Magnetic topology of coronal mass ejection events out of the ecliptic: Ulysses/HI-SCALE energetic particle observations

O E Malandraki,E T Sarris,G Tsiropoula

doi:10.5194/angeo-21-1249-2003

Abstract

Abstract. Solar energetic particle fluxes (Ee > 38 keV) observed by the ULYSSES/HI-SCALE experiment are utilized as diagnostic tracers of the large-scale structure and topology of the Interplanetary Magnetic Field (IMF) embedded within two well-identified Interplanetary Coronal Mass Ejections (ICMEs) detected at 56° and 62° south heliolatitudes by ULYSSES during the solar maximum southern high-latitude pass. On the basis of the energetic solar particle observations it is concluded that: (A) the high-latitude ICME magnetic structure observed in May 2000 causes a depression in the solar energetic electron intensities which can be accounted for by either a detached or an attached magnetic field topology for the ICME; (B) during the traversal of the out-of-ecliptic ICME event observed in July 2000 energetic electrons injected at the Sun are channeled by the ICME and propagate freely along the ICME magnetic field lines to 62° S heliolatitude.Key words. Interplanetary physics (energetic particles; interplanetary magnetic fields)

Highlights

The topology of magnetic field lines carried into the interplanetary medium by coronal eruptive events has been investigated for several decades. Cocconi et al (1958) and Gold (1959) suggested the presence of huge magnetic loops that could retain their connection to the Sun and extend to distances beyond the Earth’s orbit
Their gyroradii are small compared to Interplanetary Coronal Mass Ejections (ICMEs) scale sizes, while their speeds are very much greater than ICME speeds. They propagate nearly “scatter-free” in the unshocked Interplanetary Magnetic Field (IMF), i.e. with negligible cross field diffusion and large mean free paths along the field. These propagation characteristics provide the means for tracing the large-scale structure of ICMEs by unraveling observations of the angular distributions of the intensities of the energetic particles during the ICME passage (Sarris and Krimigis, 1982)
An abrupt depression in the low-energy electron intensities that interrupted the solar electron event decay phase has been observed by ULYSSES during the passage of the highlatitude ICME detected at 56◦ south heliolatitude in May 2000

Summary

Introduction

The topology of magnetic field lines carried into the interplanetary medium by coronal eruptive events has been investigated for several decades. Cocconi et al (1958) and Gold (1959) suggested the presence of huge magnetic loops that could retain their connection to the Sun and extend to distances beyond the Earth’s orbit. The observation of a 3-h long abrupt depression in the event flux profile with bi-directional electron anisotropy signatures throughout it indicated that injected particles at the Sun, could not enter this ICME portion which was concluded to be disconnected from the Sun exhibiting a plasmoid topology This event, observed near solar maximum during the second ULYSSES southerly high-latitude pass, constitutes the first observation of an out-of-ecliptic ICME event comprising complex intertwined structures that include regions both connected to and disconnected from the Sun. In this work, we use solar energetic electron fluxes (Ee ≥ 38 keV) observed by the ULYSSES/HI-SCALE instrument, in order to probe the internal magnetic structure of two well-identified ICME events detected at 56◦ (May 2000) and 62◦ (July 2000) south heliographic latitudes during the ULYSSES second ascent to southern high-latitude regions of the heliosphere. The still unsolved problem of whether ICMEs have been detached from the solar corona or are still magnetically anchored to it when they arrive at the spacecraft is rigorously tackled

Instrumentation

Observations and data analysis

Summary and conclusions