木卫二尾迹的数值模拟  

Numerical simulation of Europa′s plasma wake

作　　者：卢斌[1] 陈出新[1] 

机构地区：[1]中国科学院近地空间环境重点实验室,中国科学技术大学地球和空间科学学院地球和行星科学系,合肥230026

出　　处：《地球物理学报》2014年第11期3851-3858,共8页Chinese Journal of Geophysics

基　　金：国家自然科学基金项目(41374179;41121003);中国科学院重点方向项目(KZZD-EW-01-4)资助

摘　　要：木卫二在木星磁层中运动,与快速共转的木星磁场相互作用形成木星极光中木卫二的尾迹,此尾迹反映了连续扰动的磁通量管对木星电离层电流注入的过程.本文应用细丝理论对此过程进行数值模拟,未扰动的上游磁通量管经过大约720s的时间与木卫二作用形成角度约为4°且相对于木卫二静止的拉伸磁通量管,随后在磁张力的作用下加速运动.在随后大约2160s的加速时间内,磁通量管的速度逐渐与背景磁力线接近,向木星电离层注入的电流也由9×105 A逐渐衰减至0.以1/e初始电流处认为是可观测的木卫二尾迹限度,则木卫二的尾迹仅大约有一至两个经度,这与哈勃望远镜观测到的木卫二尾迹大小大致相同.木卫二尾迹与木卫一尾迹相比,输送的能量约为2.3×1013J,仅有木卫一的1/10,导致尾迹长度远小于木卫一的尾迹长度.此外,模拟过程中发现木卫二下游的压力槽对磁通量管运动的影响很小,可以忽略.Europa is embedded in Jupiter＇s magnetosphere where a rapidly flowing plasma interacts electromagnetically with Europa. A plasma wake grows in the downstream of Europa＇s orbit meanwhile the induced current is injected into Jupiter＇s ionosphere and leads to the Europa＇s aurora footprint. The main purpose of this paper is numerically simulating the evolution of a Europa＇s perturbed flux tube based on the theory of thin filament. The stretched magnetic flux tube, which is motionless relative to the Europa with an angle of about 4°, was formed by the interaction of the unperturbed upstream magnetic flux tube and Europa during 720 s, and then this flux tube was accelerated by the magnetic tension. In the following 2160 s acceleration, the velocity of the magnetic flux tube was getting close to that of the background magnetic line, and the induced current was attenuating from 9×10^5A to 0. Taking the size at 1/e of initial current as the observation limit, then the Europa＇s footprint only occupied about 1 ~2 longitude, which coincides with the ultraviolet images taken with the Space Telescope imaging spectrograph. The distance of Europa＇s wake is shorter than Io＇s because the energy in perturbed flux tube is estimated about 2.3× 10^13j, only 1/10 of that of Io＇s wake. Furthermore, it was also found inthe simulation that the downstream pressure depression has ignorable influence on the motion of the magnetic flux tube.

关 键 词：木卫二 尾迹 细丝 磁通量管 数值模拟 

分 类 号：P353[天文地球—空间物理学]