Global Propagation of Magnetospheric Pc5 ULF Waves Driven by Foreshock Transients

Abstract

Pc5 (2-7 mHz) ultralow frequency (ULF) waves play a significant role in resonating with particles and transferring energy in the coupled magnetospheric and ionospheric system. Recent studies found that Pc5 ULF waves can be triggered by foreshock transients which can perturb the magnetopause through dynamic pressure variation. However, whether foreshock transient-driven Pc5 ULF waves are geoeffective and can propagate globally is still poorly understood. In this study, we take advantage of the conjunction between in situ (by the THEMIS probes, Geotail satellite, GOES satellites, and Van Allen probes) and ground-based (by the all-sky imager at South Pole and ground-based magnetometers) observations to simultaneously analyze the waves from the foreshock region to the dayside and nightside magnetosphere. Both of our two events show that the Pc5 ULF waves are generated by foreshock transients in the dayside magnetosphere. The in situ observations by THEMIS A and D and the 2-D auroral signatures show that the compressional mode waves are likely broadband and coupled to the FLRs with different frequencies and different azimuthal phase speeds. This is the first report that foreshock transients can drive both low-and high-m FLRs, with the azimuthal wave numbers varying from~5 to~23. Moreover, the Pc5 ULF waves propagated antisunward to midnight, this can potentially modulate magnetospheric and ionospheric dynamics globally.

Impact of Foreshock Transients on the Flank Magnetopause and Magnetosphere and the Ionosphere

“…Compared to the enhancements when the magnetopause is distorting outward around t ∼60 min, the perturbations generated by the inward magnetopause distortion around t 61.3 min are stronger and deeper into the magnetosphere. This shows that the magnetopause distortion driven by foreshock transients can launch compressional waves within the magnetosphere, which qualitatively explains the observed enhancements in magnetospheric ULF waves associated with foreshock transients (e.g., Hartinger et al, 2013;Wang et al, 2017;Wang et al, 2018b;Wang et al, 2019;Wang B. et al, 2020).…”

“…The resulting magnetosheath perturbations and the impact on the dayside magnetopause have been simulated (e.g., Lin and Wang, 2005;Omidi et al, 2016;Sibeck et al, 2021)) and observed (e.g., Archer et al, 2014;Jacobsen et al, 2009;Kajdičet al, 2021;Sibeck et al, 1999;2000). Similar to the impact of the solar wind dynamic pressure perturbations, the magnetopause distortion driven by foreshock transients can subsequently generate ultralow frequency (ULF) waves inside the magnetosphere (e.g., Hartinger et al, 2013;Wang et al, 2017;Wang et al, 2018b;Wang et al, 2019;Wang B. et al, 2020;Shi et al, 2021;Wang B. et al, 2021), enhance particle precipitation and the resulting aurora brightness (e.g., Fillingim et al, 2011;Wang et al, 2018a;Wang et al, 2018b;Wang et al, 2019), and enhance field-aligned currents (FACs) and the associated perturbations in ionospheric currents and ground magnetic field (e.g., Kataoka et al, 2002;Murr and Hughes, 2003;Fillingim et al, 2011;Shen et al, 2018).…”

Energy Modulations of Magnetospheric Ions Induced by Foreshock Transient‐Driven Ultralow‐Frequency Waves

“…Wang, Liu et al. (2020) has shown that there were significant oscillations started at ∼08:59:00 UT in the magnetic field (Figures 1a–1c and 1i–1k), electric field (Figures 1e, 1f, 1m, and 1n), and density (Figures 1g and 1o) observed by THEMIS A and D, respectively. During 09:03:45–09:04:35, both THEMIS A and D observed magnetosheath particles with density increasing to ∼9.5 cm −3 , which indicates a transient but significant compression with an inward motion of the magnetopause.…”

“…THEMIS A and D are close to the magnetopause in the magnetosphere, according to the strong magnetic field (∼55 nT; Figures 1a-1c and 1i-1k), low plasma density (∼0.6 cm −3 ; Figures 1g and 1o) and high energy ions (several tens keV; supporting information S1). Wang, Liu et al (2020) has shown that there were significant oscillations started at ∼08:59:00 UT in the magnetic field (Figures 1a-1c and 1i-1k), electric field (Figures 1e,1f,1m,and 1n), and density (Figures 1g and 1o) observed by THEMIS A and D, respectively. During 09:03:45-09:04:35, both THEMIS A and D observed magnetosheath particles (a-c) show the observation of (a) field-aligned, (b) azimuthal and (c) radial components of the magnetic field in field-aligned coordinate, respectively, observed by the time history of events and macroscale interactions during substorms (THEMIS) A.…”

Statistical Study of Foreshock Transients in the Midtail Foreshock

“…As a result, when they encounter the bow shock, the local bow shock will move outward. Such perturbations can propagate into the magnetosheath and disturb the magnetopause and thus magnetosphere‐ionosphere system (e.g., Archer et al., 2014, 2015; Shen et al., 2018; Sibeck, Borodkova, et al., 1999; Turner, Eriksson, et al., 2011; B. Wang et al., 2018, 2020; Zhao et al., 2017a).…”