[1] Loss mechanisms responsible for the sudden depletions of the outer electron radiation belt are examined based on observations and radial diffusion modeling, with L*-derived boundary conditions. SAMPEX data for October-December 2003 indicate that depletions often occur when the magnetopause is compressed and geomagnetic activity is high, consistent with outward radial diffusion for L* > 4 driven by loss to the magnetopause. Multichannel Highly Elliptical Orbit (HEO) satellite observations show that depletions at higher L occur at energies as low as a few hundred keV, which excludes the possibility of the electromagnetic ion cyclotron (EMIC) wave-driven pitch angle scattering and loss to the atmosphere at L* > 4. We further examine the viability of the outward radial diffusion loss by comparing CRRES observations with radial diffusion model simulations. Model-data comparison shows that nonadiabatic flux dropouts near geosynchronous orbit can be effectively propagated by the outward radial diffusion to L* = 4 and can account for the main phase depletions of outer radiation belt electron fluxes.

We have used a unique constellation of Earth‐orbiting spacecraft and ground‐based measurements in order to study a relatively isolated magnetospheric substorm event on August 27, 2001. Global ultraviolet images of the northern auroral region established the substorm expansion phase onset at 0408:19 (±1 min) UT. Concurrent measurements from the GOES‐8, POLAR, LANL, and CLUSTER spacecraft allow us to construct a timeline which is consistent with magnetic reconnection on the closed field lines of the central plasma sheet near XGSM ∼ −18 RE some 7 minutes prior to the near‐earth and auroral region times of substorm expansion phase onset. This suggests that magnetic reconnection (i.e., the substorm neutral line) in this case formed in the mid‐tail region substantially before current disruption, field dipolarization near geostationary orbit, or auroral substorm onsets occurred. Thus, the magnetic reconnection process is interpreted as the causative driver of dissipation in this well‐observed case.

Although the Earth's Van Allen radiation belts were discovered over 50 years ago, the dominant processes responsible for relativistic electron acceleration, transport and loss remain poorly understood. Here we show evidence for the action of coherent acceleration due to resonance with ultra-low frequency waves on a planetary scale. Data from the CRRES probe, and from the recently launched multi-satellite NASA Van Allen Probes mission, with supporting modelling, collectively show coherent ultra-low frequency interactions which high energy resolution data reveals are far more common than either previously thought or observed. The observed modulations and energy-dependent spatial structure indicate a mode of action analogous to a geophysical synchrotron; this new mode of response represents a significant shift in known Van Allen radiation belt dynamics and structure. These periodic collisionless betatron acceleration processes also have applications in understanding the dynamics of, and periodic electromagnetic emissions from, distant plasma-astrophysical systems.

The Dynamic Radiation Environment Assimilation Model (DREAM) was developed to provide accurate, global specification of the Earth's radiation belts and to better understand the physical processes that control radiation belt structure and dynamics. DREAM is designed using a modular software approach in order to provide a computational framework that makes it easy to change components such as the global magnetic field model, radiation belt dynamics model, boundary conditions, etc. This paper provides a broad overview of the DREAM model and a summary of some of the principal results to date. We describe the structure of the DREAM model, describe the five major components, and illustrate the various options that are available for each component. We discuss how the data assimilation is performed and the data preprocessing and postprocessing that are required for producing the final DREAM outputs. We describe how we apply global magnetic field models for conversion between flux and phase space density and, in particular, the benefits of using a self‐consistent, coupled ring current–magnetic field model. We discuss some of the results from DREAM including testing of boundary condition assumptions and effects of adding a source term to radial diffusion models. We also describe some of the testing and validation of DREAM and prospects for future development.

The radiation belts and plasma in the Earth's magnetosphere pose hazards to satellite systems which restrict design and orbit options with a resultant impact on mission performance and cost. For decades the standard space environment specification used for spacecraft design has been provided by the NASA AE8 and AP8 trapped radiation belt models. There are well-known limitations on their performance, however, and the need for a new trapped radiation and plasma model has been recognized by the engineering community for some time. To address this challenge a new set of models, denoted AE9/AP9/SPM, for energetic electrons, energetic protons and space plasma has been developed. The new models offer significant improvements including more detailed spatial resolution and the quantification of uncertainty due to both space weather and instrument errors. Fundamental to the model design, construction and operation are a number of new data sets and a novel statistical approach which captures first order temporal and spatial correlations allowing for the Monte-Carlo estimation of flux thresholds for user-specified percentile levels (e.g., 50th and 95th) over the course of the mission. An overview of the model architecture, data reduction methods, statistics algorithms, user application and initial validation is presented in this paper.

Abstract. The drift ballooning mode (DBM) instability near the inner edge of the plasma sheet (IEPS) is studied further by including a nonstationary earthward flow and flow shear in the analysis. Both equatorial and off-equatorial regions are considered. It is found that the presence of a decelerated earthward flow destabilizes both the M_ and M+ branches of the DBM in a large portion of the current sheet near the IEPS and substantially increases the growth rate of the instability. The flow shear in the prelnidnight sector causes the conventional ballooning mode to weakly subside, while it slightly enhances the growth rate for the Alfv6nic ballooning mode.The combination of the earthward flow and flow shear makes both the Alfv6nic ballooning mode and conventional ballooning mode grow much faster than they would without the flow, giving rise to coupled Alfv6nic slow magnetosonic waves, field-a, ligned currents, and the formation of a current wedge. A synthesis of tail reconnection and cross-tail current disruption scenarios is proposed for the substorm global initiation process: When the fast flow produced by magnetic reconnection in the midtail a. bruptly decelerates at the IEPS, it compresses the plasma populations earthward of the front, transports momentum to them, and pushes them farther earthward. This creates the configuration instability in a large portion of the inner tail magnetic field lines on both the tailward side and earthward side of the braking point. As soon as the ionospheric conductance increases over a threshold level, the auroral electrojet is greatly intensified, which leads to the formation of the substorm current wedge and dipolarization of the magnetic field. This substorm paradigm combines the near-Earth neutral line and near-Earth current disruption scenarios for the initiation of substorms and may also synthesize dynamical processes in the magnetosphere-ionosphere coupling and field line resonance during the substorm onset. We intend to use this global model to explain substorm expansion onsets occurring under the southward interplanetary magnetic field condition.

Recent interpretations of cusp energetic ions observed by the POLAR spacecraft have suggested a new energization process in the cusp [Chen et al., 1997; 1998]. Simultaneous enhancement of H+, He+2, and O>+2 fluxes indicates that they are of solar wind origin. In the present study, we examine H+ and He+2 energy spectra from 20 eV to several 100 keV measured by the Hydra, Toroidal Imaging Mass‐Angle Spectrograph (TIMAS), and Charge and Mass Magnetospheric Ion Composition Experiment (CAMMICE) on POLAR. The combined spectrum for each species is shown to be continuous with a thermal distribution below 10 keV/e and an energetic component above 20 keV/e. Energetic ions with comparable fluxes and a similar spectral shape are commonly observed downstream from the Earth's quasi‐parallel (Q∥) bow shock. In addition to the similarity in the ion spectra, electric and magnetic field noise and turbulence detected in the cusp by the Plasma Wave Instrument (PWI) and Magnetic Field Experiment (MFE) onboard POLAR are similar to the previously reported observations at the bow shock. The waves appear to be coincidental to the cusp energetic ions rather than causal. We suggest that these ions are not accelerated locally in the cusp. Rather, they are accelerated at the Q∥ bow shock and enter the cusp along open magnetic field lines connecting both regions.

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