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81.
R. Rodríguez-Gasén A. Aran B. Sanahuja C. Jacobs S. Poedts 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2011
The shape of flux profiles of gradual solar energetic particle (SEP) events depends on several not well-understood factors, such as the strength of the associated shock, the relative position of the observer in space with respect to the traveling shock, the existence of a background seed particle population, the interplanetary conditions for particle transport, as well as the particle energy. Here, we focus on two of these factors: the influence of the shock strength and the relative position of the observer. We performed a 3D simulation of the propagation of a coronal/interplanetary CME-driven shock in the framework of ideal MHD modeling. We analyze the passage of this shock by nine spacecraft located at ∼0.4 AU (Mercury’s orbit) and at different longitudes and latitudes. We study the evolution of the plasma conditions in the shock front region magnetically connected to each spacecraft, that is the region of the shock front scanned by the “cobpoint” (Heras et al., 1995), as the shock propagates away from the Sun. Particularly, we discuss the influence of the latitude of the observer on the injection rate of shock-accelerated particles and, hence, on the resulting proton flux profiles to be detected by each spacecraft. 相似文献
82.
B. Van der Holst S. Poedts E. Chané C. Jacobs G. Dubey D. Kimpe 《Space Science Reviews》2005,121(1-4):91-104
Simulations of coronal mass ejections (CMEs) evolving in the interplanetary (IP) space from the Sun up to 1 AU are performed
in the framework of ideal magnetohydrodynamics (MHD) by the means of a finite-volume, explicit solver. The aim is to quantify
the effect of the background solar wind and of the CME initiation parameters, such as the initial magnetic polarity, on the
evolution and on the geo-effectiveness of CMEs. First, three different solar wind models are reconstructed using the same
numerical grid and the same numerical scheme. Then, different CME initiation models are considered: Magnetic foot point shearing
and magnetic flux emergence. For the fast CME evolution studies, a very simple CME model is considered: A high-density and
high-pressure magnetized plasma blob is superposed on a background steady state solar wind model with an initial velocity
and launch direction. The simulations show that the initial magnetic polarity substantially affects the IP evolution of the
CMEs influencing the propagation velocity, the shape, the trajectory (and thus, the geo-effectiveness). 相似文献
83.
Hongang Yang Shuping Jin Chaoxu Liu 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2008,41(10):1649-1657
An uniform out-of-plane magnetic field component By0 is added to the equilibrium Harris sheet with plasma β = 0.5 and Lc = 0.5di (where Lc is the half-width of the equilibrium current layer and di is the ion inertial length). Driven by the continuous boundary inflows, the magnetic reconnections with the guide field By0/B0 ranging from 0 to 4.0 are investigated using a 2.5D Hall magnetohydro-dynamic (MHD) code developed from a multi-step implicit scheme. The features of the reconnection field are substantially altered in the presence of the guide field. The openness of the magnetic separatrix angle is slightly reduced and the anti-symmetric quadrupolar structure of By field and the symmetric distribution of plasma pressure P are replaced by an asymmetric By four-wing structure and an asymmetric P plot as a non-zero By0 is added. The decoupling of electrons and ions also occurs near the X line in the case with a finite By0, but the effect of initial By0 on the electron flow is greater than that on the ion flow. The reconnection rates at the X-line drops from 0.151 to 0.06, namely, ∂A/∂t is reduced by a factor of 2.5 as By0/B0 increases from 0 to 4.0. The reduction of reconnection rate might be related to the reducing openness of reconnection layer with the increasing By0. 相似文献
84.
A.M. Gulisano S. Dasso C.H. Mandrini P. Dmoulin 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2007,40(12):1881-1890
Magnetic clouds (MCs) are highly magnetized plasma structures that have a low proton temperature and a magnetic field vector that rotates when seen by a heliospheric observer. More than 25 years of observations of magnetic and plasma properties of MCs at 1 AU have provided significant knowledge of their magnetic structure. However, because in situ observations only give information along the trajectory of the spacecraft, their real 3D magnetic configuration remains still partially unknown. We generate a set of synthetic clouds, exploring the space of parameters that represents the possible orientations and minimum distances of the satellite trajectory to the cloud axis, p. The synthetic clouds have a local cylindrical symmetry and a linear force-free magnetic configuration. From the analysis of synthetic clouds, we quantify the errors introduced in the determination of the orientation/size (and, consequently, of the global magnetohydrodynamic quantities) by the Minimum Variance method when p is not zero. 相似文献
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88.
对低磁雷诺数近似下流向磁场作用的二维磁流体槽道湍流进行了直接数值模拟(DNS,Direct Numerical Simulation),给出了 Re=10 000时不同磁相互作用数下二维磁流体槽道湍流的近壁速度分布、湍流脉动速度均方根、雷诺应力等统计量的变化,并与中性流体二维槽道湍流进行了比较.结果表明:流向磁场作用会导致对数区上移;雷诺应力最大值随磁相互作用数呈线性变化;随着磁相互作用数的增大,下壁面平均涡量的时间演化由拟周期性向周期性转变,且脉动周期逐渐增大并当流动层流化后下壁面平均涡量成为常值. 相似文献
89.
G. Li G. Qin Q. Hu B. Miao 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2012
A puzzling observation of solar wind MHD turbulence is the often seen Kolmogorov scaling of k-5/3, even though the solar wind MHD turbulence is dominated by Alfvénic fluctuations. Recently Li et al. (2011) proposed that the presence of current sheets may be the cause of the Kolmogorov scaling. Here, using a cell model of the solar wind we examine the effect of current sheets on the power spectrum of the solar wind magnetic field. We model the solar wind as multiple cells separated by current sheets. We prescribe the spectra of turbulent magnetic field in individual cells as IK-like and examine the spectra along trajectories that cross multiple boundaries. We find that these spectra become softer and are consistent with the Kolmogorov-scaling. Our finding supports our recent proposal of Li et al. (2011). 相似文献
90.