Dynamical evolution of the termination Shock: consequences for charged particle acceleration

During the 2002-2004 precursor events and in the heliosheath, Voyager 1 observed several distinct energetic particle populations with different power law spectra, as well as a high-energy modulated component. We investigate the possibility that some of these populations could be produced by diffusive shock acceleration at a termination shock (TS) that is subjected to collisions with large scale structures, such as merged interaction regions (MIR). Using a simple 1D model where an MIR is initiated as a velocity enhancement followed by a rarefaction, we show that the TS compression ratio first decreases at the onset of the interaction followed by an increase during the passage of a rarefaction. We demonstrate that particles accelerated at such a dynamic shock would possess a multiple component spectrum that bears a qualitative resemblance to Voyager 1 observations. Our results also predict inward TS motion during the later stages of the interaction, consistent with the period of anomalously low radial velocity in the heliosheath in early 2005.