Heliopause Stability

Interaction of the supersonic wind with the supersonic flow of the interstellar medium results in the development of interaction region called the heliospheric interphase. It is bounded by two shocks, termination and bow. The solar wind flow compressed at the termination shock and the interstellar medium flow compressed at the bow shock are separated by a tangential discontinuity called the heliopause. An important problem related to the physical processes in the heliosphere is the heliopause stability. We present a brief review of studies of two types of instabilities that can operate at the heliopause: the Kelvin-Helmholtz (KH) instability of the heliopause flanks and the Rayleigh-Taylor instability of the part of heliopause close to the apex point. Using the local analysis the stability of the magnetic-free heliopause flanks was considered, and then the effect of the magnetic field in the interstellar medium and solar wind was discussed. The RT instability in the vicinity of the apex point can be driven by the accelerated motion of the heliospheric interface toward the interstellar medium. It was studied both in the case of constant acceleration as well as acceleration oscillating with the period of the solar cycle. Another mechanism of driving the RT instability is the charge exchange between the hydrogen atoms and ions. This kind of instability was studied for the magnetic-free heliopause.