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

Abstract

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 Tb ~ 80 − 850 eV, Vb/Vsw ~ 1. 3 − 2. 4, T⊥,b/T∥,b ~ 1–8, and nb/no ~ 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 ≳ 5 and ≳ 3, respectively. Both the core and halo electron components show strong perpendicular heating inside the feature.