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

Abstract

Although foreshock transients can generate strong magnetospheric Pc5 ultralow-frequency (ULF) waves, whether they can modulate the energy of magnetospheric ions is still poorly understood.In this study, we analyze the strong magnetospheric ion energy modulations in a foreshock transient event on October 30, 2008, based on the magnetospheric observations by the time history of events and macroscale interactions during substorms A and D in the prenoon sector. ULF wave-induced  E B drift accelerated the cold ions up to ∼10 keV and the enhanced ion fluxes have wave-like patterns. There is another portion of enhanced ion fluxes from ∼0.8 to ∼10 keV but with strong energy dispersions in this event. By comparing the observations and the theoretical prediction, we for the first time found that the drift-bounce resonances played a major role in modulating the energy of those ions with energy dispersions, during the interactions between the ions and the foreshock transient-driven Pc5 ULF wave with growing and damping effects.Plain Language Summary Foreshock transients are generated in front of the Earth's bow shock. Those transient structures are always associated with strong dynamic pressure variations, which enables them to strongly compress and inflate the Earth's magnetosphere. However, according to the past studies on foreshock transients, whether they can modulate the energy of magnetospheric ions is still poorly understood. In this study, we analyze the strong magnetospheric ion energy modulations in a foreshock transient event on October 30, 2008, based on the magnetospheric observations by the time history of events and macroscale interactions during substorms A and D in the prenoon sector. We found two mechanisms of modulating ion energies in this event. First, the ultralow frequency (ULF) wave-induced electric field accelerated the cold ions, of which the ion fluxes have wave-like patterns. However, it had a limited contribution to the enhanced ion fluxes with strong energy dispersions. Second, by comparing the observations and the theoretical prediction, we for the first time found that the driftbounce resonances played a major role in modulating the energy of those ions with energy dispersions, during the interactions between the ions and the foreshock transient-driven ULF wave with growing and damping effects. WANG ET AL.

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

“…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).…”

“…Note that there are weak perturbations in the foreshock and the magnetosheath due to the foreshock ULF waves. The TD first encounters the foreshock ions just outside the dayside bow shock at t ∼44 min and foreshock transient perturbations are formed (see Wang B. et al (2021) for more details about the initiation of the foreshock transient).…”

“…They showed the evolution of the foreshock transient perturbations as they propagate from the dayside to nightside foreshock and the associated magnetosheath perturbations in the flanks. In this paper, we use the simulation by Wang B. et al (2021) to show qualitatively the 3D structure of the flank magnetopause distortion caused by foreshock transients and the impact on the magnetosphere and ionosphere. The results presented here should provide a qualitative understanding of the impacts common to the foreshock transients of different types since they all have the same features of density perturbations (low-density core and high-density edge).…”

“…We also present two observation events to provide qualitative comparisons with the simulated magnetopause distortion and ionospheric perturbations. Wang B. et al (2021) used the AuburN Global hybrId CodE in 3D (ANGIE3D) hybrid code (Lin et al, 2014) to simulate foreshock transients resulting from the interaction of an IMF directional TD (i.e., with direction change only) with the foreshock ions. The simulation model and setup for this simulation is described in Simulation Model and Setup.…”

Interaction between long-period ULF waves and charged particle in the magnetosphere: theory and observations (overview)

“…Стандартные способы наблюдения азимутальномелкомасштабных волн включают в себя искусственные спутники Земли и радары. Первые примеры волн с m>>1, наблюдаемых с помощью этих методов, были описаны в статьях [Cummings et al, 1969;Allan et al, 1982;Walker et al, 1982]. Применяются и другие методы изучения этих волн: с помощью пульсаций риометрического поглощения [Beharrell et al, 2010;Моисеев и др., 2020], по данным о полной электронной концентрации в ионосфере, полученным с помощью приемников GPS [Watson et al, 2016;Zhai et al, 2021], по оптическим данным [Motoba et al, 2015;Baddeley et al, 2017].…”