A theoretical calculation provides inner radiation belt proton intensities as a function of time and of the three adiabatic invariants, M, K, and L, in the kinetic energy range from ∼10 MeV to ∼4 GeV and the L range from 1.1 to 2.4. Long residence times for trapped protons of up to several thousand years require similarly long input time series for the geomagnetic field, solar activity, and solar proton fluences. Additional inputs include galactic cosmic ray spectra, nuclear scattering cross sections, and the neutral and plasma densities in the atmosphere, ionosphere, and plasmasphere. Trapped proton sources are cosmic ray albedo neutron decay (CRAND), calculated from a Monte Carlo particle transport simulation, and solar proton injection using a derived empirical injection efficiency that is ∼10−4 at 10 MeV. Radial diffusion provides inward transport of injected solar protons. Calculated intensities at energies ≲100 MeV and for L ≳ 1.3 are dominated by solar protons, CRAND being the dominant source otherwise. Losses are by ionization of the neutral atmosphere, energy transfer to plasma electrons, and inelastic nuclear scattering. Numerical trajectory tracing determines trapping limits and drift shell averages of the albedo neutron intensity and of neutral and plasma densities for loss rate calculations. Geomagnetic secular variations cause adiabatic energy and drift shell changes. Intensities are greater than they would be in a constant geomagnetic field by factors up to ∼10, a result of long proton residence times and the presently decreasing geomagnetic dipole moment.

[1] The extraordinary period from late October through early November 2003 was marked by more than 40 coronal mass ejections (CME), eight X-class flares, and five large solar energetic particle (SEP) events. Using data from instruments on the ACE, SAMPEX, and GOES-11 spacecraft, the fluences of H, He, O, and electrons have been measured in these five events over the energy interval from $0.1 to >100 MeV/nucleon for the ions and $0.04 to 8 MeV for electrons. The H, He, and O spectra are found to resemble double power laws, with a break in the spectral index between $5 and $50 MeV/nucleon which appears to depend on the charge-to-mass ratio of the species. Possible interpretations of the relative location of the H and He breaks are discussed. The electron spectra can also be characterized by double power laws, but incomplete energy coverage prevents an exact determination of where and how the spectra steepen. The proton and electron fluences in the 28 October 2003 SEP event are comparable to the largest observed during the previous solar maximum, and within a factor of 2 or 3 of the largest SEP events observed during the last 50 years. The 2-week period covered by these observations accounted for $20% of the high-energy solar-particle fluence over the years from 1997 to 2003. By integrating over the energy spectra, the total energy content of energetic protons, He, and electrons in the interplanetary medium can be estimated. After correcting for the location of the events, it is found that the kinetic energy in energetic particles amounts to a significant fraction of the estimated CME kinetic energy, implying that shock acceleration must be relatively efficient in these events.

Abstract. Observations from the High Sensitivity Telescope (HIST) on Polar made around January and May 1998 are used to constrain the source location of outer radiation belt relativistic electrons. Phase space densities calculated as a function of the three adiabatic invariants show positive radial gradients for L < 4, suggestive of no source in that region. In particular, the peak intensity near L--3 of a large enhancement beginning on May 4, 1998, appears to have been formed by inward transport over a period of several days. For L > 4, peaks in the radial dependence of the phase space density are suggestive of a local electron source that may be nonadiabatic acceleration or pitch angle scattering. However, discrepancies in the results obtained with different magnetic field models and at different local times make this a tentative conclusion.

Abstract. The role of high-speed solar wind streams in driving relativistic electron acceleration within the Earth's magnetosphere during solar activity minimum conditions has been well documented. The rising phase of the new solar activity cycle (cycle 23) commenced in 1996, and there have recently been a number of coronal mass ejections (CMEs) and related "magnetic clouds" at 1 AU. As these CME/cloud systems interact with the Earth's magnetosphere, some events produce substantial enhancements in the magnetospheric energetic particle population while others do not. This paper compares and contrasts relativistic electron signatures observed by the POLAR, SAMPEX, Highly Elliptical Orbit, and geostationary orbit spacecraft during two magnetic cloud events: May 27-29, 1996, and January 10-11, 1997. Sequences were observed in each case in which the interplanetary magnetic field was first strongly southward and then rotated northward. In both cases, there were large solar wind density enhancements toward the end of the cloud passage at 1 AU. Strong energetic electron acceleration was observed in the January event, but not in the May event. The relative geoeffectiveness for these two cases is assessed, and it is concluded that large induced electric fields (9B/9t) caused in situ acceleration of electrons throughout the outer radiation zone during the January 1997 event.

A survey of 27 to 45 MeV proton measurements from the HEO‐3 satellite during the years 1998 through 2005 has been taken to describe variability in the outer part of the inner radiation belt and slot region (L = 2 to 3). Rapid (∼1‐day) changes are described as injection or loss events, characterized respectively by Gaussian or exponential L dependencies. The radial extent of both event types is correlated to the minimum Dst of associated magnetic storms, while the injection magnitude is correlated to the flux of associated interplanetary solar proton events. Changes in the maximal L of observed trapped protons are consistent with trapping limits estimated from magnetic field line curvature. The inward extent and energy independence of the observed loss events are inconsistent with field line curvature induced scattering in a static magnetic field. However, time‐dependent geomagnetic cutoff suppression, observed during magnetic storms, may be the cause of significant losses. Drift resonance with electric field impulses caused by rapid magnetospheric compression is the likely cause of both solar proton injections and radial shifts of preexisting trapped protons.

[1] Based on SAMPEX/PET observations, the rates and the spatial and temporal variations of electron loss to the atmosphere in the Earth's radiation belt were quantified using a drift diffusion model that includes the effects of azimuthal drift and pitch angle diffusion. The measured electrons by SAMPEX can be distinguished as trapped, quasi-trapped (in the drift loss cone), and precipitating (in the bounce loss cone). The drift diffusion model simulates the low-altitude electron distribution from SAMPEX. After fitting the model results to the data, the magnitudes and variations of the electron lifetime can be quantitatively determined based on the optimum model parameter values. Three magnetic storms of different magnitudes were selected to estimate the various loss rates of ∼0.5-3 MeV electrons during different phases of the storms and at L shells ranging from L = 3.5 to L = 6.5 (L represents the radial distance in the equatorial plane under a dipole field approximation). The storms represent a small storm, a moderate storm from the current solar minimum, and an intense storm right after the previous solar maximum. Model results for the three individual events showed that fast precipitation losses of relativistic electrons, as short as hours, persistently occurred in the storm main phases and with more efficient loss at higher energies over wide range of L regions and over all the SAMPEX-covered local times. In addition to this newly discovered common feature of the main phase electron loss for all the storm events and at all L locations, some other properties of the electron loss rates, such as the local time and energy dependence that vary with time or locations, were also estimated and discussed. This method combining model with the low-altitude observations provides direct quantification of the electron loss rate, a prerequisite for any comprehensive modeling of the radiation belt electron dynamics.

[1] The dynamics of inner radiation belt electrons are governed by competing source, loss, and transport processes. However, during the recent extended solar minimum period the source was inactive and electron intensity was characterized by steady decay. This provided an opportunity to determine contributions to the decay rate of losses by precipitation into the atmosphere and of diffusive radial transport. To this end, a stochastic simulation of inner radiation belt electron transport is compared to data taken by the IDP instrument on the DEMETER satellite during 2009. For quasi-trapped, 200 keV electrons at L = 1.3, observed in the drift loss cone (DLC), results are consistent with electron precipitation losses by atmospheric scattering alone, provided account is taken of non-diffusive wide-angle scattering. Such scattering is included in the stochastic simulation using a Markov jump process. Diffusive small-angle atmospheric scattering, while causing most of the precipitation losses, is too slow relative to azimuthal drift to contribute significantly to DLC intensity. Similarly there is no contribution from scattering by VLF plasma waves. Energy loss, energy diffusion, and azimuthal drift are also included in the model. Even so, observed decay rates of stably-trapped electrons with L < 1.5 are slower than predicted by scattering losses alone, requiring radial diffusion with coefficient D LL $ 3 Â 10 À10 s À1 to replenish electrons lost to the atmosphere at low L values.

[1] A numerical model of the low-altitude energetic electron radiation belt, including the effects of pitch angle diffusion into the atmosphere and azimuthal drift, predicts lifetimes and longitude-dependent loss rates as a function of electron energy and diffusion coefficient. It is constrained by high-altitude ($20,000 km) satellite measurements of the energy spectra and pitch angle distributions and then fit to low-altitude ($600 km) data that are sensitive to the longitude dependence of the electron losses. The fits provide estimates of the parameterized diffusion coefficient. The results show that the simple driftdiffusion model can account for the main features of the low-altitude radiation belt inside the plasmasphere during periods of steady decay. The rate of pitch angle diffusion is usually stronger on the dayside than on the nightside, frequently by a factor $10. The average derived lifetimes for loss into the atmosphere of $10 days are comparable to the observed trapped electron decay rates. Considerable variability in the loss rates is positively correlated with geomagnetic activity. The results are generally consistent with electron scattering by plasmaspheric hiss as the primary mechanism for pitch angle diffusion.