Characteristics Of The Propagation And Evolution Of Interplanetary Coronal Mass Ejections In The Heliosphere

Coronal mass ejections, through their interplanetary counterparts (ICME),often trigger geomagnetic storms, making them of great importance to spaceweather studies and improved forecasting enterprise.We identify and characterize interplanetary mass ejections (ICME) observedby multiple spacecraft such as Helios 1 and 2, PVO, ACE and Ulysses, whichtogether cover heliocentric distance from 0.3 to 5.4 AU. An abnormally low protontemperature is used as the primary identification signature of ICME. About 600probable ICME (162 probable ICME between 0.3 and 1 AU observed by Heliosfrom 1974 to 1980, 114 probable ICME at 0.72 AU observed by PVO from 1979to 1988, 184 probable near-Earth ICME observed by ACE from 1997 to 2003and 136 probable ICME between 1 and 5.4 AU observed by Ulysses from 1990 to2003, where 76 events observed at high latitudes) have been identified from thesolar wind plasma and magnetic field data. The ICME list is used to study theradial evolution of ICME.The chance of an interplanetary coronal mass ejection (ICME) observed bywidely-separated spacecraft is rare. However, such an event provides us a goodopportunity to study the propagation and evolution of ICMEs in the heliosphere.On day 72 of 1975 an ICME was observed by Helios 1 at 0.3 AU, while a similarsolar wind structure was observed by IMP 8 at Earth on day 70 of 1975. On thebasis of comparison of the plasma signatures and the transit time from Helios 1to IMP 8, we hypothesize the observed ICMEs by both spacecraft are resultedfrom the same active region on the solar surface. We use a one-dimensional MHDmodel to track the ICME from Helios 1 (0.3 AU) to Earth. The observed plasmaprofiles and timing are close to those predicted by our MHD model and give thesupports.A magnetic cloud event observed by ACE at Earth on March 4-6, 1998 istracked from the location of ACE to Ulysses. Using a one-dimensional MHD solarwind model, we propagate the ACE data to the location of Ulysses, and confirm that the two magnetic clouds observed by both spacecraft have the same solarorigin. The Grad-Shafranov (GS) reconstruction technique is then employed torecover the 2(1/2)-D cross sections of the magnetic clouds at locations of ACE andUlysses, respectively. The magnetic clouds observed at ACE and Ulysses bothshow magnetic flux-rope configurations of the same chirality and unidirectionalaxial magnetic field along approximately the same direction. It is found that themagnetic cloud is expanding while propagating outward. Their relevant toroidal(axial) and poloidal magnetic flux contained within each flux rope are differentbut approximately of the same order of magnitude. However, the relative mag-netic helicity contained in each flux rope differs significantly. We discuss thecauses of such differences, taking into account the underestimate of the area ofthe flux rope at Ulysses, and the effect of magnetic cloud evolution that may notbe fully addressed by 2-D models.We combine lists from the inner and outer heliosphere between 0.3 and 30AU to perform a statistical study of ICMEs observed by multi-spacecraft suchas Helios, PVO, ACE, Ulysses and Voyager 2. The occurrence rate of ICMEsapproximately follows the solar activity cycle. The radial widths of ICMEs in-crease with distance out to about 15 AU. Beyond that distance the radial widthis roughly constant. The radial expansion speed of the ICMEs is of the orderof the Alfv′en speed. The density and magnetic field magnitude decrease fasterin ICMEs than in the ambient solar wind but the temperature decreases moreslowly than in the ambient solar wind. A one-dimensional MHD numerical codeis also employed to model the propagation of ICME to try to understand theobservations. The model results reproduce the basic expansion characteristics ofICMEs.