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/V sw ∼1. 3 - 2. 4, T∥,b/Tb ∼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. 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 ©2012. American Geophysical Union. All Rights Reserved.