Near-relativistic Electrons: Corotating Interaction Regions and Particle Reservoirs

Physics

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2102 Corotating Streams, 2114 Energetic Particles, Heliospheric (7514), 2118 Energetic Particles, Solar, 2134 Interplanetary Magnetic Fields, 2139 Interplanetary Shocks

Scientific paper

Ulysses observations in the radial range 3-5 AU (beginning in 1990) revealed two remarkable aspects of the global phenomenology of near-relativistic (40-300 keV) electron propagation in the heliosphere. One was the high intensities of these electrons associated with mid-latitude CIRs [Simnett et al., 1994] during the declining phase of Solar Cycle 22. These intensities peaked at the reverse shock of the CIR and decayed slowly for many days thereafter as the reverse shock corotated away from Ulysses. At higher latitudes (above the last observable reverse shocks), the recurrent electron events persisted, but with a phase lag that implied remote magnetic connection to the CIRs at lower latitudes from greater distances outward [Simnett and Roelof, 1995]. The second phenomenon was the creation of energetic particle "reservoirs" during periods of high solar activity [Roelof et al., 1992; McKibben, 2001] at the maxima of Solar Cycles 22 and 23. The original interpretation was that the outer boundaries of the reservoirs were formed by the merging in the middle heliosphere of the many plasma disturbances (ICMEs) that are launched during the history of great active regions. Field-aligned as well as transverse gradients of both energetic electron and ion intensities within the largest reservoirs are remarkably small, and the decay rate of the intensities can be nearly independent of species, charge, and energy [Reinhard {\ et al.}, 1985; Reames et al., 1997]. In both phenomena, the particles are confined to the inner heliosphere: within reservoirs by mirroring at merged transient magnetic structures, and sunward of CIRs by reflection and acceleration at (and possibly beyond) the corotating reverse shock. Momentum loss plays a major role in the transport of energetic particles inward from the CIRs [Roelof, 2000], and the same must also be true for particles within the reservoirs [Lee, 2000]. In the weak-scattering approximation, the fractional rate of momentum loss is independent of mass, charge, and momentum [Roelof, 2000]. Consequently, a common theoretical framework can describe the propagation of ions as well as electrons associated with both CIRs and reservoirs.

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