子午面内Alfvén波的传播特征

本文使用由ＷＫＢ近似得到的Ａｌｆｖｅｎ波传播的张量表达式,具体计算和讨论了一种太阳子午面内含盔形－电流片磁位形的流场中Ａｌｆｖｅｎ波的传播特征,主要结果是：（１）Ａｌｆｖｅｎ波磁场起伏随日心距离的增加而衰减,其中极开区的衰减远快于赤道区,但随着距离的增大,这种纬度关系将迅速变弱,以致在较远空间,磁起伏相差很小,衰减很慢;（２）Ａｌｆｖｅｎ波的相对磁场起伏ｂ／Ｂ随着距离的增加而迅速增大,在几个太阳半径之后变化不再明显,达到所谓的＂饱和＂;在大日心距离的盔形电流片附近,Ａｌｆｖｅｎ波将成为重要的磁场组成部分;（３）Ａｌｆｖｅｎ波速度起伏纬度关系较为明显,相对速度起伏。ｕ／Ｕ随着距离增大而衰减,电流片区衰减得较快,但这种纬度差别将变弱．与黄道面内Ａｌｆｖｅｎ波传播特征的具体比较表明,磁场涨落的变化特征与背景场位形存在着十分密切的关系,但速度涨落与背景场没有这种明显关系．

PROPAGATION OF ALFVEN WAVES IN HELIOSPHERIC MERIDIAN

Using the WKB solutions of incompressible Alfven waves, it is investigated that the propagation of Alfven waves in the background solar wind with a helmet-shaped current sheet obtained by a time-dependent, two dimensional MHD numerical simulation. The results show that: (1) With increasing heliospheric distance, the Alfvenic magnetic amplitude b will decay Tepidly. Near the heliospkeric sheet, the more slowly of the decay, so that the amplitude of b is almost equal everywhere at large distances. (2) Within several solar radii, the velocity fluctuations reach rapidly the maximum at all latitudes, and after that begin to decay gradualy with increasing distances. At large distances the amplitUde of u over solar polar is a little larger than near the current sheet. (3) With increasing heliospheric distance, the relative magnetic field b/B will rise. Over the solar polar the b/B will increase much more slowly than near the current sheet, but above several solar radii, the values of b/B at all latitudes will no longer increase obviously with increasing distance, that is to say, the evolution of the flutuations will reach the so called "saturations", this result may be an important support for Alfven wave acceleration of the solar wind. Another important result is that near the heliospheric current sheet, b/B De 1 so that Alfvenic fluctuations will be main maglletic field compositions at large distance regions. (4) Near the heliospheric current sheet, the values of the relative velocity fluctuation u/U are the largest and decrease most repidly, instead u/U varies vety slowly over the polar. Within several solar radii, the u/U at all latitudes rapidly becomes vary small, after that at almost same slope and same value, decreases very slowly with increasing distance. Above results show firstly that the propagation nature of polar Alfven waves is different to that near the heliospheric current sheet.