A Magnetohydrodynamic Simulation of the Interaction between the Solar Wind and Comet Halley

采用三维含时磁流体动力学（MHD）方法模拟了太阳风与彗星气体等离子体的相互作用。该模型再现了最近对哈雷彗星的探测所观察到的几个特征：在彗星前方3.2x10^5公里处有一个微弱的弓形激波。磁场在这个弱弓形激波上增加了3.7倍，并继续增加到接触面（B_<max>/B_<IMF>= 6-8）。等离子体温度在弓形激波处升高，在彗星附近降低。行星际磁场（IMF）谱线悬挂在彗星上，形成一条较长的等离子体尾，其波瓣场很强，B<lobe>/B为<IMF>-5。当太阳风或IMF动压发生变化时，在等离子体尾部形成类射线结构和高等离子体团，并以局部Alfven速度向尾部传播。这些结果解释了用大量照片观测到的彗尾动力学现象。我们对太阳风-彗星相互作用的全球MHD模拟，明确了彗星质量载荷的作用，并与太阳风与其他行星的相互作用进行了比较，给出了重要的启示。

The interaction between the solar wind and the plasmas produced form cometary gases has been modeled by using a three-dimensional time-dependent magneto-hydrodynamic (MHD) simulation with the cometary mass loading. The model reproduced several features observed by the recent missions to comet Halley.A weak bow shock was located 3.2x10^5 km in front of the comet. The magnetic field increased by a factor of 3.7 across this weak bow shock and continued to increase up to the contact surface (B_<max>/B_<IMF>= 6-8). The plasma temperature increased across the bow shock and decreased nearer to the comet. Interplanetary magnetic field (IMF) lines were hung up on the comet and formed a long plasma tail in which the lobe field was quite strong and B_<lobe>/B_<IMF>-5. A cold dense plasma sheet formed in the tail and this thin plasma sheet was oriented normal the IMF direction.Ray-like structure and a plasmoid with high plasma pressure are formed in thecometary plasma tail and propagate tailward with a local Alfven speed, when the dynamic pressure of solar wind or the IMF changes. These results give an explanation on the dynamics of cometary tail which were shown by the observationsusing a lot of photos. Our global MHD simulation in the solar wind-comet interaction has made clear the role of cometary mass loading and also has given animportant incitement in comparison with the interaction between the solar wind and other planets.