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

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 similar to 80 - 850 eV, V-b/V-sw similar to 1.3 - 2.4, T-perpendicular to,T-b/T-parallel to,T-b similar to 1-8, and n(b)/n(o) similar to 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 greater than or similar to 5 and greater than or similar to 3, respectively. Both the core and halo electron components show strong perpendicular heating inside the feature.