A Simulation Study of the Interaction Between a Fast Shock and the Heliopuase

L.C Lee,Y.C Whang,H.J Cai,B.R Schmidt

doi:10.3319/tao.1997.8.3.345(a)

Abstract

In a one-dimensional hybrid simulation of a fast shock impinging on the heliopause (HP), it is found that two regions of increased plasma density are formed between the transmitted and reflected shocks. The region downstream of the shock, on the interstellar side of the heliopause, has typically twice the original plasma density. The density increase is dependent on the impinging shock speed. This region has a greatly enhanced ion temperature anisotropy T(subscript ┴)/T(subscript ∥)-100 and a plasma beta β~0.1-1.0, which may lead to the generation of ion cyclotron waves and mirror waves. The region downstream of the reflected shock, on the solar wind side of the heliopause, has typically a 25% increase in plasma density. The enhanced temperature anisotropy is T(subscript ┴)/T(subscript ∥)~1.2, but the plasma beta is very high, β-20, which may also lead to the generation of mirror waves and ion cyclotron waves.

Highlights

Voyager spacecraft observations of very low frequency radio emissions(2-3.6 kHz) in the outer heliosphere[Kurth et al 1984, Macek et al 1991, Gurnett et al 1993] have recently stirred interest in the termination shock, the outer solar wind, and the heliopause
Burgess and Schwarz [1988] and Wu et al [1993] have simulated the interaction of a fast perpendicular shock with a tangential discontinuity in the solar wind
Mandt and Lee [1991] have simulated the interaction of a weak fast shock with a tangential discontinuity, representing Earth's magnetopause

Summary

INTRODUCTION

Voyager spacecraft observations of very low frequency radio emissions(2-3.6 kHz) in the outer heliosphere[Kurth et al 1984, Macek et al 1991, Gurnett et al 1993] have recently stirred interest in the termination shock, the outer solar wind, and the heliopause. Gurnett et al [1993] proposed that the fast leading shock of a global merged interaction region (GMIR) triggered the observed radio emissions at or near the heliopause, and estimated the distance to the heliopause to be between 116 and 177 AU. Whang and Burlaga [1994] and Whang et al [1995] studied the interaction of an interplanetary MHD shock with the heliopause using an MHD formulation They identified dense plasma regions which could account for the observed radio frequencies and calculated possible locations for the termination shock and heliopause. Burgess and Schwarz [1988] and Wu et al [1993] have simulated the interaction of a fast perpendicular shock with a tangential discontinuity in the solar wind. Mandt and Lee [1991] have simulated the interaction of a weak fast shock with a tangential discontinuity, representing Earth's magnetopause. We simulate the interaction of a fast (GMIR) and the heliopause

SIMULATION MODEL

SIMULATION RESULTS

GENERATION OF MIRROR WAVES AND ION CYCLOTRON WAVES