The Release and Propagation of Near-Relativistic Electrons During the April 2002 Sun-Earth Connection Events

Details The Release and Propagation of Near-Relativistic Electrons During the April 2002 Sun-Earth Connection Events The Release and Propagation of Near-Relativistic Electrons During the April 2002 Sun-Earth Connection Events

Dec 2002

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002agufmsa12a..04s&link_type=abstract

American Geophysical Union, Fall Meeting 2002, abstract #SA12A-04

Physics

2704 Auroral Phenomena (2407), 2784 Solar Wind/Magnetosphere Interactions, 7513 Coronal Mass Ejections

Scientific paper

Relativistic solar electrons can play a role in the magnetospheric-ionosphere system response. Because their transit time to Earth is little more than 10 minutes, detailed knowledge of their acceleration, injection, and propagation mechanisms is critical to establishing a causality chain to the Earth's upper atmosphere. The time period 14-24 April 2002 contains two periods of high intensities (~106/cm2s.sr.MeV) of near-relativistic electrons (38-315 keV) measured by the EPAM experiment on the ACE spacecraft that we can use to probe the causality of this response. First, on April 17 near-relativistic electrons were injected in association with flare and coronal mass ejection (CME) activity (2N/M1.2 flare S14W34 at 07:46 UT). By coincidence, an interplanetary shock passed over ACE less than 3 hours later at 10:21 UT, somewhat enhancing the impulsively injected particles. The electron intensities then decayed over the next day to ~ 3% of their post-shock value. Second, the large west limb activity on 21 April 2002 (2N/M2.6 flare S14W84 at 00:43 UT) was associated with at least three erupting (CMEs), as imaged by LASCO on the SOHO spacecraft. The earliest projected CME launch (extrapolated to 1 Rsun) was at 01:15 UT for the dominant CME in the ecliptic plane, which had a projected speed of 2247 km/sec off the west limb. Electrons were injected promptly into the interplanetary medium when the radial distance of this CME was ~3.5 Rsun), based on the arrival of 175-315 keV electrons at the ACE spacecraft and assuming a path length of 1.2 AU. Unlike the 17 April event, the electron intensities continued to rise by ~300% over the next day, and then decayed only by ~10% when the CME-related shock arrived at ACE at 04:15 UT on 23 April. Consequently, even though the peak intensities of the first and second electron events were comparable, the fluence in the second was much greater (contributing to its increased geo-effectiveness).

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