Li 《中国科学:地球科学(英文版)》2017,60(8):1440-1465
In the solar system, our Sun is Nature’s most efficient particle accelerator. In large solar flares and fast coronal mass ejections (CMEs), protons and heavy ions can be accelerated to over ~GeV/nucleon. Large flares and fast CMEs often occur together. However there are clues that different acceleration mechanisms exist in these two processes. In solar flares, particles are accelerated at magnetic reconnection sites and stochastic acceleration likely dominates. In comparison, at CME-driven shocks, diffusive shock acceleration dominates. Besides solar flares and CMEs, which are transient events, acceleration of particles has also been observed in other places in the solar system, including the solar wind termination shock, planetary bow shocks, and shocks bounding the Corotation Interaction Regions (CIRs). Understanding how particles are accelerated in these places has been a central topic of space physics. However, because observations of energetic particles are often made at spacecraft near the Earth, propagation of energetic particles in the solar wind smears out many distinct features of the acceleration process. The propagation of a charged particle in the solar wind closely relates to the turbulent electric field and magnetic field of the solar wind through particle-wave interaction. A correct interpretation of the observations therefore requires a thorough understanding of the solar wind turbulence. Conversely, one can deduce properties of the solar wind turbulence from energetic particle observations. In this article I briefly review some of the current state of knowledge of particle acceleration and transport in the inner heliosphere and discuss a few topics which may bear the key features to further understand the problem of particle acceleration and transport. 相似文献
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Ludmila Třísková Pavel Šroubek Igor S. Veselovskij 《Studia Geophysica et Geodaetica》1992,36(1):57-59
Summary The vortex flow pattern in the outer heliosphere is calculated on the basis of hydrodynamical equations. Quantitative solution in cylindrical coordinates is used. Moving vortices may be formed due to the heliolatitudinal solar wind velocity dependence and nonstationary boundary conditions near the Sun. The flow pattern consists of a system of cyclones and anticyclones. 相似文献
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D. V. Erofeev 《Geomagnetism and Aeronomy》2013,53(7):822-826
Compressible fluctuations in solar wind plasma are analyzed on the basis of the 1995–2010 WIND and Advanced Composition Explorer (ACE) spacecraft data. In the low-speed solar wind (V 0 < 430 km/s), correlations between fluctuations in the magnetic field direction and plasma density, as well as between velocity fluctuations and plasma density, are found. The covariance functions of these parameters calculated as functions of the local magnetic field direction are axially symmetric relative to the axis, which is oriented nearly along the regular magnetic field of the heliosphere (the Parker spiral). Fluctuations in the magnetic field and velocity are polarized in the plane that is orthogonal to the axis of symmetry. Plasma oscillations of these properties can be caused by fast magnetosonic waves propagating from the Sun along the Parker spiral. 相似文献
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《Journal of Atmospheric and Solar》2000,62(16):1527-1543
Co-ordinated observations of the Sun and inner heliosphere using a large number of space- and ground-based instruments were carried out in August–September 1996, August 1998 and August–September 1999 as the first, second and third Whole Sun Months. These observations provided unprecedented cover of the Sun and inner heliosphere at solar minimum (1996) and during the rising phase of the new solar cycle (1998, 1999). In this paper we review the observations made during the three Whole Sun Months and consider the changes in the large-scale structure of the heliosphere seen over the four years. 相似文献
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S. Asenovski 《Geomagnetism and Aeronomy》2017,57(8):973-977
The heliospheric current sheet (HCS) is modified by the solar activity. HCS is highly inclined during solar maximum and almost confined with the solar equatorial plane during solar minimum. Close to the HCS solar wind parameters as proton temperature, flow speed, proton density, etc. differ compared to the region far from the HCS. The Earth’s magnetic dipole field crosses HCS several times each month. Considering interplanetary coronal mass ejections (ICME) and high speed solar wind streams (HSS) free periods an investigation of the HCS influence on the geomagnetic field disturbances is presented. The results show a drop of the Dst index and a rise of the AE index at the time of the HCS crossings and also that the behavior of these indices does not depend on the magnetic polarity. 相似文献
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《Journal of Atmospheric and Solar》1999,61(15):1093-1109
Based on total ozone data from the World Ozone Data Center and stratospheric geopotential height data from the Meteorological Institute of Berlin Free University for the months of January through March for the time period of 1958–1996, the influence of the 11-year solar cycle and the equatorial quasi-biennial oscillation (QBO) on total ozone and the stratospheric circulation at 30 hPa over Northern Europe is investigated. The analysis is performed for different levels of solar activity. The relationship of the equatorial QBO with ozone and the stratospheric circulation over the study region exhibits unique features attributed to strong opposite connections between the equatorial zonal wind and ozone/stratospheric dynamics during periods of solar minimum and maximum. Using the Solar/QBO effect, a statistical extraction of the interannual variations of total ozone and stratospheric circulation over Northern Europe has been attempted. The variations extracted and observed for late winter show very good correspondence. The solar/QBO effect in total ozone and stratospheric dynamics over Northern Europe appears to be related to planetary wave activity. 相似文献
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It has been indicated that the cross section of the streamer belt in the solar corona and its extension in the heliosphere—heliospheric plasma sheet (HPS)—have the form of two radially oriented closely located (at a distance of d ≈ 2.0–2.5° in the heliocentric coordinate system) rays with increased and generally different densities. The angular dimensions of the rays are ≈d. The neutral line of the magnetic field in the corona and the related sector boundary in the Earth’s orbit are located between the peaks of densities of these two rays. In the events, during which the true sector boundary coincides with the heliospheric current sheet, the transverse structure of the streamer belt in the heliosphere (or the HPS structure) is quasistationary; i.e., this structure slightly changes when the solar wind moves from the Sun to the Earth in, at least, 50% of cases. A hypothesis that a slow solar wind, flowing in the rays with increased density of the streamer belt, is probably generated on the Sun’s surface rather than at the top of the helmet, as was assumed in [Wang et al., 2000], is put forward. 相似文献
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D. V. Erofeev 《Geomagnetism and Aeronomy》2017,57(7):864-868
We consider a model that couples the magnetic field fluctuations in the heliosphere with random shifts of force line footpoints on the Sun. This model generalizes the Giacalone (2001) model by taking into account the large-scale inhomogeneity of the solar wind velocity. This generalization aims to explain a number of specific features of the distribution of IMF directions, such as the change in the asymmetry of the distribution of IMF directions as a function of heliographic latitude and the solar cycle phase and the correlation of azimuthal angles and inclinations of the IMF; the sign of this correlation changes during the solar magnetic cycle. The simulation results have shown that the gradients of the solar wind speed can actually explain these specific features of the distribution of IMF directions, at least qualitatively. 相似文献
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An extended structure-function model is developed by including the new effect in the p-model of Meneveau and Sreenivasan which shows that the averaged energy cascade rate changes with scale, a situation which has been found to prevail in nonfullydeveloped turbulence in the inner solar wind. This model is useful for the small-scale fluctuations in the inner heliosphere, where the turbulence is not fully developed and cannot be explained quantitatively by any of the previous intermittency turbulence models. With two model parameters, the intrinsic index of the energy spectrum <alpha>, and the fragmentation fraction P 1, the model can fit, for the first time, all the observed scaling exponents of the structure functions, which are calculated for time lags ranging from 81 s to 0.7 h from the Helios solar wind data. From the cases we studied we cannot establish for P 1 either a clear radial evolution trend, or a solar-wind-speed or stream-structure dependence or a systematic anisotropy for both the flow velocity and magnetic field component fluctuations. Generally, P 1 has values between 0.7 and 0.8. However, in some cases in low-speed wind P 1 has somewhat higher values for the magnetic components, especially for the radial component. In high-speed wind, the inferred intrinsic spectral indices (<alpha>) of the velocity and magnetic field components are about equal, while the experimental spectral indices derived from the observed power spectra differ. The magnetic index is somewhat larger than the index of the velocity spectrum. For magnetic fluctuations in both high- and low-speed winds, the intrinsic exponent <alpha> has values which are near 1.5, while the observed spectral exponent has much higher values. In the solar wind with considerable density fluctuations near the interplanetary current sheet near 1 AU, it is found that P 1 has a comparatively high value of 0.89 for V x . The impact of these results on the understanding of the nature of solar wind fluctuations is discussed, and the limitations in using structure functions to study intermittency are also described. 相似文献
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利用新近获得的子午面磁盔-电流片背景太阳风稳态解,对激波从盔底沿电流片方向往外传播时与磁盔间的相互作用进行了数值模拟研究,重要新结果是:1.磁盔的存在使受扰介质速度跃变中央出现下凹,随着激波传出磁盔区并沿电流片方向传播,速度下凹逐渐减弱以致消失;2.激波将磁盔拉长并把盔顶的环形(垂直赤道面)磁场带到行星际空间,成为行星际磁场南向分量的来源之一;3.5个太阳半径(R⊙)内的磁盔部分将出现精细结构,沿盔外边界形成两条高速带,以及马蹄形密度(亮)环形结构等.这些结果表明,太阳附近高速等离子体与磁盔间存在重要的动力学相互作用过程,对行星际空间的太阳风三维结构有重要影响. 相似文献
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利用新近获得的子午面磁盔-电流片背景太阳风稳态解,对激波从盔底沿电流片方向往外传播时与磁盔间的相互作用进行了数值模拟研究,重要新结果是:1.磁盔的存在使受扰介质速度跃变中央出现下凹,随着激波传出磁盔区并沿电流片方向传播,速度下凹逐渐减弱以致消失;2.激波将磁盔拉长并把盔顶的环形(垂直赤道面)磁场带到行星际空间,成为行星际磁场南向分量的来源之一;3.5个太阳半径(R⊙)内的磁盔部分将出现精细结构,沿盔外边界形成两条高速带,以及马蹄形密度(亮)环形结构等.这些结果表明,太阳附近高速等离子体与磁盔间存在重要的动力学相互作用过程,对行星际空间的太阳风三维结构有重要影响. 相似文献
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During the prolonged and deep minimum of solar activity between cycles 23 and 24, an unusual behavior of the heliospheric characteristics and increased intensity of galactic cosmic rays (GCRs) near the Earth’s orbit were observed. The maximum of the current solar cycle 24 is lower than the previous one, and the decline in solar and, therefore, heliospheric activity is expected to continue in the next cycle. In these conditions, it is important for an understanding of the process of GCR modulation in the heliosphere, as well as for applied purposes (evaluation of the radiation safety of planned space flights, etc.), to estimate quantitatively the possible GCR characteristics near the Earth in the upcoming solar minimum (~2019–2020). Our estimation is based on the prediction of the heliospheric characteristics that are important for cosmic ray modulation, as well as on numeric calculations of GCR intensity. Additionally, we consider the distribution of the intensity and other GCR characteristics in the heliosphere and discuss the intercycle variations in the GCR characteristics that are integral for the whole heliosphere (total energy, mean energy, and charge). 相似文献
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We investigate the inclinations of heliospheric current sheet at two sites in interplanetary space, which are generated from the same solar source. From the data of solar wind magnetic fields observed at Venus (0.72 AU) and Earth (1 AU) during December 1978–May 1982 including the solar maximum of 1981, 54 pairs of candidate sector boundary crossings are picked out, of which 16 pairs are identified as sector boundaries. Of the remainder, 12 pairs are transient structures both at Venus and Earth, and 14 pairs are sector boundaries at one site and have transient structures at the other site. It implies that transient structures were often ejected from the coronal streamer belt around the solar maximum. For the 16 pairs of selected sector boundaries, we determine their normals by using minimum variance analysis. It is found that most of the normal azimuthal angles are distributed between the radial direction and the direction perpendicular to the spiral direction both at Venus and Earth. The normal elevations tend to be smaller than ≈45° with respect to the solar equatorial plane, indicating high inclinations of the heliospheric current sheet, in particular at Earth. The larger scatter in the azimuth and elevation of normals at Venus than at Earth suggests stronger effects of the small-scale structures on the current sheet at 0.72 AU than at 1 AU. When the longitude difference between Venus and Earth is small (<40° longitudinally), similar or the same inclinations are generally observed, especially for the sector boundaries without small-scale structures. This implies that the heliospheric current sheet inclination tends to be maintained during propagation of the solar wind from 0.72 AU to 1 AU. Detailed case studies reveal that the dynamic nature of helmet streamers causes variations of the sector boundary structure. 相似文献
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The tropical cyclones form over the oceanic regions where conventional meteorological observations are not available. This
contributes to a poor initial analysis of the cyclonic vortex and hence inadequate forecast. One way of overcoming the above
problem is to modify the initial analysis by replacing the weak and ill-defined vortex in the initial analysis with a synthetic
vortex having the correct size and intensity at the correct location. In this study we are investigating the effect of inclusion
of a synthetic vortex based on Rankine as well as on Holland wind profiles, using NCAR-AFWA bogussing scheme for the prediction
of four tropical cyclones, which formed over the Bay of Bengal during November 2002 and 2005, December 2005 and over the Arabian
Sea during May 2004, using the MM5 model. Two numerical experiments are designed in this study for each of the above four
cyclones. In the first experiment the model is integrated with a synthetic vortex based on Rankine wind profile while in the
second experiment we utilize the Holland wind profile. For the November 2002 cyclone, in both the experiments the model is
integrated from 10 November 2002 18 UTC to 12 November, 2002 12 UTC with the synthetic vortex inserted at the initial time.
The results of the study for the November 2002 cyclone show that the model simulation with the Holland vortex has produced
a stronger cyclone in terms of minimum sea-level pressure and maximum wind speed. Also, the results for the November 2002
cyclone with the Holland vortex showed a better longitudinal height section of the horizontal wind speed across the center
of the cyclone. The track error of the cyclone for the November 2002 cyclone is less in the model simulation with the Holland
vortex at the initial time and at 24 hours of forecast. The results for the November 2002 cyclone with the Rankine vortex
showed greater vertical wind speed as compared to the Holland vortex. However, for the November 2002 cyclone there were no
significant differences in the spatial distribution of precipitation for both the experiments. In order to provide an adequate
number of case studies for a good statistical sample, the present study is extended for three additional cyclones over the
Indian region. All four cyclones studied here show that the Holland vortex has produced a stronger cyclone in terms of the
minimum sea-level pressure and maximum wind speed. The Holland vortex showed a better vertical structure of wind speed in
the longitudinal height section at 24 hours of forecast for the November 2005 cyclone while the structure was better for the
Rankine vortex for the remaining two cyclones. There were no significant differences in the spatial distribution of precipitation
for the two experiments corresponding to all four cyclones. Some statistical results pertaining to all four cyclones are provided
such as the average track error as well as the average difference between the observed and the model minimum sea-level pressure
and the maximum wind speed. The statistical results corresponding to the average of all the four cyclones are at only a slight
variance with the results corresponding to the November 2002 cyclone. 相似文献