Shocklets, SLAMS, and field-aligned ion beams in the terrestrial foreshock

摘要

We present Wind spacecraft observations of ion distributions showing field-aligned beams (FABs) and large-amplitude magnetic fluctuations composed of a series of shocklets and short large-amplitude magnetic structures (SLAMS). The FABs are found to have T_b ～80 - 850 eV, V_b/V _(sw) ～1. 3 - 2. 4, T_(//),_b/T_b ～1-8, and n_b_o ～0.2-11%. Saturation amplitudes for ion/ion resonant and non-resonant instabilities are too small to explain the observed SLAMS amplitudes. We show two examples where groups of SLAMS can act like a local quasi-perpendicular shock reflecting ions to produce the FABs, a scenario distinct from the more common production at the quasi-perpendicular bow shock. The SLAMS exhibit a foot-like magnetic enhancement with a leading magnetosonic whistler train, consistent with previous observations. Strong ion and electron heating are observed within the series of shocklets and SLAMS with temperatures increasing by factors a‰ 5 and a‰ 3, respectively. Both the core and halo electron components show strong perpendicular heating inside the feature. Key Points Field-aligned ion beams produced locally by SLAMS SLAMS cause strong anisotropic ion and electron heating SLAMS can act like local quasi-perpendicular shocks