Modeling of the heliospheric interface: multi-component nature of the heliospheric plasma

Abstract

We present a new model of the heliospheric interface -the region of the solar wind interaction with the local interstellar medium. This new model performs a multi-component treatment of charged particles in the heliosphere. All charged particles are divided into several co-moving types. The coldest type, with parameters typical of original solar wind protons, is considered in the framework of fluid approximation. The hot pickup proton components created from interstellar H atoms and heliospheric ENAs by charge exchange, electron impact ionization and photoionization are treated kinetically. The charged components are considered self-consistently with interstellar H atoms, which are described kinetically as well. To solve the kinetic equation for H atoms we use the Monte Carlo method with splitting of trajectories, which allows us 1) to reduce statistical uncertainties allowing correct interpretation of observational data; 2) to separate all H atoms in the heliosphere into several populations depending on the place of their birth and on the type of parent protons.

Galactic cosmic rays measured by UVS on Voyager 1 and the end of the modulation

“…Very recently, Gurnett et al (2013) have detected plasma oscillations whose frequency implies a density of 0.06−0.08 cm −3 , which is far above the solar wind heliosheath range, and, instead, very close to the expected circumsolar ISM value that is deduced from the neutral hydrogen deceleration at the entrance in the heliosphere (0.04−0.07 cm −3 , Izmodenov et al 1999). It is not clear yet whether the steep density ramp inferred by Gurnett et al (2013) between October 2012 and April 2013 corresponds to the heliopause discontinuity itself or the wider and more distant density enhancement in the pile-up region (e.g., Malama et al 2006;Zank et al 2013). In any case, such data is a confirmation of the entry into the ISM, contrary to most predictions of a larger distance to the heliopause.…”

Low Energy Neutral Atoms From the Heliosheath

“…The pickup ion distribution created in the upstream solar wind (process 3a in Figure 1) is also decelerated and heated across the termination shock. Some of these pickup ions charge exchange in the inner heliosheath, creating a population of ENAs with energy that is higher than energies of populations created in processes 1 and 2 in Figure 1 (Malama et al 2006). Finally, the highest energy ENAs (process 4 in Figure 1) are produced by solar wind (and pickup ions) that are accelerated at the termination shock and by turbulence in the inner heliosheath before charge exchanging in the inner heliosheath (Chalov & Fahr 2000;Chalov et al 2003;Fahr et al 2011;Siewert et al 2012;Kucharek et al 2013).…”

“…The resulting ENAs (Gruntman et al 2001) may contribute to the lowest energy population observable by IBEX. Some fraction of the pickup ion distribution created by charge exchange in the inner heliosheath may undergo a second charge exchange (process 2 in Figure 1), also creating a low energy ENA population (Malama et al 2006). The pickup ion distribution created in the upstream solar wind (process 3a in Figure 1) is also decelerated and heated across the termination shock.…”

The Galactic Environment of the Sun: Interstellar Material Inside and Outside of the Heliosphere

“…These models should ideally use a sophisticated multicomponent treatment of the plasma in the heliosphere instead of the usual simple single-fluid treatment, as multicomponent models have been found to result in significantly different heliosheath neutral populations, and better reproduction of heliosheath absorption (Malama et al 2006;Wood et al 2007). In any case, once IBEX data are available it will be very interesting to see if models are capable of simultaneously reproducing both the local ENA spectra seen by IBEX and the Lyα absorption data.…”