火星磁鞘中小尺度磁洞发生率的观测  

Observations of occurrence rates of small-scale magnetic holes in the Martian magnetosheath

作　　者：陈洋军 吴明雨 肖苏东 王国强 陈远强 娄悦群 杜爱民[4] 张铁龙 CHEN YangJun;WU MingYu;XIAO SuDong;WANG GuoQiang;CHEN YuanQiang;LOU YueQun;DU AiMin;ZHANG TieLong(Institute of Space Science and Applied Technology,Harbin Institute of Technology,Shenzhen 518055,China;Space Research Institute,Austrian Academy of Sciences,Graz A-8042,Austria;Chinese Academy of Sciences Center for Excellence in Comparative Planetology,Hefei 230026,China;Institute of Geology and Geophysics,Chinese Academy of Sciences,Beijing 100029,China)

机构地区：[1]哈尔滨工业大学(深圳)空间科学与应用技术研究院,深圳518055 [2]奥地利科学院空间研究所,格拉茨A-8042 [3]中国科学院比较行星学卓越创新中心,合肥230026 [4]中国科学院地质与地球物理研究所,北京100029

出　　处：《地球物理学报》2023年第3期871-880,共10页Chinese Journal of Geophysics

基　　金：国家自然科学基金项目(41774167,41774171,41974205,41804157,41904156和42130204);中国澳门基金会和国防科工局民用航天技术预先研究项目(D020103)资助。

摘　　要：小尺度磁洞是一种尺度通常小于质子回旋半径的磁结构,其特征是该结构内的磁场强度相对于周围环境存在一个显著的减弱.这种结构可能与能量转换和粒子加速、磁场重联和动力学尺度上的湍流密切相关.最近,小尺度磁洞在金星和火星磁鞘中被报道.利用美国航天局MAVEN(Mars Atmosphere and Volatile EvolutioN)卫星4个月的观测数据,本文统计分析了火星磁鞘中的小尺度磁洞的发生率.统计结果表明,小尺度磁洞主要出现在环境磁场强度在4≤B≤12 nT,等离子体的速度在250~450 km·s^(-1),密度在3≤N≤12 cm^(-3)范围.在这个参数范围内,小尺度磁洞在背景太阳风流速相对更快、背景磁场相对更弱的时候发生率更高,且相对集中在背景密度在6~9 cm^(-3)之间.此外,靠近火星磁鞘中心的小尺度磁洞的发生率要高于磁鞘两侧,这意味着火星磁鞘可能是小尺度磁洞的一个源区.Small-scale magnetic holes are usually sub-proton magnetic structures characterized by a significant decrease of magnetic field magnitude, and then restoring to the original background magnetic field strength. These structures are found to be closely related to energy conversion and particle acceleration, magnetic reconnection, and turbulence at the kinetic scale. Recently, these magnetic holes are reported in Venusian and Martian magnetosheath. With 4-months data of MAVEN(Mars Atmosphere and Volatile EvolutioN), the occurrence rates of small-scale magnetic holes in the Martian magnetosheath are investigated in this work. Our results show that small-scale magnetic holes are mainly detected in the plasma with the ambient magnetic field magnitude 4≤B≤12 nT, plasma bulk velocity range from 250 km·s^(-1)to 450 km·s^(-1), and plasma density 3≤N≤12cm^(-3). In such environment, small-scale magnetic holes have a relatively higher occurrence rate when the background solar wind velocity is relatively faster and the background magnetic field is relatively weaker, and they are relatively concentrated in the background density between 6~9 cm^(-3). This parameter range may be related to the formation mechanism of small-scale magnetic holes. In addition, the occurrence rates of the small-scale magnetic holes near the center magnetosheath are higher than those in the flanks. These results indicate that the Martian magnetosheath is a potential source of small-scale magnetic holes.

关 键 词：火星 磁鞘 小尺度磁洞 发生率 

分 类 号：P353[天文地球—空间物理学]