Study on collision between a current loop and a plasma cloud in solar flares

等离子体天体物理学尚未解决的一个重要问题是太阳耀斑期间释放的磁场能量如何转化为等离子体加热和高能粒子加速。YOHKOH卫星观测到的一个新的耀斑，即所谓的masuda -耀斑，在硬x射线源的软x射线图像中显示出一个环状结构，该结构位于软x射线环顶部上方。为了解释这种耀斑，Masuda等人提出了一个模型，认为这种耀斑是由电流环和等离子体云之间的相互作用引起的。(1)为了解释本次耀斑观测到的x射线源，我们利用三维MHD码和三维粒子码研究了电流环与等离子体云的碰撞过程，明确了等离子体加热过程和高能电子加速机制。(2)利用三维MHD模拟研究了x型电流环碰撞的聚结过程，并与1993年8月2日发生的一次典型x型耀斑进行了比较。结果表明，观测值与模拟值吻合较好。(3)复合效应对色球中的重联过程起着重要作用。利用复合效应的MHD模拟研究了这一效应。结果表明，在色球层磁重联过程中，复合效应极大地增强了等离子体的加热。(4)研究了弱电离等离子体中Alfven波的非线性行为，表明Alfven波的调制不稳定性对等离子体局部加热有重要影响。结果应用于太阳色球加热。

One of important unsolved problems in Plasma Astrophysics is how the magnetic field energy released during a solar flare can be converted to plasma heating as well as high energy particle acceleration.A new flare observed by the YOHKOH sattelite, which is so called as Masuda-flare showed a loop structure in the soft X-ray image with hard X-ray source, which location is just above the soft X-ray loop top. To explain this flare, Masuda et al.proposed a model that this flare was caused by the interaction between a current loop and a plasmoi(plasma cloud).(1) In order to explain the X-ray source observed in this flare, we investigated the collision process between a current loop and a plasma cloud by using 3-D MHD code and 3-D particle code, and made clear the plasma heating process and the mechanism of high energy electron acceleration.(2) We investigated the coalescence process of X-type current loop collision by 3-D MHD simulation and compared with a typical X-type flare on the 1993, Aug.2. The result showed a good agreement on the temperature variation between the observation and the simulation.(3) The recombination effect becomes important for the reconnection process in the chromosphere. This effect was investigated by the MHD simulation with recombination effect. It has been shown that the recombination effect greatly enhances the plasma heating during the magnetic reconnection in the chromosphere.(4) The nonlinear behavior of Alfven waves in weakly ionized plasmas was investigated and it was shown that the modulational instability of the Alfven waves is important for the local plasma heating. The results were applied to the solar chromospheric heating.