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A moderate geomagnetic storm (Sym/H similar to-100 nT) during June 28 and 29, 2013 was studied using Comprehensive Inner Magnetosphere-Ionosphere (CIMI) simulations and results were compared with Two wide-angle Imaging Neutral-atom Spectrometers (TWINS) observations of the spatial and temporal evolution of ring current (RC) ions including ion pressure, anisotropy, intensity, and median energy. At the onset of the storm (11:00 UT on June 28), TWINS ion pressure peaks were located radially outward and dusk ward compared to CIMI. During the main phase and the recovery phase (06:00 UT on June 28 to 16:00 UT on June 29), southward IMF Bz and rapid AE index fluctuations were observed indicating substorm ion injections and TWINS observed multiple ion pressure peaks at least one of which were found to be close to the locations of CIMI ion pressure peaks. TWINS also observed regions of parallel pressure anisotropy near pre-midnight sectors. The RC ion energies in TWINS were found to be very low (

Energy coupling between the solar wind and the Earth's magnetosphere can affect the electron population in the outer radiation belt. However, the precise role of different internal and external mechanisms that leads to changes of the relativistic electron population is not entirely known. This paper describes how ultralow frequency (ULF) wave activity during the passage of Alfvenic solar wind streams contributes to the global recovery of the relativistic electron population in the outer radiation belt. To investigate the contribution of the ULF waves, we searched the Van Allen Probes data for a period in which we can clearly distinguish the enhancement of electron fluxes from the background. We found that the global recovery that started on 22 September 2014, which coincides with the corotating interaction region preceding a high‐speed stream and the occurrence of persistent substorm activity, provides an excellent scenario to explore the contribution of ULF waves. To support our analyses, we employed ground‐ and space‐based observational data and global magnetohydrodynamic simulations and calculated the ULF wave radial diffusion coefficients employing an empirical model. Observations show a gradual increase of electron fluxes in the outer radiation belt and a concomitant enhancement of ULF activity that spreads from higher to lower L‐shells. Magnetohydrodynamic simulation results agree with observed ULF wave activity in the magnetotail, which leads to both fast and Alfven modes in the magnetospheric nightside sector. The observations agree with the empirical model and are confirmed by phase space density calculations for this global recovery period.

The LEXI and SMILE missions will provide soft X‐ray images of the Earth's magnetosheath and cusps after their anticipated launch in 2023 and 2024, respectively. The IBEX mission showed the potential of an Energetic Neutral Atom (ENA) instrument to image dayside magnetosheath and cusps, albeit over the long hours required to raster an image with a single pixel imager. Thus, it is timely to discuss the two imaging techniques and relevant science topics. We simulate soft X‐ray and low‐ENA images that might be observed by a virtual spacecraft during two interesting solar wind scenarios: a southward turning of the interplanetary magnetic field and a sudden enhancement of the solar wind dynamic pressure. We employ the OpenGGCM global magnetohydrodynamics model and a simple exospheric neutral density model for these calculations. Both the magnetosheath and the cusps generate strong soft X‐rays and ENA signals that can be used to extract the locations and motions of the bow shock and magnetopause. Magnetopause erosion corresponds closely to the enhancement of dayside reconnection rate obtained from the OpenGGCM model, indicating that images can be used to understand global‐scale magnetopause reconnection. When dayside imagers are installed with high‐ENA inner‐magnetosphere and FUV/UV aurora imagers, we can trace the solar wind energy flow from the bow shock to the magnetosphere and then to the ionosphere in a self‐standing manner without relying upon other observatories. Soft X‐ray and/or ENA imagers can also unveil the dayside exosphere density structure and its response to space weather., Key Points Soft X‐ray and Energetic Neutral Atom (ENA) imaging instruments provide an innovative way to visualize the global solar wind‐magnetosphere interactionHigh‐cadence, wide field‐of‐view soft X‐ray, and ENA images can capture the motion of the bow shock and magnetopauseThe magnetopause motion can reveal the magnetopause reconnection mode on a global scale

We present a new expansion of the Polar Wind Outflow Model (PWOM) to include kinetic ions using the Particle-in-Cell (PIC) approach with Monte Carlo collisions. This implementation uses the original hydrodynamic solution at low altitudes for efficiency, and couples to the kinetic solution at higher altitudes to account for kinetic effects important for ionospheric outflow. The modeling approach also includes wave-particle interactions, suprathermal electrons, and an hybrid parallel computing approach combining shared and distributed memory paralellization. The resulting model is thus a comprehensive, global, model of ionospheric outflow that can be run efficiently on large supercomputing clusters. We demonstrate the model’s capability to study a range of problems starting with the comparison of kinetic and hydrodynamic solutions along a single field line in the sunlit polar cap, and progressing to the altitude evolution of the ion conic distribution in the cusp region. The interplay between convection and the cusp on the global outflow solution is also examined. Finally, we demonstrate the impact of these new model features on the magnetosphere by presenting the first 2-way coupled ionospheric outflow-magnetosphere calculation including kinetic ion effects.

Energetic O+ ions (tens of keV) rapidly increase in the inner magnetosphere and contribute significantly to the ring current during substorms. Previously, two source regions of the energetic O+ ions have been proposed. The first one is the dayside polar region. Ions from the dayside polar region are transported to the lobe; then they are injected to the nightside plasma sheet during substorm expansion phase. The second one is the nightside aurora region. After the substorm onset, energetic O+ ions are extracted from the ionosphere with the auroral acceleration processes, and the O+ ions are directly supplied to the nightside plasma sheet. We investigated the relative importance of these two regions on supplying the energetic O+ ions in the inner magnetosphere. We performed a test particle simulation in global MHD electromagnetic fields. We obtained the following results. (1) During the substorm growth phase, O+ ions at tens of eV are extracted from the dayside polar region, resulting in the enhancement of the warm O+ ions (hundreds of eV) in the lobe. After the substorm onset, the warm O+ ions are nonadiabatically accelerated to tens of keV and injected to the inner magnetosphere. These O+ ions contribute to most of the O+ ring current. (2) O+ ions at less than a few keVs are supplied from the nightside aurora region to the plasma sheet. However, their contribution to the O+ ring current remains small. From the results, we concluded that the main source of the energetic O+ ions is the dayside polar region.

A scheme is suggested and tested for forecasting severe space weather (SvSW) using solar wind velocity (V) and the north-south component (Bz) of the interplanetary magnetic field (IMF) measured using the ACE (Advanced Composition Explorer) satellite from 1998 to 2016. SvSW has caused all known electric power outages and telegraph system failures. Earlier SvSW events such as the Carrington event of 1859, Quebec event of 1989 and an event in 1958 are included with information from the literature. Dst storms are used as references to identify 89 major space weather events (DstMin ≤ -100 nT) in 1998-2016. The coincidence of high CME front (or CME shock) velocity ΔV (sudden increase in V over the background by over 275 km/s) and sufficiently large Bz southward at the time of the ΔV increase is associated with SvSW; and their product (ΔV x Bz) is found to exhibit a large negative spike at the speed increase. Such a product (ΔV x Bz) exceeding a threshold seems suitable for forecasting SvSW. However, the coincidence of high V (not containing ΔV) and large Bz southward does not correspond to SvSW, indicating the importance of the impulsive action of large Bz southward and high ΔV coming through when they coincide. The need for the coincidence is verified using the CRCM (Comprehensive Ring Current Model) model, that produces extreme Dst storms (

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 events 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.

We investigate an electron flux dropout during a weak storm on 7–8 November 2008, with Dst minimum value being −37 nT. During this period, two clear dropouts were observed on GOES 11 > 2 MeV electrons. We also find a simultaneous dropout in the subrelativistic electrons recorded by Time History of Events and Macroscale Interactions during Substorms probes in the outer radiation belt. Using the Radiation Belt Environment model, we try to reproduce the observed dropout features in both relativistic and subrelativistic electrons. We found that there are local time dependences in the dropout for both observation and simulation in subrelativistic electrons: (1) particle loss begins from nightside and propagates into dayside and (2) resupply starts from near dawn magnetic local time and propagates into the dayside following electron drift direction. That resupply of the particles might be caused by substorm injections due to enhanced convection. We found a significant precipitation in hundreds keV electrons during the dropout. We observe electromagnetic ion cyclotron and chorus waves both on the ground and in space. We find the drift shells are opened near the beginning of the first dropout. The dropout in MeV electrons at GEO might therefore be initiated due to the magnetopause shadowing, and the followed dropout in hundreds keV electrons might be the result of the combination of magnetopause shadowing and precipitation loss into the Earth's atmosphere.

From 2 to 5 UT on 14 November 2012, the Van Allen Probes observed repeated particle flux dropouts during the main phase of a geomagnetic storm as the satellites traversed the post-midnight to dawnside inner magnetosphere. Each flux dropout corresponded to an abrupt change in the magnetic topology, i.e., from a more dipolar configuration to a configuration with magnetic field lines stretched in the dawn-dusk direction. Geosynchronous GOES spacecraft located in the dusk and near-midnight sectors and the LANL constellation with wide local time coverage also observed repeated flux dropouts and stretched field lines with similar occurrence patterns to those of the Van Allen Probe events. THEMIS recorded multiple transient abrupt expansions of the evening-side magnetopause ∼20–30 min prior to the sequential Van Allen Probes observations. Ground-based magnetograms and all sky images demonstrate repeatable features in conjunction with the dropouts. We combine the various in situ and ground-based measurements to define and understand the global spatiotemporal features associated with the dropouts observed by the Van Allen Probes. We discuss various proposed hypotheses for the mechanism that plausibly caused this storm-time dropout event as well as formulate a new hypothesis that explains the combined in situ and ground-based observations: the earthward motion of magnetic flux ropes containing lobe plasmas that form along an extended magnetotail reconnection line in the near-Earth plasma sheet.

To study the magnetopause on both MHD and kinetic scales, we have analyzed two Time History of Events and Macroscale Interactions during Substorms/Acceleration, Reconnection, Turbulence, and Electrodynamics of the Moon's Interaction with the Sun magnetopause crossings under steady slow-solar wind and minimum magnetic shear conditions. These events approximate a ground state of the magnetospheric boundary with minimum influences from large-solar wind disturbances and magnetic reconnection. Our observations reveal evidence for the Kelvin-Helmholtz instability, the quasi-periodicity of magnetopause surface waves accompanied by highly asymmetrical plasma signatures between the inbound (from magnetosheath to low-latitude boundary layer (LLBL)) and the outbound (from LLBL to magnetosheath) magnetopause crossings. Stronger plasma and magnetic gradients were observed during the outbound crossings but more gradual and volatile variations at higher frequencies during the inbounds. The scale lengths of the magnetic and plasma gradients were comparable or less than the proton gyroradius. Enhancements of lower hybrid waves occurred at the locations of strong gradients or variations. We interpreted the collocations of the lower hybrid waves and plasma gradients and their variations in terms of (1) lower hybrid instabilities that directly convert solar wind flow energy into lower hybrid waves and other wave modes in the LLBL, or (2) Kelvin-Helmholtz instability and magnetic reconnection which produce the conditions for the lower hybrid instabilities to grow. The rate of ion diffusion across the magnetopause caused by the lower hybrid instability is marginally sufficient to populate the LLBL. The diffusion coefficient of O+ is ~30 times larger than that of H+. The lower hybrid waves could contribute to the energy dissipation at plasma gradients in magnetopause surface wave structures and limit Kelvin-Helmholtz instability growth further downstream.

Global, ion equatorial flux distributions and energy spectra are presented from stereoscopic Two Wide-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 ≈ −70 to −80 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.

Following a long period of observation and investigation beginning in the early 1970s, it has been firmly established that Earth׳s magnetosphere is defined as much by the geogenic plasma within it as by the geomagnetic field. This plasma is not confined to the ionosphere proper, defined as the region within a few density scale heights of the F-region plasma density peak. Rather, it fills the flux tubes on which it is created, and circulates throughout the magnetosphere in a pattern driven by solar wind plasma that becomes magnetically connected to the ionosphere by reconnection through the dayside magnetopause. Under certain solar wind conditions, plasma and field energy is stored in the magnetotail rather than being smoothly recirculated back to the dayside. Its release into the downstream solar wind is produced by magnetotail disconnection of stored plasma and fields both continuously and in the form of discrete plasmoids, with associated generation of energetic Earthward-moving bursty bulk flows and injection fronts. A new generation of global circulation models is showing us that outflowing ionospheric plasmas, especially O + , load the system in a different way than the resistive F-region load of currents dissipating energy in the plasma and atmospheric neutral gas. The extended ionospheric load is reactive to the primary dissipation, forming a time-delayed feedback loop within the system. That sets up or intensifies bursty transient behaviors that would be weaker or absent if the ionosphere did not “strike back” when stimulated. Understanding this response appears to be a necessary, if not sufficient, condition for us to gain accurate predictive capability for space weather. However, full predictive understanding of outflow and incorporation into global simulations requires a clear observational and theoretical identification of the causal mechanisms of the outflows. This remains elusive and requires a dedicated mission effort.

Coronal mass ejections (CMEs) and corotating interaction regions associated with high speed solar wind streams (CIR/HSSs) drive geomagnetic storms in the terrestrial magnetosphere. Each type of storm driver yields different dynamics of storm evolution. We present results from comparative superposed epoch analyses of global ion temperatures calculated from TWINS energetic neutral atom (ENA) data and simulations using the comprehensive ring current model (CRCM). During the June 2008–April 2012 timeframe, 48 geomagnetic storms (minimum Dst≤−40 nT) occurred. Of these, 21 storms were CME-driven and 15 were driven by CIR/HSSs. Superposed epoch analysis results demonstrate that ion temperatures increase during the recovery phase of CIR/HSS-driven storms, while ions are rapidly heated at the commencement of CME-driven storms then cool over the main phase, particularly for intense (minimum Dst≤−78 nT) CME-driven storms. Higher energy ions are convected to lower L-shells during CME-driven storms, while CIR/HSS-driven storms tend to have average ion temperatures that are higher on the dayside than nightside.

On 21 January 2005, a moderate magnetic storm produced a number of anomalous features, some seen more typically during superstorms. The aim of this study is to establish the differences in the space environment from what we expect (and normally observe) for a storm of this intensity, which make it behave in some ways like a superstorm. The storm was driven by one of the fastest interplanetary coronal mass ejections in solar cycle 23, containing a piece of the dense erupting solar filament material. The momentum of the massive solar filament caused it to push its way through the flux rope as the interplanetary coronal mass ejection decelerated moving toward 1 AU creating the appearance of an eroded flux rope (see companion paper by Manchester et al. (2014)) and, in this case, limiting the intensity of the resulting geomagnetic storm. On impact, the solar filament further disrupted the partial ring current shielding in existence at the time, creating a brief superfountain in the equatorial ionosphere—an unusual occurrence for a moderate storm. Within 1 h after impact, a cold dense plasma sheet (CDPS) formed out of the filament material. As the interplanetary magnetic field (IMF) rotated from obliquely to more purely northward, the magnetotail transformed from an open to a closed configuration and the CDPS evolved from warmer to cooler temperatures. Plasma sheet densities reached tens per cubic centimeter along the flanks—high enough to inflate the magnetotail in the simulation under northward IMF conditions despite the cool temperatures. Observational evidence for this stretching was provided by a corresponding expansion and intensification of both the auroral oval and ring current precipitation zones linked to magnetotail stretching by field line curvature scattering. Strong Joule heating in the cusps, a by-product of the CDPS formation process, contributed to an equatorward neutral wind surge that reached low latitudes within 1–2 h and intensified the equatorial ionization anomaly. Understanding the geospace consequences of extremes in density and pressure is important because some of the largest and most damaging space weather events ever observed contained similar intervals of dense solar material.

We have integrated dynamic, spatiotemporally resolved ion temperature boundary conditions into the Comprehensive Ring Current Model (CRCM), which are based on 2-D equatorial maps derived from the Two Wide-Angle Imaging Neutral-Atom Spectrometers (TWINS) energetic neutral atom (ENA) data. The high-speed stream-driven event on 22 July 2009 is simulated and compared against an identical simulation using a statistically derived boundary condition model. ENA-derived temperatures allow users to include event-specific observations associated with a dynamic plasma sheet. This method also provides temperatures in the important region between geosynchronous orbit and the plasma sheet, a region which existing empirical models exclude. We find that the spatial and energy distributions of ring current flux and pressure have sensitive dependence on boundary conditions during this event. The coupling of boundary conditions to the time history of the convection field strength also plays an important role by throttling the influence of the boundary plasma on the inner magnetosphere. Simulated moments and spectra from our simulations are compared with remotely imaged ion temperatures from TWINS and also in situ energy spectra and temperature moments from Time History of Events and Macroscale Interactions during Substorms-D. Storm time dusk-dawn asymmetries consistent with observational data, such as Zhang et al. (2006), are reproduced well when CRCM is provided with the event-specific boundary model. A hot localized structure observed by TWINS at geosynchronous midnight during a strong northward interplanetary magnetic field interval is also reproduced with this boundary model, whereas the empirical boundary model fails to yield this feature.

We have developed a technique for estimating the temporal evolution of the plasmaspheric helium ion density based on a sequence of extreme ultraviolet (EUV) data obtained from the IMAGE satellite. In the proposed technique, the estimation is obtained by incorporating EUV images from IMAGE into a two-dimensional fluid model of the plasmasphere using a data assimilation approach based on the ensemble transform Kalman filter. Since the motion and the spatial structure of the helium plasmasphere is strongly controlled by the electric field in the inner magnetosphere, the electric field around the plasmapause can also be estimated using the ensemble transform Kalman filter. We performed an experiment using synthetic images that were generated from the same numerical model under a certain condition. It was confirmed that the condition that generated the synthetic images was successfully reproduced. We also present some results obtained using real EUV imaging data. Finally, we discuss the possibility of estimating the density profile along a magnetic field line. Since each EUV image was taken from a different direction due to the motion of the IMAGE satellite, we could obtain the information on the density profile along a field line by combining multiple images.

During large geomagnetic storms (Dst ≤−100 nT), oxygen can become a significant component of the energetic particles of the inner magnetosphere. Until recently, there were no available global observations of the medium energy ( 52 keV) O ENAs.

[1] We have recently extended the global magnetohydrodynamic (MHD) model BATS-R-US to account for pressure anisotropy. Since the inner magnetosphere dynamics cannot be fully described even by anisotropic MHD, we coupled our anisotropic MHD model with two inner magnetospheric models: the Rice Convection Model (RCM) and the Comprehensive Ring Current Model (CRCM). The coupled models provide better representations of the near-Earth plasma, especially during geomagnetic storms. In this paper, we present the two-way coupling algorithms with both ring current models. The major difference between these two couplings is that the RCM assumes isotropic and constant pressures along closed field lines, while the CRCM resolves pitch angle anisotropy. For model validation, we report global magnetosphere simulations performed by the coupled models. The simulation results are compared to the results given by the coupled isotropic MHD and ring current models. We find that in the global MHD simulations coupled with ring current models, pressure anisotropy results in a thinner magnetosheath, a shorter tail, a much smaller Earthward plasma jet from the tail reconnection site, and is also important in controlling the magnetic field configuration. The comparisons with satellite data for the magnetospheric event simulations show improvements on reproducing the measured tail magnetic field and inner magnetospheric flow velocity when including pressure anisotropy in the ring current model coupled global MHD model.

[1] We present the coupling methodology and validation of a fully coupled inner and global magnetosphere code using the infrastructure provided by the Space Weather Modeling Framework (SWMF). In this model, the Comprehensive Ring Current Model (CRCM) represents the inner magnetosphere, while the Block‒Adaptive‒Tree Solar‒Wind Roe‒Type Upwind Scheme (BATS‒R‒US) represents the global magnetosphere. The combined model is a global magnetospheric code with a realistic ring current and consistent electric and magnetic fields. The computational performance of the model was improved to surpass real‒time execution by the use of the Message Passing Interface (MPI) to parallelize the CRCM. Initial simulations under steady driving found that the coupled model resulted in a higher pressure in the inner magnetosphere and an inflated closed field‒line region as compared to simulations without inner‒magnetosphere coupling. Our validation effort was split into two studies. The first study examined the ability of the model to reproduce Dst for a range of events from the Geospace Environment Modeling (GEM) Dst Challenge. It also investigated the possibility of a baseline shift and compared two approaches to calculating Dst from the model. We found that the model did a reasonable job predicting Dst and Sym‒H according to our two metrics of prediction efficiency and predicted yield. The second study focused on the specific case of the 22 July 2009 moderate geomagnetic storm. In this study, we directly compare model predictions and observations for Dst, THEMIS energy spectragrams, TWINS ENA images, and GOES 11 and 12 magnetometer data. The model did an adequate job reproducing trends in the data. Moreover, we found that composition can have a large effect on the result.

[1] The storm-time magnetic disturbance at the Earth's equator, as commonly measured by the Dst index, is induced by currents in the near-Earth magnetosphere. The ring current is generally considered the most important contributor, but other magnetospheric currents have also been found to have significant effects. Of the two main types of solar geomagnetic storm drivers, Coronal Mass Ejections (CMEs) tend to have a much greater impact on Dst than Corotating Interaction Regions (CIRs). Ring current models have been found to underestimate Dst, particularly during storms driven by CIRs. One possible explanation is that the models neglect to handle some aspect of ring current physics that is particularly important for CIRs. This study uses the Comprehensive Ring Current Model (CRCM) to estimate the ring current contribution to Dst for a selection of storms of various strengths and different drivers (CMEs and CIRs) that have solar wind parameters that fit a typical profile. The model boundary is set to 10 RE at the equator, encompassing the entire ring current region. The magnetic field is held fixed, based on average storm parameters, which limits our model results to the effects of convection and plasma sheet density at the model boundary. Our model results generally show good agreement with the size and timing of fluctuations in Dst, which indicates that convection and boundary conditions play an important role in shaping Dst. We also find excellent agreement with the magnitude of Dst for CME-driven storms. For CIR-driven storms, however, the magnitude at the peak of the storm frequently deviates from actual Dst. In general, we agree with the results of previous research that CIR-driven storms are more underpredicted. However, this study includes some weaker CIR-driven storms for which Dst is actually overpredicted. Overall, when examining the dependence of modeled Dst* on actual Dst* at storm peak, we find that there is a statistically significant difference between CME- and CIR-driven storms. We also find that approximately half of the total ring current energy lies beyond an L-value of 6.6. However, this figure could be overestimated due to the use of a static magnetic field, which limits radial transport.

The fluxes of energetic particles in the radiation belts are found to be strongly controlled by the solar wind conditions. In order to understand and predict the radiation particle intensities, we have developed a physics-based Radiation Belt Environment (RBE) model that considers the influences from the solar wind, ring current and plasmasphere. Recently, an improved calculation of wave-particle interactions has been incorporated. In particular, the model now includes cross diffusion in energy and pitch-angle. We find that the exclusion of cross diffusion could cause significant overestimation of electron flux enhancement during storm recovery. The RBE model is also connected to MHD fields so that the response of the radiation belts to fast variations in the global magnetosphere can be studied. We are able to reproduce the rapid flux increase during a substorm dipolarization on 4 September 2008. The timing is much shorter than the time scale of wave associated acceleration. Published by Elsevier Ltd.

Because of the small planetary magnetic field as well as proximity to the Sun that leads to enhanced solar wind pressure as compared to Earth, the magnetosphere of Mercury is very dynamical and at times subjected to prominent compression. We investigate the dynamics of magnetospheric ions during such compression events. Using three-dimensional single-particle simulations, we show that the electric field induced by the time varying magnetic field can lead to significant ion energization, up to several hundreds of eVs or a few keVs. This energization occurs in a nonadiabatic manner, being characterized by large enhancements of the ion magnetic moment and bunching in gyration phase. It is obtained when the ion cyclotron period is comparable to the field variation time scale. This condition for nonadiabatic heating is realized in distinct regions of space for ions with different mass-to-charge ratios. During compression of Mercury's magnetosphere, heavy ions originating from the planetary exosphere may be subjected to such an abrupt energization, leading to loading of the magnetospheric lobes with energetic material.

We have integrated the Fok radiation belt environment (RBE) model into the space weather modeling framework (SWMF). RBE is coupled to the global magnetohydrodynamics component (represented by the Block-Adaptive-Tree Solar-wind Roe-type Upwind Scheme, BATS-R-US, code) and the Ionosphere Electrodynamics component of the SWMF, following initial results using the Weimer empirical model for the ionospheric potential. The radiation belt (RB) model solves the convection-diffusion equation of the plasma in the energy range of 10 keV to a few MeV. In stand-alone mode RBE uses Tsyganenko's empirical models for the magnetic field, and Weimer's empirical model for the ionospheric potential. In the SWMF the BATS-R-US model provides the time dependent magnetic field by efficiently tracing the closed magnetic field-lines and passing the geometrical and field strength information to RBE at a regular cadence. The ionosphere electrodynamics component uses a two-dimensional vertical potential solver to provide new potential maps to the RBE model at regular intervals. We discuss the coupling algorithm and show some preliminary results with the coupled code. We run our newly coupled model for periods of steady solar wind conditions and compare our results to the RB model using an empirical magnetic field and potential model. We also simulate the RB for an active time period and find that there are substantial differences in the RB model results when changing either the magnetic field or the electric field, including the creation of an outer belt enhancement via rapid inward transport on the time scale of tens of minutes.

We investigate the dynamics of magnetospheric ions during transient reconfigurations of Mercury's magnetotail. At Earth, numerous observations during similar events reveal a prominent energization (up to the hundreds of keV range) of heavy ions ( O + ) originating from the topside ionosphere. This energization likely results from a resonant nonadiabatic interaction with the electric field that is induced by dipolarization of the magnetic field lines, the time scale of this reconfiguration being comparable to the heavy ion cyclotron period. The question then arises whether such an energization may occur at Mercury. Using single-particle simulations in time-varying electric and magnetic fields, we show that prominent nonadiabatic heating is obtained for ions with small mass-to-charge ratios (e.g., H + , He + ). As for heavy ions (e.g., Na + , Ca + ) that have cyclotron periods well above the time scale of the magnetotail reconfiguration (several seconds), a weaker energization is obtained. The resonant heating mechanism that we examine here may be of importance for solar wind protons that gain access to the inner hermean magnetotail as well as for light ions of planetary origin that directly feed the near-Mercury plasma sheet.

We investigate the dynamics of charged particles in the dayside magnetosphere in response to abrupt variations of the solar wind dynamical pressure. Using test particle simulations, we show that the electric field induced by the compression of the frontside magnetosphere may be responsible for prominent energization of plasma sheet ions as well as trapping at high latitudes. We demonstrate that, due to the short-lived character of the magnetic field line reconfiguration (on the time scale of a few minutes), the particle magnetic moment (first adiabatic invariant) may not be conserved during such events. Ions that are initially bouncing from one hemisphere to the other are found to experience nonadiabatic energization up to the hundred of keV range while being injected into the outer cusp. Such injections involve particles from limited portions of the dayside flux tubes. The energetic particles that are produced in the outer cusp during such events subsequently circulate about the field minimum at high latitudes without intercepting the equatorial plane, thus contributing to the high-energy populations that are observed in this region of space.

We report observations of neutral atoms from the solar wind in the Earth's vicinity with the low-energy neutral atom (LENA) imager on the Imager for Magnetopause-to-Aurora Global Exploration (IMAGE) spacecraft. This instrument was designed to be capable of looking at and in the direction of the Sun. Enhancements in the hydrogen count rate in the solar direction are not correlated with either solar ultraviolet emission or suprathermal ions and are deduced to be due to neutral particles from the solar wind. LENA observes these particles from the direction closest to that of the Sun even when the Sun is not directly in LENA's 90° field of view. Simulations show that these neutrals are the result of solar wind ions charge exchanging with exospheric neutral hydrogen atoms in the postshock flow of the solar wind in the magnetosheath. Their energy is inferred to exceed 300 eV, consistent with solar wind energies, based on simulation results and on the observation of oxygen ions, sputtered from the conversion surface in the time-of-flight spectra. In addition, the sputtered oxygen abundance tracks the solar wind speed, even when IMAGE is deep inside the magnetosphere. These results show that low-energy neutral atom imaging provides the capability to directly monitor the solar wind flow in the magnetosheath from inside the magnetosphere because there is a continuous and significant flux of neutral atoms originating from the solar wind that permeates the magnetosphere.

The discovery of terrestrial O+ and other heavy ions in magnetospheric hot plasmas, combined with the association of energetic ionospheric outflows with geomagnetic activity, led to the conclusion that increasing geomagnetic activity is responsible for filling the magnetosphere with ionospheric plasma. Recently it has been discovered that a major source of ionospheric heavy ion plasma outflow is responsive to the earliest impact of coronal mass ejecta upon the dayside ionosphere. Thus a large increase in ionospheric outflows begins promptly during the initial phase of geomagnetic storms, and is already present during the main phase development of such storms. We hypothesize that enhancement of the internal source of plasma actually supports the transition from substorm enhancements of aurora to storm-time ring current development in the inner magnetosphere. Other planets known to have ring current-like plasmas also have substantial internal sources of plasma, notably Jupiter and Saturn. One planet having a small magnetosphere, but very little internal source of plasma, is Mercury. Observations suggest that Mercury has substorms, but are ambiguous with regard to the possibility of magnetic storms of the planet. The Messenger mission to Mercury should provide an interesting test of our hypothesis. Mercury should support at most a modest ring current if its internal plasma source is as small as is currently believed. If substantiated, this hypothesis would support a general conclusion that the magnetospheric inflationary response is a characteristic of magnetospheres with substantial internal plasma sources. We quantitatively define this hypothesis and pose it as a problem in comparative magnetospheres.

On May 13, 1996, as the Polar spacecraft was traveling at high invariant latitudes (∼78°–79°) in the prenoon sector (∼1050 magnetic local time), the Thermal Ion Dynamics Experiment on board recorded successive injections of protons with clear energy-time dispersion. These dispersion structures spread over several minutes and extend from several hundreds of eV down to a few tens of eV. During this pass, simultaneous measurements from the Wind spacecraft revealed little variation of the solar wind dynamical pressure but a gradual turning of the interplanetary magnetic field (IMF) from an essentially dawn-to-dusk orientation (i.e., predominant positive BY component and slightly negative BZ) to a north-to-south one (predominant negative BZ). We show that the observed injections result from magnetosheath particle entry at higher and higher latitudes in the dawn sector. Using test particle calculations in a simple model of reconnected interplanetary and magnetospheric field, we show that the injection modulation likely follows from changes in the dynamical regime experienced by the ions upon traversal of the magnetopause current sheet. That is, as the IMF gradually rotates, the time-varying BY and BZ lead to changes in the adiabaticity parameter κ in the region of entry and affect particle access to the Polar location. In the morning sector where magnetosheath plasma accelerates downtail, such an access to the inner magnetosphere requires magnetic moment damping and is thus favored during nonadiabatic episodes. The flux variations obtained numerically are in qualitative agreement with those observed, both in terms of characteristic energy and overall time evolution. This supports our interpretation of the modulated ion injections in terms of intermittent nonadiabatic entry from the magnetosheath followed by time of flight dispersion between the magnetopause and the spacecraft.

The ring current during a geomagnetic storm on May 2, 1986 has been modeled using a bounce averaged kinetic equations for the phase space density of hydrogen ions, considering charge exchange and Coulomb losses along the drift path. The resulting equatorial pitch angle distribution is used to generate data simulating the medium and high energy neutral atom imagers to be flown on IMAGE. A method for deconvolving these images is described and applied to the simulated data. The results show that, when there are sufficient counts, the deconvolved distribution contains the main features of the original source and that the energy spectrum at a specific time as well as the total energy of the ring current as a function of time can be extracted from the energetic neutral atom images.