偶极倾角对弓激波日下点距离和尾部张角的影响

Influence of the Dipole Tilt Angle on the Subsolar Standoff Distance and the Tail Flaring Angle of the Bow Shock

通过对IMP 8,Geotail,Magion 4和Cluster 1四颗卫星弓激波穿越数据的统计及拟合分析,定量研究了偶极倾角对弓激波日下点距离和尾部张角的影响.结果表明:弓激波日下点距离随偶极倾角绝对值的增大而增大,且偶极倾角为负值时比其为正值时日下点距离增大的幅度更大;弓激波尾部张角随偶极倾角绝对值增大而减小;当偶极倾角由负变为正的时候,弓激波向地球一侧移动,同时尾部张角增大.研究结果为进一步建立包含偶极倾角效应的弓激波模型奠定了基础.

The Earth＇s bow shock has been found to be affected by the dipole tilt angle. Based on the bow shock crossings of IMP 8, Geotail, Magion 4, and Cluster 1, quantitative analysis has been made to examine the influence of the dipole tilt angle on the subsolar standoff distance and the tail flaring angle of the bow shock by fitting the bow shock shape and location in each range of the data sets after normalizing and classifying the data sets. The results show that the subsolar standoff distance increases as the absolute value of the dipole tilt angle increases, and the negative dipole tilt angle does greater influence on the standoff distance than the positive tilt angle; the flaring angle decreases with the increasing absolute value of the dipole tilt angle; when the dipole tilt angle changes from negative to positive, the bow shock moves to Earth, meanwhile the ftaring angle increases. This study make a good foundation for the bow shock model which will include the effects of the dipole tilt angle.