Three-dimensional Features of the Outer Heliosphere Due to Coupling between the Interstellar and Heliospheric Magnetic Field. V. The Bow Wave, Heliospheric Boundary Layer, Instabilities, and Magnetic Reconnection

Abstract

The heliosphere is formed due to interaction between the solar wind (SW) and local interstellar medium (LISM). The shape and position of the heliospheric boundary, the heliopause, in space depend on the parameters of interacting plasma flows. The interplay between the asymmetrizing effect of the interstellar magnetic field and charge exchange between ions and neutral atoms plays an important role in the SW-LISM interaction. By performing three-dimensional, MHD plasma / kinetic neutral atom simulations, we determine the width of the outer heliosheath -the LISM plasma region affected by the presence of the heliosphere -and analyze quantitatively the distributions in front of the heliopause.It is shown that charge exchange modifies the LISM plasma to such extent that the contribution of a shock transition to the total variation of plasma parameters becomes small even if the LISM velocity exceeds the fast magnetosonic speed in the unperturbed medium. By performing adaptive mesh refinement simulations, we show that a distinct boundary layer of decreased plasma density and enhanced magnetic field should be observed on the interstellar side of the heliopause. We show that this behavior is in agreement with the plasma oscillations of increasing frequency observed by the plasma wave instrument onboard Voyager 1. We also demonstrate that Voyager observations in the inner heliosheath between the heliospheric termination shock and the heliopause are consistent with dissipation of the heliospheric magnetic field. The choice of LISM parameters in this analysis is based on the simulations that fit observations of energetic neutral atoms performed by IBEX.

Magnetic Turbulence Spectra and Intermittency in the Heliosheath and in the Local Interstellar Medium

“…The magnetic field behavior beyond the HP is determined by the interstellar magnetic field (ISMF) draping over the HP as a tangential discontinuity that separates the solar wind (SW) from the LISM. The simulations of Pogorelov et al (2009aPogorelov et al ( , 2017b; Borovikov & Pogorelov (2014) predicted the magnetic field behavior very similar to observations. The recent simulation of Kim et al (2017) shows that the ISMF "undraping" is consistent with the time-dependent processes occurring in the SW.…”

“…It was crossed in about 1 month, which gives width of about 0.3 AU. There are strong indications that this "structure" is due to the HP instability (Borovikov & Pogorelov 2014) or magnetic reconnection (Schwadron & McComas 2013;Pogorelov et al 2017b), or both.…”

MHD-shock structures of astrospheres: λ Cephei -like astrospheres

“…Webb et al (1986) already showed the importance of Mach numbers for cosmic ray acceleration in MHD models and Scherer et al (2015b) used for simplicity the parameters derived from the heliosphere. In this study, we, for the first time, have shown the Mach numbers to determine the shock structure or even its existence: If the fast magnetosonic Mach number of the ISM is lower than one, no bow shock will exist as discussed for the heliosphere (Pogorelov et al 2017b). The Mach numbers also are used to determine the MHD shock type, especially for the existence of a fast or possible slow shock.…”

“…A detailed analysis of the KH in the case of the heliosphere is given by Ruderman & Brevdo (2006), where the authors show that the magnetic field stabilizes the astropause. The feature of a smooth astropause is mainly seen in heliospheric simulations (for example Pogorelov et al 2017a) and in the 3D MHD astrosphere simulations by Katushkina et al (2018) and Gvaramadze et al (2018). Most of the instabilities are discussed in detail for the heliosphere, a special astrosphere.…”

Transition from the Unipolar Region to the Sector Zone: Voyager 2, 2013 and 2014

“…Second, the sector structure was not periodic, since the "sizes" (durations) of sectors varied. It is also possible that therewere ripples on the current sheet (Burlaga & Ness 1994), and we should allow for the possibility that the HCS might be patchy as a result of magnetic reconnection on theoretical grounds (Pogorelov et al 2017). …”