Characteristics of the interplanetary coronal mass ejections in the heliosphere between 0.3 and 5.4 AU

Abstract

[1] We identify and characterize interplanetary coronal mass ejections (ICMEs) observed by spacecraft in the solar wind, namely Helios 1 and 2, PVO, ACE, and Ulysses, which together cover heliocentric distances from 0.3 to 5.4 AU. The primary identification signature used to look for ICMEs is abnormally low proton temperatures. About 600 probable ICMEs were identified from the solar wind plasma and magnetic field data from these spacecraft. We use these events to study the radial evolution of ICMEs between 0.3 and 5.4 AU, mainly in a statistical sense. The occurrence rate of ICME approximately follows the solar activity cycle. ICMEs expand as they move outward since the internal pressure is generally larger than the external pressure. The average radial width of ICMEs increases with distance. ICMEs expand by a factor of 2.7 in radial width between 1 and 5 AU. The radial expansion speed of ICMEs decreases with distance and is of the order of the Alfvén speed. The density and magnetic field magnitude decrease faster in ICMEs, which fall off with distance R as R À2.4 and R À1.5 , respectively, than in the ambient solar wind; however, the temperature decreases as R À0.7 , slightly less rapid than in the ambient solar wind. These results are consistent with previous findings with relatively limited data coverage. We also use a one-dimensional MHD model to investigate the radial expansion of the ICMEs and find that the radial expansion speed is of the order of the Alfvén speed, consistent with the observations.

The radial width of a Coronal Mass Ejection between 0.1 and 0.4 AU estimated from the Heliospheric Imager on STEREO

“…This exponent value is consistent within 2 standard deviations of previous results (shown in Fig. 6) produced from statistical surveys from multiple spacecraft over 0.3-5 AU carried out by Bothmer et al (1998) and later by Liu et al (2004) and Wang et al (2005) with a larger data set. A theoretical calculation was also carried out by Chen (1996) that yielded a power law with an exponent of 0.88.…”

“…The data is displayed in a loglog plot to produce a linear best fit curve. As CME radial sizes predominantly increase with increasing distance albeit at a slower rate as they progress through the heliosphere, a power law has commonly been used to depict the relationship determined from in situ observations (Bothmer and Schwenn, 1994;Wang et al, 2005). Applying power laws to our results presented in Fig.…”

“…For example, an ICME may expand simply because the leading edge was ejected from the Sun at a speed greater than the trailing edge (Gosling et al, 1998;Tripathi et al, 2006). The expansion of ICMEs in the anti-sunward direction has previously been quantified using statistical surveys from multiple spacecraft over a distance range of 0.3 to 5.4 AU from the Sun (Bothmer and Schwenn, 1994;Liu et al, 2004;Wang et al, 2005). These studies have estimated the radial expansion in the form of a power law variation of CME radial width as a function of heliocentric distance.…”

Energetic particles detected by the Electron Reflectometer instrument on the Mars Global Surveyor, 1999–2006

“…More recently, Zeitlin et al [2010] summarized solar particle events and galactic cosmic rays (GCRs) recorded by several instruments on Mars Odyssey between 2002 and 2006. Efforts are also underway to understand the propagation of ICMEs to the outer heliosphere using a variety of observations from multiple spacecraft including Ulysses, WIND, Voyager, and Pioneer [Gazis et al, 2006;Liu et al, 2005;Richardson et al, 2006;Steiger and Richardson, 2006;Wang et al, 2005].…”

Assessing the Effect of Spacecraft Motion on Single-Spacecraft Solar Wind Tracking Techniques

“…For more information on CMEs and CIRs see e.g. Burlaga, Harvey, and Sheeley (2001) and Wang (2005). In this study we will consider the retrieval of direction and velocity information of CMEs and CIRs from SECCHI observations.…”