Stream Interaction Regions and Interplanetary Coronal Mass Ejections at 5 AU

Details Stream Interaction Regions and Interplanetary Coronal Mass Ejections at 5 AU Stream Interaction Regions and Interplanetary Coronal Mass Ejections at 5 AU

May 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007agusmsh23a..04j&link_type=abstract

American Geophysical Union, Spring Meeting 2007, abstract #SH23A-04

Physics

2101 Coronal Mass Ejections (7513), 2102 Corotating Streams, 2111 Ejecta, Driver Gases, And Magnetic Clouds, 2134 Interplanetary Magnetic Fields, 2139 Interplanetary Shocks

Scientific paper

Two major types of large-scale solar wind structures, stream interaction regions (SIRs) and interplanetary coronal mass ejections (ICMEs) are observed in the heliosphere. Both types of structures evolve as they propagate out from the Sun. Using Ulysses SWOOPS and VHM/FGM observations near 5 AU within +/- 10 degrees of the solar ecliptic plane, we have completed surveys of these two types of structures in 1992, 1997- 1998, and 2003-2005, which cover different phases of the solar activity cycle. About 70 precent of the SIRs in our survey are associated with shocks, many of which are reverse shocks. As at 1 AU, magnetic field and total perpendicular pressure (Pt) signatures are prominent for most SIRs, but some plasma signatures (e.g., a gradual and monotonic increase of velocity, a compression of proton number density, and a sharp increase of proton temperature) are not always apparent at larger radial distances. Most SIRs do not have sharp stream interfaces. The majority of ICMEs drive leading forward shocks. In previous work, we found 1 AU ICME observations could be sorted roughly into three categories, based on the temporal profile of Pt, and we interpreted the different categories as indicators of the impact parameter of the spacecraft with respect to the central causative flux rope. At 5 AU, we find such a sorting can not be applied to quite a few ICMEs, indicating ICMEs become more complicated as they propagate. In contrast with 1 AU ICMEs, several ICMEs seem to contain more than one flux rope, and these ropes differ in size, field strength, and even plasma content. Such events may be caused by the interaction of separate CMEs from the Sun, or may contain flux ropes formed by reconnection at the heliospheric current sheet between the Sun and 5 AU. Frequently, ICMEs and SIRs are merged and hard to separate. The number of such combined events decreases as solar activity declines. We quantitatively examine the occurrence rate, shock association rate, radial extent, and expansion velocity of these two types of solar wind disturbances and compare their behavior as a function of solar cycle and also with 1 AU Wind and ACE observations we have previously compiled in 2006 Solar Physics papers.

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