The 16 August 1999 EUV brightenings are numerically simulated by a third-order upwind compact scheme,basing on the TRACE observation.The present simulation can give a possible explanation to its formation and evolution.The numerical results show that the initial reconnection jets at around X-point are responsible for the occurrence of EUV brightening.The strong and superposed ejections caused by the first and second coalescence of magnetic islands are possibly related to the lifted material which initially appeared as absorption features and Later EUV-emitting structures respectively.The bi-directional reconnection jets may correspond to the lifted material that either continued to move upward along the apparently open field lines or fell down to the surface.
选取了1997．1,-2002．9期间的80个CME-ICME事件，结合太阳光球磁场的观测和CME爆发源的位置，建立了一种用于研究CME传播及其地磁响应的坐标系——电流片磁坐标系CMC（current sheet magnetic coordinate）．在此基础上研究了CME爆发位置以及爆发时刻的日球电流片位形对CME引起的地磁扰动强度（以Dst指数为例）和CME渡越时间的影响，初步结论是：（i）CME的地磁响应存在着关于电流片的同异侧效应，即当地球和CME的爆发源处于电流片的同侧时，CME更易于传播到地球，更易于引起较强的地磁暴，相对而言，异侧的CME事件较少到达地球，它所引起的地磁暴也较弱．（ii）日球电流片到地球的角距离影响相应地磁扰动的强度，电流片越靠近地球位置，相应的地磁扰动越强烈．（iii）CME爆发位置与附近电流片位形对CME到达近地空间的渡越时间也有影响．根据这些结论，提出了一种在CMC坐标系下基于CME的投影速度来预报地磁暴强度及CME渡越时间的经验模式，并利用该方法对80个事件进行了预报试验．结果表明，对于DStmi。≤-50nT的中等磁暴和强磁暴事件来说，59％的事件其磁暴强度相对误差〈30％，而全部事件的渡越时间平均绝对值误差都在10h以下．
A new numerical scheme of 3rd order Weighted Essentially Non-Oscillatory (WENO) type for 2.5D mixed GLM-MHD in Cartesian coordinates is proposed. The MHD equations are modified by combining the arguments as by Dellar and Dedner et al to couple the divergence constraint with the evolution equations using a Generalized Lagrange Multiplier (GLM). Moreover, the magnetohydrodynamic part of the GLM-MHD system is still in conservation form. Meanwhile, this method is very easy to add to an existing code since the underlying MHD solver does not have to be modified. To show the validation and capacity of its application to MHD problem modelling, interaction between a magnetosonic shock and a denser cloud and magnetic reconnection problems are used to verify this new MHD code. The numerical tests for 2D Orszag and Tang's MHD vortex, interaction between a magnetosonic shock and a denser cloud and magnetic reconnection problems show that the third order WENO MHD solvers are robust and yield reliable results by the new mixed GLM or the mixed EGLM correction here even if it can not be shown that how the divergence errors are transported as well as damped as done for one dimensional ideal MHD by Dedner et al.
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 1983 made 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.
Aiming at two intense shock events on October 28 and 29, 2003, this paper presents a two-step method, which combines synoptic analysis of space weather ——“observing” and quantitative prediction ——“palpating”, and then uses it to test predictions. In the first step of “observing”, on the basis of observations of the solar source surface magnetic field, interplanetary scintillation (IPS) and ACE spacecraft, we find that the propagation of the shocks is asymmetric relative to the normal direction of their solar sources, and the Earth is located near the direction of the fastest speed and the greatest energy of the shocks. As the two fast ejection shock events, the fast explosion of coronal mass of the extremely high temperature, the strong magnetic field, and the high speed background solar wind are also helpful to their rapid propagation. In the second step of “palpating”, we adopt a new membership function of the fast shock events for the ISF method. The predicted results show that for the onset time of the geomagnetic disturbance, the relative errors between the observational and the predicted results are 1.8% and 6.7%; and for the magnetic disturbance magnitude, the relative errors are 4.1% and 3.1%, re- spectively. Furthermore, the comparison among the predicted results of our two-step method with those of five other prevailing methods shows that the two-step method is advantageous. The results tell us that understanding the physical features of shock propagation thoroughly is of great importance in improving the prediction precision.
XIE Yanqiong1, 2, 3, WEI Fengsi1, FENG Xueshang1 & ZHONG Dingkun1, 2 1. State Key Laboratory of Space Weather, Center for Space Science and Applied Research, Chinese Academy of Sciences, Beijing 100080, China
This paper summarizes the research results obtained by Chinese scientists and/or through international collaborations during 2004 to 2006. Within the context of COSPAR, the progresses in the studies of the middle and upper atmosphere in China in the past two years are introduced with focusing the developments in facilities and instruments, and the advancements in scientific issues, e.g., dynamics related processes, atmospheric constituents, and the coupling with the lower atmosphere.
CHEN Zeyu LIU Renqiang CHEN Hongbin CHEN Wen LU Daren XU Jiyao HU Xiong
Considerable progress for the study of solar corona physics has been achieved by China's space physics community. It involves the theoretical study of coronal process of solar active phenomena, solar wind origin, acceleration of solar wind and coronal mass ejections, observational and numerical study of these problems and prediction methods of solar eruptive activities (such as flares/CMEs). Here is a brief summary of the progress in this area. Main progress is put upon the following three topics: corona and solar wind, numerical method, prediction method.
This paper reviews the recent studies on the ionospheric weather and climate. As a national report prepared for COSPAR, the works concerned here are limited to those made by Chinese scientists during 2004-2006. The main contents include the sudden ionospheric disturbances, the ionospheric storms, the traveling ionospheric disturbances, ionospheric variability, the annual and semiannual ionospheric variations, the solar cycle ionospheric variations, and the long term ionospheric changes.
