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Omidi N.,Solana Scientific Inc. Solana Beach | Berchem J.,University of California at Los Angeles | Sibeck D.,NASA | Zhang H.,University of Alaska Fairbanks
Journal of Geophysical Research A: Space Physics | Year: 2016

Spacecraft observations and global hybrid (kinetic ions and fluid electrons) simulations have demonstrated that ion dissipation processes at the quasi-parallel bow shock are associated with the formation of structures called spontaneous hot flow anomalies (SHFAs). Previous simulations and recent spacecraft observations have also established that SHFAs result in the formation of magnetosheath filamentary structures (MFS). In this paper we demonstrate that in addition to MFS, SHFAs also result in the formation of magnetosheath cavities that are associated with decreases in density, velocity, and magnetic field and enhancements in temperature. We use the results of a global MHD run to determine the change in the magnetosheath properties associated with cavities due to ion kinetic effects. The results also show the formation of regions of high flow speed called magnetosheath jets whose properties as a function of solar wind Mach number are described in this study. Comparing the properties of the simulated magnetosheath cavities and jets to past spacecraft observations provides good agreement in both cases. We also demonstrate that pressure variations associated with cavities and SHFAs in the sheath result in a continuous sunward and antisunward magnetopause motion. This result is consistent with previous suggestions that SHFAs may be responsible for the generation of ion cyclotron waves and precipitation of ring current protons in the outer magnetosphere. ©2016. American Geophysical Union. Source


Omidi N.,Solana Scientific Inc. Solana Beach | Russell C.T.,University of California at Los Angeles | Jian L.K.,University of Maryland College Park | Isenberg P.,University of New Hampshire | Wei H.Y.,University of California at Los Angeles
Journal of Geophysical Research A: Space Physics | Year: 2014

With the objective to understand the generation, propagation, and nonlinear evolution of ion cyclotron waves (ICWs) in the corona and solar wind, we use electromagnetic hybrid (kinetic ions and fluid electrons) simulations with a nonuniform magnetic field. ICWs are generated by the temperature anisotropy of O5+ ions as minority species in a proton-electron plasma with uniform density. A number of magnetic field models are used including radial and spiral with field strength decreasing linearly or with the square of the radial distance. O5+ ions with perpendicular temperature larger than parallel are initially placed in the high-magnetic field regions. These ions are found to expand outward along the magnetic field. Associated with this expansion, ion cyclotron waves propagating along the magnetic field are also seen to expand outward. These waves are generated at frequencies below the local gyrofrequency of O5+ ions propagating parallel and antiparallel to the magnetic field. Through analysis of the simulation results we demonstrate that wave generation and absorption take place at all radial distances. Comparing the simulation results to observations of ICWs in the solar wind shows some of the observed wave characteristics may be explained by the mechanism discussed in this paper. © 2014. American Geophysical Union. All Rights Reserved. Source

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