An analytical model of prominence dynamics

Solar prominences are magnetic structures incarcerating cool and dense gas in an otherwise hot solar corona. Prominences can be categorized as quiescent and active. Their origin and the presence of cool gas ($～{10}^4$?K) within the hot ($～{10}^6\text{K}$) solar corona remains poorly understood. The structure and dynamics of solar prominences was investigated in a large number of observational and theoretical (both analytical and numerical) studies. In this paper, an analytic model of quiescent solar prominence is developed and used to demonstrate that the prominence velocity increases exponentially, which means that some gas falls downward towards the solar surface, and that Alfvén waves are naturally present in the solar prominences. These theoretical predictions are consistent with the current observational data of solar quiescent prominences.     

Alfvén wave heating

This review discusses Alfvén wave heating in non-uniform plasmas as a possible means for explaining the heating of the solar corona. It focusses on recent analytical results that enable us to understand the basic physics of Alfvén wave heating and help us with the interpretation of results of numerical simulations. First we consider the singular wave solutions that are found in linear ideal MHD at the resonant magnetic surface where the frequency of the wave equals the local Alfvén frequency. Next, we use linear resistive MHD for describing the waves in the dissipative region and explain how dissipation modifies the singular solutions found in linear ideal MHD.     

Absolute and Convective Instabilities of Circularly Polarized Alfvén Waves

We discuss the recent progress in studying the absolute and convective instabilities of circularly polarized Alfvén waves (pump waves) propagating along an ambient magnetic field in the approximation of ideal magnetohydrodynamics (MHD). We present analytical results obtained for pump waves with small dimensionless amplitude a, and compare them with numerical results valid for arbitrary a. The type of instability, absolute or convective, depends on the velocity U of the reference frame where the pump wave is observed with respect to the rest plasma. One of the main results of our analysis is that the instability is absolute when U _l < U < U _r and convective otherwise. We study the dependences of U _l and U _r on a and the ratio of the sound speed to the Alfvén speed b. We also present the results of calculation of the increment of the absolute instability on U for different values of a and b. When the instability is convective (U < U _l or U > U _r) we consider the signalling problem, and show that spatially amplifying waves exist only when the signalling frequency is in two symmetric frequency bands. Then, we write down the analytical expressions determining the boundaries of these frequency bands and discuss how they agree with numerically calculated values. We also present the dependences of the maximum spatial amplification rate on U calculated both analytically and numerically. The implication of the obtained results on the interpretation of observational data from space missions is discussed. In particular, it is shown that circularly polarized Alfvén waves propagating in the solar wind are convectively unstable in a reference frame of any realistic spacecraft.     

MKDVB and CKB Shock Waves

This review presents results from MKDVB and CKB systems to illustrate the properties of magnetohydrodynamics intermediate shock waves. The intermediate shocks can have a family of shock structures; the shock structure and the evolution are related. Furthermore, there exists a class of time-dependent intermediate shocks. This revised version was published online in August 2006 with corrections to the Cover Date.     

磁流体斜激波的汇合

本文讨论磁流体快、慢激波的汇合作用规律,主要结论如下:(1)两个前向快激波汇合之后,形成一更强的前向快激波,尾随一前向慢稀疏波、一正接触间断(后侧密度大于前侧)、一后向慢激波和一后向快稀疏浚。(2)两个前向慢激波汇合之后,形成一更强的前向慢激波,尾随一正接触间断、一后向慢稀疏波和一后向快激波2在前向慢激波前方出现一前向快波,它或为稀疏浚(中、小激波角情况),或为激波(大激波角情况).(3)前向快激波会追上前向慢激波而发生汇合,之后互换位置且强度减弱,尾随一正接触间断和一后向稀疏波对。      

磁层顶剪切磁流体非线性性态的谱截断法研究Ⅰ.流场扰动对磁场的作用

本文用谱截断方法研究了磁层顶剪切磁流体的非线性性态。结果表明:流场扰动会使系统出现剪切不稳定(K-H不稳定)性;系统具有对初值的敏感性,这是导致湍动而使磁层顶动力学性态难以预测的根本原因;流场粘性及流场与磁场的相互作用使能量与动量在流场与磁场中转化和传输;外界能流通过粘性与耦合作用可周而复始地在系统中传递。      

The Solar Wind - Inner Heliosphere

The solar wind in the inner heliosphere, inside ~ 5 AU, has been almost fully characterized by the addition of the high heliographic latitude Ulysses mission to the many low latitude inner heliosphere missions that preceded it. The two major omissions are the high latitude solar wind at solar maximum, which will be measured during the second Ulysses polar passages, and the solar wind near the Sun, which could be analyzed by a Solar Probe mission. Here, existing knowledge of the global solar wind in the inner heliosphere is summarized in the context of the new results from Ulysses.     

一种新的用于MHD方程逆风格式的Jacobian矩阵分裂方法

针对理想MHD方程,提出了一种新的基于MacCormack算法的雅可比矩阵分裂方法,克服了原有方法稳定性差的问题,并成功地应用于理想MHD方程的求解.控制方程在非结构混合网格上进行空间离散,其中对流项采用本文发展的逆风向量分裂格式,并引入了双曲型磁场散度清除技术,时间推进为显式5步龙格-库塔方法.对MHD激波管流动和带均匀磁场干扰的二维高超声速钝头体绕流流场进行了数值模拟,得到了与参考文献相吻合的数值结果,表明本文发展的数值分裂方法可以有效地捕捉MHD流场的流动特征,并且具有比MacCormack方法更高的稳定性和计算精度.     

乘波构型飞行器磁流体进气道一体化概念设计

采用准一维的磁流体方程组对设计状态下内磁流体发生器进行参数设计,利用斜激波理论设计磁流体进气道一体化的外形.以该外形为基点,对安装五对电极的内磁流体发生器采用五方程模型进行三维数值模拟,并通过调节其磁作用数以满足准一维假设下设计的进气道外形.研究表明,磁流体进气道最小出口流动均匀参数可以作为判别内发生器最优磁作用数的准则,在该磁作用数下内磁流体发生器可以有效地提高进气道的性能.      

Three Dimensional Simulation of the Steady Solar Wind in Carrington Rotation 1935

A three-dimensional MHD simulation is conducted to study the steady solar wind in Carrington Rotation (CR) 1935 by using the three-dimensional numerical magnetohydrodynamic (MHD) model introduced by Feng et al. The numerical results demonstrate that the neutral current sheet has two peaks and two valleys, which is consistent with the result of PFSS model at Wilcox Solar Observatory (WSO). The obtained proton number density at 2.5 Rs is of the same order of magnitude as the result estimated from K-coronal brightness during the CRs 1733-1742 in 1983made by Wei et al. The radial velocity profile along heliocentric distance is consistent with that of low solar wind speed deduced by Sheeley and Wang et al. However, it is not able to reproduce the fast-speed flow in coronal holes and slow solar wind in streamers because of oversimplified energy equation adopted in our model. Future efforts must be made to remedy this deficiency.