Affiliation of Author(s):航天学院
Journal:ADVANCES IN SPACE RESEARCH
Key Words:Gyrophase bunching Oxygen band waves Wave-particle interaction
Abstract:Gyrophase bunched ions were first detected in the upstream region of the Earth's bow shock in the early 1980s which is formed by the microphysical process associated with reflected solar wind ions at the bow shock. Inside the magnetosphere, the results of computer simulations demonstrated that nonlinear wave-particle interaction can also result in the gyrophase bunching of particles. However, to date direct observations barely exist regarding this issue occurred inside the magnetosphere. In this paper, we report for the first time an event of gyrophase bunched ions observed in the near-Earth plasma sheet. The nongyrotropic distributions of ions were closely accompanied with the electromagnetic waves at the oxygen cyclotron frequency. The phase of bunched ions and the phase of waves mainly have very narrow phase differences (<30 degrees) when the O+ band waves are remarkably enhanced, which indicates that the wave and particle are closely corotating. The "electric phase bunching" is considered to be a possible mechanism for the formation of the gyrophase bunched distributions in this case. The MVA analysis suggests that the oxygen band waves possess left helicity with respect to the propagation direction, which agrees with the characteristic of electromagnetic ion cyclotron waves. The observation of O+ ions composition suggests that the oxygen band waves are excited due to the enhancements of the O+ ion density. This study suggests that the gyrophase bunching is a significant nonlinear effect that exists not only in the bow shock but also in the inner magnetosphere. (C) 2016 COSPAR. Published by Elsevier Ltd. All rights reserved.
ISSN No.:0273-1177
Translation or Not:no
Date of Publication:2017-01-01
Co-author:Zhai, Hao,Gao, Zhuxiu,hcy
Correspondence Author:王志强
Date of Publication:2017-01-01