Open AccessUpstream proton cyclotron waves: occurrence and amplitude dependence on IMF cone angle at Mars — from MAVEN observations
Author(s) -
Liu Di,
Yao ZhongHua,
Wei Yong,
Rong ZhaoJin,
Shan LiCan,
Arnaud Stiepen,
Jared Espley,
Wei HanYing,
Wan WeiXing
Publication year - 2020
Publication title -
earth and planetary physics
Language(s) - English
Resource type - Journals
ISSN - 2096-3955
DOI - 10.26464/epp2020002
Subject(s) - solar wind , martian , physics , atmosphere of mars , interplanetary magnetic field , magnetosheath , amplitude , mars exploration program , ligand cone angle , bow shock (aerodynamics) , magnetopause , geophysics , magnetic field , shock wave , astronomy , geometry , optics , mechanics , mathematics , quantum mechanics , conical surface
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.