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231.
In previous publications (Keppens et al.: 2002, Astrophys. J. 569, L121; Goedbloed et al.: 2004a, Phys. Plasmas
11, 28), we have demonstrated that stationary rotation of magnetized plasma about a compact central object permits an enormous
number of different MHD instabilities, with the well-known magneto-rotational instability (Velikhov, E. P.: 1959, Soviet Phys.–JETP Lett. 36, 995; Chandrasekhar, S.: 1960, Proc. Natl. Acad. Sci. U.S.A. 46, 253; Balbus, S. A. and Hawley, J. F.: 1991, Astrophys. J. 376, 214) as just one of them. We here concentrate on the new instabilities found that are driven by transonic transitions of
the poloidal flow. A particularly promising class of instabilities, from the point of view of MHD turbulence in accretion
disks, is the class of trans-slow Alfv’en continuum modes, that occur when the poloidal flow exceeds a critical value of the slow magnetosonic speed. When this happens, virtually
every magnetic/flow surface of the disk becomes unstable with respect to highly localized modes of the continuous spectrum.
The mode structures rotate, in turn, about the rotating disk. These structures lock and become explosively unstable when the
mass of the central object is increased beyond a certain critical value. Their growth rates then become huge, of the order
of the Alfv’en transit time. These instabilities appear to have all requisite properties to facilitate accretion flows across
magnetic surfaces and jet formation. 相似文献
232.
Soft X-ray (SXR) waves, EIT waves, and Hα Moreton waves are all associated with coronal mass ejections (CMEs). The knowledge of the characteristics about these waves is crucial for the understanding of CMEs, and hence for the space weather researches. MHD numerical simulation is performed, with the consideration of the quiet Sun atmosphere, to investigate the CME/flare processes. On the basis of the numerical results, SXR, EUV, and Hα images of the eruption are synthesized, where SXR waves, EIT waves, and Hα Moreton waves are identified. It confirms that the EIT waves, which border the expanding dimmming region, are produced by the successive opening (or stretching) of the closed magnetic field lines. Hα Moreton waves are found to propagate outward synchronously with the SXR waves, lagging behind the latter spatially by ~27 Mm in the simulated scenario. However, the EIT wave velocity is only a third of the Moreton wave velocity. The synthesized results also suggest that Hα± 0.45Å would be the best off-band for the detection of Hα Moreton waves. 相似文献
233.
B. Schmieder P. DémoulinG. Aulanier 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2013
Solar filament eruptions play a crucial role in triggering coronal mass ejections (CMEs). More than 80% of eruptions lead to a CME. This correlation has been studied extensively during the past solar cycles and the last long solar minimum. The statistics made on events occurring during the rising phase of the new solar cycle 24 is in agreement with this finding. Both filaments and CMEs have been related to twisted magnetic fields. Therefore, nearly all the MHD CME models include a twisted flux tube, called a flux rope. Either the flux rope is present long before the eruption, or it is built up by reconnection of a sheared arcade from the beginning of the eruption. 相似文献
234.
The surface wave induced magnetic reconnection (SWIMR) model based on Alfven Resonance theory will be discussed briefly both
for collisional and collisionless plasmas. It is shown that the spatial scales and time delays associated with Flux Transfer
Events and Pulsed Ionospheric Flows, as observed by satellites and SuperDARN radars and the magnetic bubbles, observed at
the high latitude boundary of the magnetopause, can be explained by the SWIMR model.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
235.
One of the most ubiquitous indicators of the state and topology of the magnetosphere are ultra-low frequency (ULF) waves.
These may be continuously and inexpensively monitored from the ground using networks of magnetometers. The most robust measurable
quantity provided by magnetometer networks is signal phase and this paper emphasizes the usefulness of this parameter in a
variety of ULF wave diagnostic processes ranging from equatorial to high latitudes.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
236.
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
237.
238.
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
239.
Magneto-gravity Waves Trapped in the Lower Solar Corona 总被引:1,自引:0,他引:1
Yu-Qing Lou 《Space Science Reviews》1999,87(1-2):261-264
The possibility of trapped magneto-gravity waves in the lower solar corona with an open magnetic field is discussed. Intensity
variations and/or Doppler shifts of relevant UV, EUV and x-ray spectral lines in the chromosphere, transition region and lower
corona may reveal the existence of such low-frequency modes (with periods longer than ∼ 1.5 hour). The spectrum may be either
discrete or continuous depending on the reflection property of the narrow transition region. These modes can be utilized to
probe the dynamics of the upper chromosphere, transition region and lower corona; they may also play an important role in
coronal heating.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
240.
介绍了一种斜边占π/5的等腰梯形脉宽调制波,从理论上证明了采用这种PWM(PulseWidth Modulation)波控制的变频器,能消除输出电压的5次谐波分量,使输出电压谐波分量小,电流波形好,系统运行时转矩脉动小,可靠、平稳、噪声低.已将这种控制技术应用于某种列车风扇异步电机的变频调速,实验结果与理论分析相吻合. 相似文献