3-D global hybrid simulations of magnetospheric response to foreshock processes

Feng Shi,Xueyi Wang,Yukitoshi Nishimura,Yu Lin,Boyi Wang

doi:10.1186/s40623-021-01469-2

Feng Shi, Xueyi Wang + Show 3 more

Open Access

https://doi.org/10.1186/s40623-021-01469-2

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Abstract

It has been suggested that ion foreshock waves originating in the solar wind upstream of the quasi-parallel (Q-||) shock can impact the planetary magnetosphere leading to standing shear Alfvén waves, i.e., the field line resonances (FLRs). In this paper, we carry out simulations of interaction between the solar wind and terrestrial magnetosphere under radial interplanetary magnetic field conditions by using a 3-D global hybrid model, and show the properties of self-consistently generated field line resonances through direct mode conversion in magnetospheric response to the foreshock disturbances for the first time. The simulation results show that the foreshock disturbances from the Q-|| shock can excite magnetospheric ultralow-frequency waves, among which the toroidal Alfvén waves are examined. It is found that the foreshock wave spectrum covers a wide frequency range and matches the band of FLR harmonics after excluding the Doppler shift effects. The fundamental harmonic of field line resonances dominates and has the strongest wave power, and the higher the harmonic order, the weaker the corresponding wave power. The nodes and anti-nodes of the odd and even harmonics in the equatorial plane are also presented. In addition, as the local Alfvén speed increases earthward, the corresponding frequency of each harmonic increases. The field-aligned current in the cusp region indicative of the possibly observable aurora is found to be a result of magnetopause perturbation which is caused by the foreshock disturbances, and a global view substantiating this scenario is given. Finally, it is found that when the solar wind Mach number decreases, the strength of both field line resonance and field-aligned current decreases accordingly.

Highlights

Planetary magnetic fields provide effective obstacles to the solar wind which exists ubiquitously in astrophysical environments (Chapman and Ferraro 1930)
Summary In this paper, self-consistent 3-D global hybrid simulations are carried out to investigate the Field line resonance (FLR) which are generated by the foreshock disturbance processes under radial Interplanetary magnetic field (IMF) conditions, and the simulation results support the scenario from the observations (Shen et al 2018; Wang et al 2019) that the compressional waves arising from the Q-|| foreshock region excite toroidal Alfvén waves in the magnetosphere
These results provide insights for space environment of magnetized planets, and are summarized as follows: 1. This paper presents the first global simulations of the FLRs driven by foreshock processes

Summary

Introduction

Planetary magnetic fields provide effective obstacles to the solar wind which exists ubiquitously in astrophysical environments (Chapman and Ferraro 1930). −1 i0 in the noon-meridian and equatorial planes obtained from the simulation together with typical magnetic field lines (arrows showing the field line direction), which shows the 3-D self-consistently generated dayside global system with ion foreshock, bow shock, magnetosheath, magnetopause and magnetosphere.

Results

Conclusion