ICMEs in the Outer Heliosphere and at High Latitudes: An Introduction

Interplanetary coronal mass ejections (ICMEs) are observed at all latitudes and distances from which data are available. We discuss the radial evolution of ICMEs out to large distances and ICME properties at high latitudes. The internal pressure of ICMEs initially exceeds the ambient solar wind pressure and causes the ICMEs to expand in radial width to about 15~AU. Large ICMEs and series of ICMEs compress the leading plasma and form merged interaction regions (MIRs) which dominate the structure of the outer heliosphere at solar maximum. The distribution of high-latitude ICMEs is solar cycle dependent. A few overexpanding ICMEs are observed at high-latitude near solar minimum. Near solar maximum ICMEs are observed at all latitudes, but those above 40° do not have high charge states.