Short large‐amplitude magnetic structures and whistler wave precursors in a full‐particle quasi‐parallel shock simulation

Abstract

[1] A one-dimensional (1-D) full-particle electromagnetic simulation code (PIC) is used to investigate the role of upstream whistler and low-frequency upstream waves during cyclic reformation of a medium Alfvén Mach number quasi-parallel collisionless shock (magnetic field -shock normal angle = 30°). The ion to electron mass ratio is assumed to be 100. Compared with previous PIC simulations, the upstream region is large enough to allow for the emergence of low-frequency upstream waves by the interaction of backstreaming ions with the solar wind via an ion/ion beam instability in the far upstream region. It is shown that the low-frequency upstream waves steepen up into pulsations (or short large-amplitude magnetic structures (SLAMS)), as has been shown earlier by hybrid simulations. As these pulsations are added to the shock and thus comprise the shock, the upstream edge radiates a phase standing whistler train. This whistler train propagates partway into the newly arriving pulsation. The nonlinear interaction of reflected ions and incoming solar wind ions in the electrostatic potential of the whistler leads to ion trapping and rapid whistler damping. This results in SLAMS consisting of two regions with different ion temperatures. The cyclic reformation is essentially due to the SLAMS being added to the shock and is of larger scale ($10 ion inertial lengths) as compared with the whistler scale.INDEX TERMS: 2154 Interplanetary Physics: Planetary bow shocks; 7851 Space Plasma Physics: Shock waves; 7843 Space Plasma Physics: Numerical simulation studies; 7867 Space Plasma Physics: Wave/particle interactions; KEYWORDS: collisionless shocks, bow shock, reformation, short large-amplitude magnetic structures, whistler waves, particle-in-cell simulation Citation: Scholer, M., H. Kucharek, and I. Shinohara, Short large-amplitude magnetic structures and whistler wave precursors in a full-particle quasi-parallel shock simulation,

Statistical study of foreshock cavitons

“…It is well known that deep inside the quasi-parallel foreshock, two structures arise from ULF fluctuations: the shocklets and the short-large amplitude magnetic structures (SLAMS) Greenstadt et al, 1995;Scholer et al, 2003;Schwartz and Burgess, 1991;Schwartz, 1991;Schwartz et al, 1992;Giacalone et al, 1993). In the magnetic field data, the shocklets exhibit a compressive character with one steepened, shock-like edge, often accompanied by a whistler wave precursor.…”

Quantified energy dissipation rates in the terrestrial bow shock: 1. Analysis techniques and methodology

“…The total relative density of the reflected particles ranged from ∼20 to 40%, while the beam-like ions only composed ∼ 1-5%. While these relative densities are high, there are a few important things to take note of: a. intermediate/diffuse ions are thought to be the free energy source for shocklets and short large-amplitude magnetic structures [e.g., Scholer et al, 2003;Tsubouchi and Lembège, 2004], which can locally produce j o due to the associated gradients in B o ; b. the relative drift between reflected ions and incident electrons (e.g., a current) can provide the free energy for an instability responsible for one of the high-frequency waves of interest (discussed in Paper II) [e.g., Matsukiyo and Scholer, 2006;Muschietti and Lembège, 2013]; c. reflected ions, if transmitted into the downstream as a gyrating ring, could excite Alfvén ion cyclotron waves [e.g., Davidson and Ogden, 1975] and other electromagnetic waves [e.g., Lu and Wang, 2006;Hao et al, 2014]; d. if the reflected ions generate low-frequency waves, then they contribute to our dissipation estimates through j o ; e. if the reflected ions generate high-frequency waves, then they contribute to our dissipation estimates through both j o and E. 3. Thus, our estimates of ( −j o ⋅ E ) are still relevant because they can include effects from particle reflection directly or indirectly.…”

“…Thus, the ramp currents [e.g., Sagdeev, 1966;Gary, 1981], voids in electron velocity distributions [e.g., Hull et al, 1998Hull et al, , 2000Hull et al, , 2001Mitchell and Schwartz, 2014], and reflected ion currents [e.g., Scholer et al, 2003;Tsubouchi and Lembège, 2004;Matsukiyo and Scholer, 2006;Muschietti and Lembège, 2013] are all capable of producing instabilities that radiate electromagnetic waves.…”

Quantified energy dissipation rates in the terrestrial bow shock: 2. Waves and dissipation

“…Multiple magnetic fluctuations in and around collisionless shock waves have been shown to be consistent with magnetosonic-whistler waves, and these fluctuations are predicted to have multiple sources including but not limited to dispersive radiation [e.g., Tidman and Northrop, 1968;Kennel et al, 1985;Krasnoselskikh et al, 2002], diffuse ions [e.g., Scholer et al, 2003;Tsubouchi and Lembège, 2004], reflected gyrating ion beams [e.g., Wu et al, 1983;Riquelme and Spitkovsky, 2011;Comişel et al, 2011], field-aligned ion beams [e.g., Akimoto et al, 1993], and streaming and anisotropic electron velocity distributions [e.g., Sentman et al, 1983]. Theory [e.g., Wu et al, 1983;Cairns and McMillan, 2005] predicts that they can stochastically accelerate electrons parallel to B o and heat ions perpendicular to B o when propagating at highly oblique angles, which has been supported by observations [e.g., Wilson et al, 2012].…”

“…The large variability observed in |B o | and B o could be explained by the following: sudden expansions and contractions of the bow shock due to changing solar wind conditions [e.g., Horbury et al, 2001]; nonstationary shock reformation due to nonlinear waves [e.g., Krasnoselskikh et al, 2002;Hellinger et al, 2007;Lobzin et al, 2007]; nonstationary shock reformation due to accumulation of reflected particles [e.g., Lembège and Savoini, 2002;Lembège et al, 2009;Yang et al, 2009;Su et al, 2012]; or compressive nonlinear magnetic pulsations driven by the free energy from reflected ions [e.g., Scholer et al, 2003;Tsubouchi and Lembège, 2004]. Regardless of their source, the large fluctuations in B o are in phase with changes in N i and correlated with significant deflections in V bulk and increases in T e and T i .…”