Properties Of Interplanetary Coronal Mass Ejections Research Articles

V arc interplanetary coronal mass ejections observed with the Solar Mass Ejection Imager

Since February 2003, the Solar Mass Ejection Imager (SMEI) has been observing interplanetary coronal mass ejections (ICMEs) at solar elongation angles ε > 20°. The ICMEs generally appear as loops or arcs in the sky, but five show distinct outward concave shapes that we call V arcs. We expect to observe some V arcs, formed by trailing edges of ICME flux ropes or by leading ICME edges sheared by solar wind (SW) speed gradients at the heliospheric current sheet. We characterize the properties of these V arcs and compare them with average properties of all SMEI ICMEs. The typical V arc speeds argue against a slow MHD shock interpretation for their structures. We estimate the V arc solar source locations and their opening angle dynamics as tests for SW shearing. The first test contradicts but the second supports the SW shearing explanation. The implications of the small number of V arcs observed with SMEI is considered. The point P approximation used to determine the V arc locations and inferred solar source regions is critically examined in Appendix A.

Properties of Interplanetary Coronal Mass Ejections

Interplanetary coronal mass ejections (ICMEs) originating from closed field regions on the Sun are the most energetic phenomenon in the heliosphere. They cause intense geomagnetic storms and drive fast mode shocks that accelerate charged particles. ICMEs are the interplanetary manifestations of CMEs typically remote-sensed by coronagraphs. This paper summarizes the observational properties of ICMEs with reference to the ordinary solar wind and the progenitor CMEs.

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.

Modelling interplanetary CMEs using magnetohydrodynamic simulations

Abstract. The dynamics of Interplanetary Coronal Mass Ejections (ICMEs) are discussed from the viewpoint of numerical modelling. Hydrodynamic models are shown to give a good zero-order picture of the plasma properties of ICMEs, but they cannot model the important magnetic field effects. Results from MHD simulations are shown for a number of cases of interest. It is demonstrated that the strong interaction of the ICME with the solar wind leads to the ICME and solar wind velocities being close to each other at 1 AU, despite their having very different speeds near the Sun. It is also pointed out that this interaction leads to a distortion of the ICME geometry, making cylindrical symmetry a dubious assumption for the CME field at 1 AU. In the presence of a significant solar wind magnetic field, the magnetic fields of the ICME and solar wind can reconnect with each other, leading to an ICME that has solar wind-like field lines. This effect is especially important when an ICME with the right sense of rotation propagates down the heliospheric current sheet. It is also noted that a lack of knowledge of the coronal magnetic field makes such simulations of little use in space weather forecasts that require knowledge of the ICME magnetic field strength.Key words. Interplanetary physics (interplanetary magnetic fields) Solar physics, astrophysics, and astronomy (flares and mass ejections) Space plasma physics (numerical simulation studies)