日面方位磁场扰动和行星际磁场螺旋结构

文采用球坐标下2.5维理想MHD模型，对日球子午面内方位磁场扰动的传播进行数值模拟，重点分析它对行星际磁场螺旋角的影响. 本文认为，观测到的行星际磁场螺旋角大于Parker模型的预言值，是太阳表面不断向行星际发出同向方位磁场扰动的结果；太阳较差自转在太阳内部产生的方位磁场为这类扰动提供了源头. 模拟结果表明，采用持续时间等于周期的十分之一、扰动幅度为103nT量级的正向方位磁场扰动，就可使1 AU处行星际磁场的螺旋角增加2°左右，与有关观测结果相符. 模拟结果还表明，上述方位磁场扰动对日球子午面内的太阳风特性和磁场位形的影响基本上可以忽略.

Azimuthal magnetic field disturbances and spiral structure of the interplanetary magnetic field

A 2.5 dimensional, ideal MHD model in spherical coordinates is used to numerically simulate the propagation of azimuthal magnetic field disturbances with emphasis upon its influence on the spiral angle of the interplanetary magnetic field (IMF). The observed fact that the IMF spiral angle is larger than that predicted by the Parker model is attributed to a ceaseless launching of azimuthal magnetic field disturbances of the same sign from the solar surface. The differential rotation of the Sun induces an azimuthal magnetic field inside the Sun, providing a source for these disturbances. The simulation results show that azimuthal magnetic field disturbances of the same sign which have a duration of one tenth of the period and an amplitude of order of 103nT is capable of increasing the IMF spiral angle at 1AU by 2° so as to match with relevant observations. It is also shown that the azimuthal magnetic field disturbances mentioned above have little effect on the solar wind properties and the magnetic configuration in the heliospheric meridional plane.