[1] We examined and simulated the dynamics of energetic electrons during the October 2001 magnetic storm with the relativistic RAM electron model for a wide range of energies. The storm had a rapid main phase followed by a day of strong geomagnetic activity that produced a second Dst minimum and then a very quiet recovery phase. During the main phase and the period of intense activity, the observed hot electron flux (E = 30 keV) increased at low L while decreasing at large L and then decayed abruptly at the beginning of the recovery phase when activity subsided. The flux of subrelativistic (E = 100-300 keV) electrons also increased at low L and decreased at large L during the main phase and the period of intense activity but remained high throughout the recovery phase. In contrast, the relativistic (E = 300-1200 keV) electron flux decreased during the main phase, remained low throughout the period of intense activity, and then increased above prestorm values during the recovery phase in spite of the low activity. The highest energy electron flux (E > 1200 keV) decreased during the main phase and never recovered to prestorm levels. The numerical simulation was compared with observations. We identified the physical processes which produce the flux variations at the different energies. In the simulation, the hot electrons were convected inward during the main phase, reproducing the observed local time flux asymmetry. The higher-energy electrons, on the other hand, were predominantly transported inward by radial diffusion and not convective motion. The simulation was not able to reproduce the subrelativistic and relativistic electron flux enhancement and spatial expansion as observed during the recovery phase. In the simulation, most of the energization occurred around the main phase and the period of intense activity with negligible transport or flux enhancement during the recovery phase. The discrepancy between the observed and simulated high energy electron flux suggests that only convective transport and radial diffusion cannot fully explain the electron dynamics. An additional mechanism may be necessary to explain enhancements of high energy electron flux during the recovery phase of the storm.

Long‐term variations of energetic particles in the radiation belts were examined using data from the NOAA (1979–2003) satellites. A significant flux variation with solar cycle was detected together with both semiannual and recurrent flux variations. It was revealed that the phase of flux variations for the solar cycle depends on both particle energy and distance from the Earth; the outer belt shifted inward during the solar active period and outward during the solar quiet period. The numerical simulation for radial diffusion reproduced the flux variation and the outer belt shift qualitatively and suggested that radial diffusion is a major control parameter for the long‐term variations of the inner portion of the outer belt. On the other hand, the simulation did not reproduce the variation of the outer portion of the outer belt, suggesting that further physical processes should be considered.

[1] Two sources of auroral kilometric radiation (AKR) and their development prior to and during substorms were identified from high-time-resolution spectrograms provided by Polar/PWI ac electric field observations and were investigated in connection with the auroral acceleration process. One source is a low-altitude source region corresponding to middle-frequency AKR (MF-AKR), and the other is a high-altitude source region corresponding to low-frequency AKR (LF-AKR). The former appears during the substorm growth phase in the altitude range of 4000-5000 km and is active both before and after substorm onset. A few minutes before the onset, the intensity of this source gradually increases, showing precursor-like behavior. It does not change drastically at the onset and is mostly insensitive to it. At Pi 2 onset, in contrast, high-altitude AKR appears abruptly with intense power in a higher and wider altitude range of 6000 to 12,000 km. The increase in its power is explosive (increasing 1000 times within 20 s), suggesting the abrupt growth of the parallel electric fields that cause bursty auroral electron beams. The statistically derived probability of both sources existing at substorm onset is $70%, indicating that this duality of AKR sources is a common feature of substorms. The highaltitude source and related transient acceleration at substorm onset are apparently due to (1) intrinsically local instabilities such as current-driven instabilities or (2) transient short wavelength Alfvén waves coming from the magnetosphere. The low-altitude source, which is fairly stable and insensitive to substorm onset, may belong to the global quasistatic potential distribution over the auroral oval, which involves a large-scale inverted-V structure and a quasi-steady field-aligned current.

Evolution of energetic electron fluxes, related solar wind conditions, and relevant plasma waves in the inner magnetosphere are examined during the two corotating interaction region (CIR)‐driven magnetic storms in November 1993. In this paper we focus on the fact that the flux of the outer radiation belt electrons increased significantly during the 3 November storm, while it did not increase above the prestorm level during the 18 November storm. The recovery phase of the 3 November storm is associated with the prolonged substorm activity; continuous injections of hot and subrelativistic electrons, and enhanced chorus wave activity which can accelerate subrelativistic electrons to MeV energies by means of wave‐particle interactions. In contrast, the recovery phase of the 18 November storm is associated with reduced substorm activity, weak injections of hot and subrelativistic electrons, and low chorus wave activity. These differences in the recovery phase can be related to the southward offset of interplanetary magnetic field (IMF) in the high‐speed coronal hole stream, which is influenced by the IMF sector polarity via the Russell‐McPherron effect (dipole tilt effect associated with the IMF polarity).

[1] The sudden formation of parallel electric fields in the magnetosphere-ionosphere (M-I) coupling system is essential to complete substorm onset. From this standpoint, we focus substorm ignition on field-aligned acceleration by studying the dynamical behavior of auroral kilometric radiation. Field-aligned auroral acceleration shows a distinct two-step evolution at substorm onset: the activation of low-altitude acceleration (h ∼ 4000-5000 km) which corresponds to auroral initial brightening and the subsequent abrupt breakout of high-altitude acceleration (h ∼ 6000-12,000 km) which corresponds to auroral breakup. Cases when only low-altitude acceleration (first-step evolution) is activated are pseudosubstorms. This indicates that the second evolution of field-aligned acceleration divides full substorm from pseudosubstorm. The statistical relationship between the plasma flow burst in the plasma sheet and its response to the M-I coupling region shows that about 65% of flow bursts cause pseudobreakup/initial brightening (low-altitude acceleration) and one third of them develops into full substorm (low-altitude and highaltitude accelerations), while the magnitude of flow velocity does not necessarily distinguish between pseudobreakup and full substorm. This suggests that some plasma flow bursts originate field-aligned current which first enhance low-altitude acceleration, and the increasing field-aligned current induces second acceleration above the preexisting low-altitude acceleration as a consequence of current/current-driven instabilities. In this sense, the substorm is finally ignited in the auroral M-I coupling region.