Response of the termination shock to interplanetary disturbances: 2. MHD

Abstract

Abstract.The interaction of the solar wind termination shock with disturbances incident from the upstream solar wind is considered using a one-dimensional MHD (both transverse and oblique) model. This paper extends the work of Story and Zank [1995] (Paper 1) to include the effects of the interplanetary magnetic field. A decay law is derived to describe the damping of compound rarefaction/shock structures.The inclusion of a parallel magnetic field component leads to the production of slow-mode rarefactions and shocks. Therefore, depending on parameters, the interaction of the termination shock with interplanetary disturbances may serve to generate both slow-and fast-mode magnetosonic waves that propagate through the heliosheath. Furthermore, it follows from the simulations presented here that slow-mode waves and rotational discontinuities can be expected to occur, at least to some extent, at any region of the solar system where collisions between oblique MHD shocks occur. Some discussion regarding the relative local orientation of the heliospheric magnetic field, with respect to the interstellar magnetic field, is presented to address the possibility of a global rotational discontinuity(s) which may be necessary to connect the interplanetary magnetic field to the interstellar field. Some further results concerning the interaction of waves and shocks reflected from heliosheath structure with the termination shock are also presented.

Pressure Pulses at Voyager 2: Drivers of Interstellar Transients?

“…The top panel of Figure 2 shows that the sunspot number jumps upward in 2011; since the transit time of the solar wind to V2 is of the order of a year, the onset of these MIRs is likely due to the solar cycle increase in solar activity as occurred in the last solar maximum (Figure 1). , the plasma V R , N, T, and P all increase in the heliosheath MIRs, consistent with model predictions (Steinolfson & Gurnett 1995;Story & Zank 1997;Zank & Muller 2003;Washimi et al 2007Washimi et al , 2011. In the 2002 MIRs V R , N, and P increase but T does not.…”

“…Model predictions are also consistent with this interpretation; large ram pressure increases in the solar wind drive the termination shock outward and generate high ram and thermal pressure pulses that propagate through the heliosheath (Steinolfson & Gurnett 1995;Story & Zank 1997;Zank & Muller 2003;Washimi et al 2007Washimi et al , 2011Washimi et al , 2012Zank 2015). These pressure pulses may be partially reflected near the heliopause and again encounter the termination shock, moving it inward (Washimi et al 2007(Washimi et al , 2011.…”

Faltering Steps Into the Galaxy: The Boundary Regions of the Heliosphere

“…The speed of the pulse in the heliosheath near the HTS is almost the same as that of the ram-pressure pulse in interplanetary space. Because the speed of these pulses is almost equal to the magnetosonic speed, they may be identified as magnetosonic pulses (Story & Zank 1997). These pulses are partially reflected near the HP, back toward the TS, with which they then collide, causing a substantial decrease in R TS .…”

“…The HTS position moves out radially after a SW high-ram-pressure structure collision. Large-amplitude pulses in the ram pressure, thermal pressure, temperature, density, and magnetic pressure are generated downstream of the HTS (Story & Zank 1997, Zank & Müller 2003, Washimi et al 2007, and each pulse propagates into the IHS. The speed of the pulse in the heliosheath near the HTS is almost the same as that of the ram-pressure pulse in interplanetary space.…”

A Forecast of the Heliospheric Termination-Shock Position by Three-dimensional MHD Simulations

“…Global simulations for a stationary outer heliosphere have been developed over the past two decades (e.g., Baranov & Malama 1993;Heerikhuisen et al 2006;Izmodenov et al 2005;Linde et al 1998;Matsuda et al 1989;Muller et al 2000;Opher et al 2006;Pogorelov et al 2004Pogorelov et al , 2007Ratkiewicz et al 2000;Usmanov & Goldstein 2006;Washimi & Tanaka 1996;Zank et al 1996), together with a few nonstationary models (e.g., Florinski et al 2005;Karmesin et al 1995;Story & Zank 1997;Tanaka & Washimi 1999;Whang et al 2006;Zank & Muller 2003). However, realistic and time-varying simulations for outer heliosphere phenomena have only recently been attempted (e.g., Intriligator et al 2005;Izmodenov et al 2007;Richardson et al 2006;Wang & Belcher 1999;Washimi et al 2006Washimi et al , 2007.…”