Magnetohydrodynamic Phenomena in the Sun and Solar Wind

该基金将支持3个领域的理论研究：太阳磁场是由太阳内部的水力发电机不断再生和重新配置的。磁场以薄通量绳和活动区域的形式出现在地表。内部磁场的强度和拓扑结构不能直接观测到；它分裂成通量管的深度也不确定。然而，通过计算场对声波振荡频率的影响，可以利用日震学来约束内部场的性质。磁场来自光球层，在日冕的结构和能量学中起着主导作用。能量通过光球运动储存在磁场中；这些运动可能导致电流片的形成。这些电流片的耗散会以一种不均匀的或断断续续的方式加热日冕，这种方式被低分辨率观测所掩盖。储存在磁场中的能量也可以通过磁流体动力学的不稳定性释放出来。磁场也在日冕和日球层中激波的起源和传播中起作用。冲击可以加速粒子；由此产生的非热粒子分布对波的生长是不稳定的，这改变了上游介质，使激波演变。这些观点可以解释观测到的太阳风冲击的演化。以上都与日地关系密切相关；磁场的起源、日冕的加热和冲击的传播都对地球环境产生影响。

This grant will support theoretical research in 3 areas, - The solar magnetic field is continuously regenerated and reconfigured by a hydromagnetic dynamo in the solar interior. The field emerges at the surface in the form of thin flux ropes and active regions. The strength and topology of the interior field are not directly observable; neither is the depth at which it fragments into flux tubes. However, by computing the effect of the field on the acoustic oscillation frequencies it is possible to use helioseismology to constrain the properties of the interior field. The magnetic field emerges from the photosphere and plays a dominant role in the structure and energetics of the solar corona. Energy is stored in the field by photospheric motions; these motions may cause current sheets to develop. Dissipation of these current sheets can heat the corona in a patchy or episodic fashion which is masked by low resolution observations. Energy stored in the field can also be released by magnetohydrodynamic instabilities. The magnetic field also plays a role in the origin and propagation of shock waves in the corona and heliosphere. Shocks can accelerate particles; the resulting nonthermal particle distribution can be unstable to the growth of waves, which modify the upstream medium so that the shock evolves. These ideas may explain observed evolution of shocks in the solar wind. All of the above is very relevant to solar terrestrial relations; the origin of the magnetic field, the heating of the corona and the propagation of the shocks all have impact on the terrestrial environment.