A radiation belt‐ring current (RB‐RC) forecasting model is presented. This model solves the convection‐diffusion equation of plasma distribution in the 10 keV to a few MeV range. There are four major auxiliary components to the RB‐RC model: a global magnetic field model, an electric field model, a plasma sheet model (plasma source), and a radial diffusion model. All four components are driven by solar wind and interplanetary magnetic field conditions. In this paper, a brief description of the model and input parameters is given. This model has been used to simulate several geomagnetic storms. In particular, the effects of the inductive electric field on the evolution of the radiation belt electron fluxes are investigated in detail via a case study of the 12 August 2000 storm. It is found that, in general, the inductive electric field arising from the time‐varying magnetic field can enhance the flux level around geosynchronous orbit during the recovery phase of the storms. The model is validated through comparing the simulation results with the Los Alamos National Laboratory satellite measurements. Further refinement and improvement of the model is also discussed.
Global, ion equatorial flux distributions and energy spectra are presented from stereoscopic TwoWide-Angle Imaging Neutral-Atom Spectrometers (TWINS) 1 and TWINS 2 energetic neutral atom (ENA) images for two time periods, 29 May 2010, 1330-1430 UT and 26 May 2011, 1645-1715 UT. The first is just after the main phase of a weak (minimum SYM/H ≈ À70 to À80 nT) corotating interaction region-driven geomagnetic storm. The second is during a relatively quiet period. The global ion distributions show multiple spatial peaks that are coincident with peaks in the AE index. The energy spectra have a primary maximum in the 15-20 keV range. Below the energy maximum, the flux is Maxwellian. Above the main maximum, the flux is either significantly below that of a Maxwellian or has a second component with a maximum in the 40-50 keV range. For the 29 May 2010, 1330-1430 UT time period, the flux from the TWINS stereoscopic images is compared to the results from TWINS 1 and TWINS 2 alone illustrating the advantage of stereoscopic viewing. The flux deconvolved from the TWINS images also shows spatial and temporal correlations with Time History of Events and Macroscale Interactions during Substorms (THEMIS) in situ measurements. Magnetic field dipolarizations observed by GOES support the existence of a peak in the ion flux in the midnight/dawn sector. In summary, increased spatial resolution from TWINS stereoscopic ENA images is demonstrated. Multiple peaks in the ion flux of trapped particles in the ring current are observed. THEMIS electrostatic analyzer in situ ion flux measurements and GOES geosynchronous magnetic field measurements are consistent with the spatial and temporal structure obtained.
Numerical simulation studies of the Earth's radiation belts are important to understand the acceleration and loss of energetic electrons. The Comprehensive Inner Magnetosphere‐Ionosphere (CIMI) model considers the effects of the ring current and plasmasphere on the radiation belts to obtain plausible results. The CIMI model incorporates pitch angle, energy, and cross diffusion of electrons, due to chorus and plasmaspheric hiss waves. These parameters are calculated using statistical wave distribution models of chorus and plasmaspheric hiss amplitudes. However, currently, these wave distribution models are based only on a single‐parameter, geomagnetic index (AE) and could potentially underestimate the wave amplitudes. Here we incorporate recently developed multiparameter chorus and plasmaspheric hiss wave models based on geomagnetic index and solar wind parameters. We then perform CIMI simulations for two geomagnetic storms and compare the flux enhancement of MeV electrons with data from the Van Allen Probes and Akebono satellites. We show that the relativistic electron fluxes calculated with multiparameter wave models resemble the observations more accurately than the relativistic electron fluxes calculated with single‐parameter wave models. This indicates that wave models based on a combination of geomagnetic index and solar wind parameters are more effective as inputs to radiation belt models.
A flux dropout is a sudden and sizable decrease in the energetic electron population of the outer radiation belt on the time scale of a few hours. We simulated a flux dropout of highly relativistic >2.5 MeV electrons using the Radiation Belt Environment model, incorporating the pitch angle diffusion coefficients caused by electromagnetic ion cyclotron (EMIC) waves for the geomagnetic storm event of 23–26 October 2002. This simulation showed a remarkable decrease in the >2.5 MeV electron flux during main phase of the storm, compared to those without EMIC waves. This decrease was independent of magnetopause shadowing or drift loss to the magnetopause. We suggest that the flux decrease was likely to be primarily due to pitch angle scattering to the loss cone by EMIC waves. Furthermore, the >2.5 MeV electron flux calculated with EMIC waves correspond very well with that observed from Solar Anomalous and Magnetospheric Particle EXplorer spacecraft. EMIC wave scattering is therefore likely one of the key mechanisms to understand flux dropouts. We modeled EMIC wave intensities by the Kp index. However, the calculated dropout is a several hours earlier than the observed one. We propose that Kp is not the best parameter to predict EMIC waves.
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