火星电离层电子浓度昼夜变化特性研究

An investigation on the variations of dayside and nightside electron densities of the Martian ionosphere

本文利用MAVEN卫星Langmuir Probe and Waves(LPW)仪器的在轨电子浓度探测数据,研究了火星电离层电子浓度随太阳天顶角(Solar Zenith Angle,SZA)的变化以及昼夜电子浓度变化的异同.基于2014年至2017年期间MAVEN的电子浓度数据,我们发现:在200km以下,白天电离层电子浓度主要受光化学平衡控制,由于白天光电离过程使得昼夜电子浓度差异较大,此时电离层昼夜传输能影响到的最大范围约在SZA=110°;而在200km以上,白天电离层受输运过程控制,此时昼夜电子浓度差别较小,电离层昼夜间电子浓度变化较为缓慢.通过研究MAVEN在deep-dip(低高度深入探测)期间的电子浓度数据,我们发现火星磁场会显著影响夜间200km以下的电子浓度分布结构,强磁场中闭合磁力线对电子沉降过程的阻碍作用使得在夜间该区域的电子浓度小于相邻区域.同时,通过比较deep-dip期间昼夜电子浓度随高度的变化,发现夜间电子沉降作用的影响可能主要集中在160km以下.

In this study,electron density data from Langmuir Probe and Waves（LPW）instrument onboard MAVEN are used to investigate the variations of the Martian ionosphere with Solar Zenith Angle（SZA）and the day-night difference of electron density.By analyzing electron density data during 2014—2017,we found that,the photochemical process is more important than the transport process below 200 km,and the day-night plasma transport can affect the electron density at SZA〈110°.For the region above 200 km,the transport process can greatly affect the structure of the topside ionosphere,and the day-night difference of electron densities is much smaller than that below 200 km,and electron density decreases gradually with increasing SZA.In addition,we analyzed the electron density data during MAVEN′s deep-dip campaigns.It was found that the strong geomagnetic fields in the southern hemisphere could affect the electron density at night.The closed geomagnetic lines might obstruct the electron precipitating process and causeadecrease in electron density as compared with surrounding regions.By comparing the electron density profiles during the deep-dip campaigns,it was found that the precipitation electrons probably affect the electron density below 160 km at night.