火星感应磁层边界不稳定性研究:K-H波及其产生的磁通量绳  

Study on the instability in Mars'induced magnetospheric boundary:Kelvin-Helmholtz waves and associated magnetic flux ropes

作　　者：吴放 葛亚松[1,2,3] 黄灿 王磊 杜爱民[1,2,3] WU Fang;GE YaSong;HUANG Can;WANG Lei;DU AiMin(CAS Engineering Laboratory for Deep Resources Equipment and Technology,Institute of Geology and Geophysics,Chinese Academy of Sciences,Beijing 100029,China;Innovation Academy for Earth Science,Chinese Academy of Sciences,Beijing 100029,China;College of Earth and Planetary Sciences,University of Chinese Academy of Sciences,Beijing 100049,China)

机构地区：[1]中国科学院地质与地球物理研究所,中国科学院深地资源装备技术工程实验室,北京100029 [2]中国科学院地球科学研究院,北京100029 [3]中国科学院大学地球与行星科学学院,北京100049

出　　处：《地球物理学报》2024年第9期3301-3310,共10页Chinese Journal of Geophysics

基　　金：国家自然科学基金(42330207,42274222,42188101,42025404,41974186,42174188,41674163);中国科学院先导B计划(XDB41000000);民用航天预研项目(D020303,D020308,D020103,D020104)资助。

摘　　要：火星感应磁层边界的等离子体不稳定性,如边界层处速度剪切激发的Kelvin-Helmholtz(K-H)不稳定性,对火星感应磁层结构和磁层离子输运过程具有重要的影响.本文利用Mars Atmosphere and Volatile EvolutioN(MAVEN)卫星搭载的Magnetometer(MAG)和Super Thermal and Thermal Ion Composition(STATIC)仪器所提供的磁场和等离子数据,分析了2018年5月21日火星感应磁层边界处观测到的K-H不稳定性事件,发现在磁场、重离子通量、离子成分与密度、和离子速度上存在五个连续的准周期变化,估算K-H波的周期为~100 s,同时在其中两个K-H涡旋内发现了磁通量绳结构.磁通量绳的轴向方向与边界层法向准垂直,且其中的离子成分与涡旋内电离层等离子体成分接近,表明此处的磁通量绳有可能是在K-H波的发展过程中形成.磁通量绳的整体速度也远大于此处的离子逃逸速度,这可能导致重离子O^(+)和O_(2)^(+)从火星大气中快速逃逸.The plasma instabilities in Mars'induced magnetospheric boundary such as the Kelvin-Helmholtz(K-H)instability induced by velocity shear,significantly affect the structure of Mars'induced magnetosphere and the transport of ions within the Martian magnetosphere.In this study,using the magnetic field and plasma data provided by the Magnetometer(MAG)and Super Thermal and Thermal Ion Composition(STATIC)instruments onboard the Mars Atmosphere and Volatile EvolutioN(MAVEN)spacecraft,we analyze the K-H instability events observed at the induced magnetospheric boundary on May 21,2018.We identify five consecutive quasi-periodic variations in the magnetic field,heavy ion flux,ion composition and density,and ion velocity.The estimated period of the K-H waves is approximately 100 seconds.Furthermore,we observe magnetic flux rope structures within two of the K-H vortices.The axial direction of the magnetic flux rope is nearly perpendicular to the normal of the boundary layer,and its ion composition is similar to that of the ionospheric plasma within the vortices.This indicates that the magnetic flux rope in this region is likely formed during the development of Kelvin-Helmholtz waves.The overall velocity of the magnetic flux rope is much greater than the ion escape velocity in this region,which could result in the rapid escape of heavy ions O^(+)and O_(2)^(+)from the Martian atmosphere.

关 键 词：K-H不稳定性 磁通量绳 大气逃逸 

分 类 号：P353[天文地球—空间物理学]