Upstream proton cyclotron waves: occurrence and amplitude dependence on IMF cone angle at Mars——from MAVEN observations  

作　　者：Di Liu ZhongHua Yao Yong Wei ZhaoJin Rong LiCan Shan Stiepen Arnaud Espley Jared HanYing Wei WeiXing Wan 

机构地区：[1]Key Laboratory of Earth and Planetary Physics,Institute of Geology and Geophysics,Chinese Academy of Sciences,Beijing 100029,China [2]College of Earth and Planetary Sciences,University of Chinese Academy of Sciences,Beijing 100049,China [3]Laboratoire de Physique Atmospherique et Planetaire,STAR institute,Universite de Liege,Liege,Belgium [4]NASA Goddard Space Flight Center,Greenbelt,Maryland,USA [5]Department of Earth,Planetary and Space Sciences,University of California,Los Angeles,California,USA

出　　处：《Earth and Planetary Physics》2020年第1期51-61,共11页地球与行星物理（英文版）

基　　金：supported by the Strategic Priority Research Program of Chinese Academy of Sciences (Grant No.XDA17010201);supported by Thousand Young Talents Program of China and Chinese NSFC grant (41525016, 41474155, 41661164034, 41621004, 41374180, 41774188);cofunded by EU. A;supported by the Fund for Scientific Research (F.R.S.FNRS)

摘　　要：Proton cyclotron waves(PCWs)can be generated by ion pickup of Martian exospheric particles in the solar wind.The solar wind ion pickup process is highly dependent on the“IMF cone angle”—the angle between the solar wind velocity and the interplanetary magnetic field(IMF),which also plays an important role in the generation of PCWs.Using data from 2.15 Martian years of magnetic field measurements collected by the Mars Atmosphere and Volatile Evolution(MAVEN)mission,we have identified 3307 upstream PCW events.Their event number distribution decreases exponentially with their duration.A statistical investigation of the effects of IMF cone angle on the amplitudes and occurrence rates of PCWs reveals a slight tendency of PCWs’amplitudes to decrease with increasing IMF cone angle.The relationship between the amplitude and IMF cone angle is weak,with a correlation coefficient r=–0.3.We also investigated the influence of IMF cone angle on the occurrence rate of PCWs and found that their occurrence rate is particularly high for intermediate IMF cone angles(~18°–42°)even though highly oblique IMF orientation occurs most frequently in the upstream region of the Martian bow shock.We also conclude that these variabilities are not artefacts of temporal coverage biases in MAVEN sampling.Our results demonstrate that whereas IMF cone angle strongly influences the occurrence of PCWs,IMF cone angle may also weakly modulate their amplitudes in the upstream region of Mars.Proton cyclotron waves(PCWs) can be generated by ion pickup of Martian exospheric particles in the solar wind. The solar wind ion pickup process is highly dependent on the "IMF cone angle" — the angle between the solar wind velocity and the interplanetary magnetic field(IMF), which also plays an important role in the generation of PCWs. Using data from 2.15 Martian years of magnetic field measurements collected by the Mars Atmosphere and Volatile Evolution(MAVEN) mission, we have identified 3307 upstream PCW events. Their event number distribution decreases exponentially with their duration. A statistical investigation of the effects of IMF cone angle on the amplitudes and occurrence rates of PCWs reveals a slight tendency of PCWs’ amplitudes to decrease with increasing IMF cone angle. The relationship between the amplitude and IMF cone angle is weak, with a correlation coefficient r = –0.3.We also investigated the influence of IMF cone angle on the occurrence rate of PCWs and found that their occurrence rate is particularly high for intermediate IMF cone angles(～18°–42°) even though highly oblique IMF orientation occurs most frequently in the upstream region of the Martian bow shock. We also conclude that these variabilities are not artefacts of temporal coverage biases in MAVEN sampling. Our results demonstrate that whereas IMF cone angle strongly influences the occurrence of PCWs, IMF cone angle may also weakly modulate their amplitudes in the upstream region of Mars.

关 键 词：ion pickup proton cyclotron waves Martian exosphere 

分 类 号：P185.3[天文地球—天文学]