Shock-induced Trapping of Solar Energetic Particles in the Earth's Magnetosphere

The recent SAMPEX report of prompt trapping of solar energetic Fe at L=2 in association with a Storm Sudden Commencement (SSC) during the Bastille Day 2000 event¹ has led to examination of other recent Solar Energetic Particle (SEP) trapping events, which include two in November 2001 with trapped Fe signatures. While the the November 6 storm had a larger -Dst value (-277 vs. -213 nT), the second storm was preceeded by a strong SSC impulse (+ 20 nT hourly averaged preliminary Dst), known to be a necessary condition for shock trapping of SEPs^2,3. Other necessary conditions for radial transport by a magnetopause compression-induced electric field impulse are examined. Both November SEP trapping events were characterized by an ICME shock speed exceeding 1200 km/s and > 10 MeV GOES proton fluxes exceeding 10⁴. The larger Dst value for the earlier event is likely to affect the minimum cutoff latitude and minimum L-value of the SEP source population⁴. Coupled MHD-guiding center test particle simulations of the November 24 storm injection are compared with those of the Bastille Day event. Solar wind conditions, the minimum L-value and time scale for trapping in the magnetosphere are examined. The rarity of such events for electrons is also explained. [1]Lorentzen et al., {JGR}, in press, 2002. [2] Li et al., {GRL, 20,} 2423, 1993. [3]Hudson et al., {GRL, 22,} 291, 1995; {JGR, 102}, 14,087, 1997. [4]Leske et al., {JGR, 106, 30,001, 2001}