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Recent attention has been given to mesoscale phenomena across geospace (∼10 s km to 500 km in the ionosphere or ∼0.5 RE to several RE in the magnetosphere), as their contributions to the system global response are important yet remain uncharacterized mostly due to limitations in data resolution and coverage as well as in computational power. As data and models improve, it becomes increasingly valuable to advance understanding of the role of mesoscale phenomena contributions—specifically, in magnetosphere-ionosphere coupling. This paper describes a new method that utilizes the 2D array of Time History of Events and Macroscale Interactions during Substorms (THEMIS) white-light all-sky-imagers (ASI), in conjunction with meridian scanning photometers, to estimate the auroral scale sizes of intense precipitating energy fluxes and the associated Hall conductances. As an example of the technique, we investigated the role of precipitated energy flux and average energy on mesoscales as contrasted to large-scales for two back-to-back substorms, finding that mesoscale aurora contributes up to ∼80% (∼60%) of the total energy flux immediately after onset during the early expansion phase of the first (second) substorm, and continues to contribute ∼30–55% throughout the remainder of the substorm. The average energy estimated from the ASI mosaic field of view also peaked during the initial expansion phase. Using the measured energy flux and tables produced from the Boltzmann Three Constituent (B3C) auroral transport code (Strickland et al., 1976; 1993), we also estimated the 2D Hall conductance and compared it to Poker Flat Incoherent Scatter Radar conductance values, finding good agreement for both discrete and diffuse aurora.

Effects of scattering of electrons from whistler chorus waves and of ions due to field line curvature on diffuse precipitating particle fluxes and ionospheric conductance during the large 17 March 2013 storm are examined using the self-consistent Rice Convection Model Equilibrium (RCM-E) model. Electrons are found to dominate the diffuse precipitating particle integrated energy flux, with large fluxes from ~21:00 magnetic local time (MLT) eastward to ~11:00 MLT during the storm main phase. Simulated proton and oxygen ion precipitation due to field line curvature scattering is sporadic and localized, occurring where model magnetic field lines are significantly stretched on the night side at equatorial geocentric radial distances r(0) ≳8 R(E) and/or at r(0) ~5.5 to 6.5 R(E) from dusk to midnight where the partial ring current field has perturbed the magnetic field. The precipitating protons likewise contribute sporadically to the storm time Hall and Pedersen conductance in localized regions whereas the precipitating electrons are the dominate storm time contributor to enhanced Hall and Pedersen conductance at auroral magnetic latitudes on the night and morning side. The RCM-E model can reproduce general features of the Van Allen Probe/MagEIS observed trapped electron differential flux spectrograms over energies of ~37 to 150 keV. The simulations with a parameterized electron loss model also reproduce reasonably well the storm time Defense Meteorological Satellite Program integrated electron energy flux at 850 km at satellite crossings from predawn to midmorning. However, model-data agreement is not as good from dusk to premidnight where there are large uncertainties in the electron loss model.

During geomagnetic storms and substorms, the magnetosphere and ionosphere are strongly coupled by precipitating magnetospheric electrons from the Earth's plasma sheet and driven by both magnetospheric and ionospheric processes. Magnetospheric wave activity initiates electron precipitation, and the ionosphere and upper atmosphere further facilitate this process by enhancing the value of precipitated energy uxes via connection of two magnetically conjugate regions and multiple atmospheric reections. This paper focuses on the resulting electron energy uxes and afliated heightintegrated Pedersen and Hall conductances in the auroral regions produced by multiple atmospheric reections during the 17 March 2013 geomagnetic storm and their effects on the inner magnetospheric electric eld and ring current. Our study is based on the magnetically and electrically selfconsistent Rice ConvectionModelEquilibrium of the inner magnetosphere with SuperThermal Electron Transport modied electron energy uxes that take into account the electron energy interplay between the two magnetically conjugate ionospheres. SuperThermal Electron Transportmodied energy ux in the Rice ConvectionModelEquilibrium leads to a signicant difference in the global conductance pattern, ionospheric electric eld formation, Birkeland current structure, ring current energization and its energy content, subauroral polarization drifts intensications and their spatial locations, interchange instability redistribution, and overall energy interplay on the global scale.

Earth’s Magnetosphere-Ionosphere-Thermosphere system is inseparably coupled, with driving from above and below by various terrestrial and space weather phenomena. Global models have done well at capturing large-scale effects, but currently do not capture the meso-scale (~10s-500 km) phenomena which often are locally more intense. As computing power improves, and modeling meso-scales now becomes possible, it is vital to provide data-informed inputs of the relevant drivers. In this presentation, we focus on the energy flux deposited into the ionosphere from the magnetosphere by precipitating particles that result in the aurora, specifically at meso-scales, and the resulting conductance. Thanks to NASA’s THEMIS mission, an array of all-sky-imagers (ASIs) across Canada monitors the majority of the nightside auroral oval at a 3 second cadence, providing a global view at temporal & spatial resolutions required to study the aurora on meso-scales. Thus, we present 2-D maps over time of the energy flux, energy, and conductance that result from the aurora during solar storms and substorms, including those features at meso-scales. We determine conductance using the ASI-determined eflux and energy as inputs to the Boltzman Three Constituent (B3C) auroral transport code, compare values with Poker Flat ISR observations, and find a good comparison. We find that meso-scale aurora contributes at least 60-70% of the total precipitated energy flux during the first ten minutes of a substorm. Our results can be utilized by the broad community, for example, as inputs to atmospheric models or as the resulting conductance from precipitation inferred by magnetospheric models or satellite observations.

This chapter describes the properties of ring current source populations as well as transport processes that lead to ring current formation. During geomagnetic activity, the ring current intensity is highly sensitive to variations in the plasma source populations and to the processes that transport the plasma to form the ring current. The major source of electrons and ions to the ring current is the plasma sheet. In the plasma sheet, ions such as H+, O+, He+, and N+ that originate from the solar wind and/or the ionosphere comingle, and their spectral distributions vary with solar and magnetic activity. The bulk properties of plasma sheet particles have been analyzed from several observational studies and a few empirical models of bulk plasma sheet properties have been developed. The charged particles from the plasma sheet gyrate, bounce, and drift within the dynamic inner magnetospheric electric and magnetic fields. Although the particle and fields system is electrodynamic, charged particles of different energies (∼1 keV to several hundreds of keV) respond differently to electric and magnetic field variations on slower (∼ 30 min to several hours) and more rapid (∼1 to 10’s min) time scales. The concepts of convective and diffusive transport with regard to ring current formation are described. Field variations can be localized and transient, particularly during substorms, and may lead to localized and bursty injection of particles in the inner plasma sheet to the inner magnetosphere. Such transport processes and their effects on the formation of the ring current are described.

The largest variations in the plasma and fields that comprise the inner regions of the Earth’s space environment, or the magnetosphere, occur during geomagnetic storms and are related to the intensification of the ring current, the magnetically trapped charged particles that partially or fully encircle the Earth inside of ∼7 Earth radii. This chapter provides a historical introduction to the ring current and geomagnetic storms that have been investigated for more than 100 years. An overview of the relationship of the ring current to solar wind drivers and the development and decay of the ring current, in terms of the Sun-Earth connection is presented. Major space weather effects triggered by geomagnetic storms are briefly summarized. These effects intensify during extreme events, like the largest recorded geomagnetic storm that occurred in September 1859, known as the Carrington Event. Less severe storms have occurred since then, still causing many disruptions.

The long-term galactic cosmic ray (GCR) environment response of the dosimeter and surface-charging monitors on two high-altitude satellites called F1 and F2 is analyzed. These satellites also host the National Aeronautics and Space Administration’s Two Wide-angle Imaging Neutral-atom Spectrometers. The trend of the GCR intensity with solar cycle from year 2006 through 2012 is estimated from in-situ Advanced Composition Explorer (ACE) and Ulysses data. The dosimeter average 25–45 MeV proton counts and the >2.4 MeV electron counts at apogee follow the expected GCR solar-cycle trend, but the best-fit variations are smaller than estimated from ACE heavy ion GCR data. The surface-charging monitor average minima ion counts at apogee on F1, one of the host spacecraft, are consistent with the solar-cycle variation of Ulysses proton GCR counts. Linear fits to the F1 surface-charging monitor response to the GCR environment that may be subtracted from the measured counts before conversion to particle fluxes are pro...

We investigate the effects of different ionospheric conductance and electron loss models on ring current dynamics during the large magnetic storm of 5–7 April 2010 using the magnetically and electrically self-consistent Rice Convection Model–Equilibrium (RCM-E). The time-varying RCM-E proton distribution boundary conditions are specified using a combination of TWINS 1 and 2 ion temperature maps and in situ THEMIS and GOES spectral measurements in the plasma sheet. With strong electron pitch-angle diffusion, the simulated equatorial ring current electron pressure is weak with (1) uniform conductance or (2) conductance based on parameters from the International Reference Ionosphere 2007 and the feedback of simulated precipitating electrons. With the Chen and Schulz electron loss model that includes strong diffusion in the plasma sheet and weak diffusion in the plasmasphere, the stormtime equatorial RCM-E electron pressure is enhanced in the inner magnetosphere from midnight through dawn to the dayside. The enhancement extends to lower geocentric distance with uniform conductance than with the more realistic ionospheric conductance model due to electric field shielding effects. Electron losses affect not only the simulated electron pressures, but through magnetospheric-ionospheric coupling, the redistributed electric and magnetic fields affect the ring current proton transport. The simulations reproduced features observed by in situ magnetic field and proton flux data, and TWINS global ENA observations. The simulated stormtime ring current energization can vary significantly depending on the ionospheric conductance and electron loss model used. Thus, it is important to incorporate realistic descriptions of ionospheric conductance and electron losses in inner magnetospheric models.

Ions in the plasma sheet are measured by the energetic neutral atom imagers on the Two Wide-Angle Imaging Neutral-Atom Spectrometers (TWINS) spacecraft. A line of sight (LOS) projection is used to determine the location of the ions that dominate the measured spectrum, assuming that the equatorial plane is the hottest region along the LOS. We verify reasonable agreement between ion spectral shapes measured using this remote measurement technique and in situ measurements from the Time History of Events and Macroscale Interactions during Substorms (THEMIS) spacecraft during two moderate geomagnetic storms. Conditions for reliable use of this technique to determine ion spectra and effective ion temperatures are identified. The technique is applied to the substorm interval associated with the loss of communication with the Galaxy-15 satellite. During this interval, localized and broad regions of ion energization are observed, demonstrating that magnetic reconnection and current disruption may have played a role during this very extreme event. These observations demonstrate the ability of this technique to cast local ion spectra measurements in a global context.

We describe an empirical model of energetic ion plasma (∼20-400 keV/q) that is constructed from measurements taken by the Magnetospheric Ion Composition Spectrometer (MICS) instrument that flew on the CRRES spacecraft. This is a unique data set in that it provides energetic ion composition in the near-equatorial ring current region during a very active solar maximum. The model database is binned by energy, equatorial pitch angle, L shell, and magnetic local time, and provides unidirectional, differential number fluxes of the major ionic constituents of the inner magnetosphere, such as protons (H+), singly-charged oxygen (O+), and singly-charged helium (He+). The H+ and O+ model fluxes are examined in detail and are consistent with well-known particle transport effects (e.g., adiabatic heating). We also validate these model fluxes against a number of other ion plasma models that are available in the literature. The primary finding is the elevated levels of energetic O+ flux during the CRRES era. We attribute this to a solar cycle effect, related to the enhanced upwelling and oxygen outflow from the ionosphere that occurs during solar maximum, driven by elevated solar extreme ultraviolet radiation. We briefly discuss the implications that the enhanced O+ environment during the CRRES era may have for other results derived from CRRES observations (e.g., statistical wave distributions).

The equation of a magnetic field line (labeled L ) in Dungey's model magnetosphere (dipole field plus uniform southward Δ B ) is r = La [1+( r 3 /2 b 3 )]sin 2 θ , where r denotes geocentric distance, θ denotes magnetic colatitude, a is the Earth's radius, and b is the radius of the field model's equatorial neutral line. This model can be generalized (e.g., to accommodate a ring current) by treating b as a function of L and ϕ (magnetic local time) rather than as a constant, so as to yield measured or calculated values of the equatorial magnetic field B 0 . (In this generalization the equatorial neutral line has a radius b *( ϕ )=(3 a /2) L *( ϕ ) for some particular ϕ -dependent value of L called L *.) This approach yields an estimate for how a specified distortion of equatorial B 0 might map to higher latitudes. It also allows for analytical calculation of the current density J =( c /4 π ) ∇× B at arbitrary latitude. Since charged particles (of scalar momentum p ) scattered strongly in pitch angle satisfy an adiabatic invariant Λ = p 3 Ψ , where Ψ is the flux-tube volume (per unit magnetic flux), it is of interest to approximate (as well as possible) the flux-tube volume Ψ as a function of L and ϕ . By generalizing the calculation of Schulz [1998a. Particle drift and loss rates under strong pitch angle diffusion in Dungey's model magnetosphere. Journal of Geophysical Research 103, 61–67], we have found such an analytical approximation of Ψ for arbitrarily non-constant b and are using it in bounce-averaged transport simulations of diffuse auroral electrons described by a Hamiltonian function in which the kinetic energy is given by [( Λ / Ψ ) 2/3 c 2 +( m 0 c 2 ) 2 ] 1/2 − m 0 c 2 , where m 0 is the rest mass and c is the speed of light.

The ability to accurately model precipitating electron distributions is crucial for understanding magnetosphere-ionosphere-thermosphere coupling processes. We use the magnetically and electrically self-consistent Rice Convection Model-Equilibrium (RCM-E) of the inner magnetosphere to assess how well different electron loss models can account for observed electron fluxes during the large 10 August 2000 magnetic storm. The strong pitch angle scattering rate produces excessive loss on the morning and dayside at geosynchronous orbit (GEO) compared to what is observed by a Los Alamos National Laboratory satellite. RCM-E simulations with parameterized scattering due to whistler chorus outside the plasmasphere and hiss inside the plasmasphere are able to account simultaneously for trapped electron fluxes at 1.2 keV to ~100 keV observed at GEO and for precipitating electron fluxes and electron characteristic energies in the ionosphere at 833 km measured by the NOAA 15 satellite.

To investigate the spatial and spectral structure of the diffuse aurora during a model geomagnetic storm characterized by random impulses in the cross-magnetospheric convection electric field, we simulate the bounce-averaged drift motion and precipitation of plasma sheet electrons. Bounce-averaged drift trajectories are computed from a Hamiltonian formulation in which we have treated the plasma sheet electrons as though they were undergoing strong pitch angle diffusion in Dungey's model magnetosphere (dipole field plus uniform southward Bz). Using the simulation results, we map phase space densities from near the nightside neutral line according to Liouville's theorem, modified to account for particle losses consistent with the postulated pitch angle scattering. We consider three different idealized scattering rate models for the plasma sheet electrons: (1) strong diffusion everywhere, (2) an MLT-independent model for diffusion that is less than everywhere strong, and (3) an MLT-dependent scattering rate model with the same azimuthal average as the MLT-independent model. We evaluate the precipitating energy flux and mean energy at ionospheric altitude h = 127.4 km, as well as the ionospheric Hall and Pedersen conductances, for the three different scattering rate models considered, and we compare the results with each other and with available observations. The limit of everywhere strong pitch angle diffusion yields a simulated diffuse aurora that seems too intense at its maximum (storm time energy flux of ∼5–10 erg cm−2 s−1) and seems too concentrated near midnight in magnetic local time (MLT). The distribution of energy flux above half maximum extends from ∼2000–0700 MLT throughout the model storm. Corresponding maxima in simulated Hall (∼18–34 mhos) and Pedersen (∼9–11 mhos) conductances also seem too large. Our model for pitch angle diffusion that is less than everywhere strong yields a more realistic maximum energy flux (∼2 erg cm−2 s−1) and yields a realistically broader distribution in MLT, essentially because the plasma sheet electrons of interest live longer before precipitating. An even more realistic MLT distribution of precipitating energy flux is obtained by modulating the latter scattering rate model with an MLT dependence based on the observed statistical distribution of waves with respect to MLT. With such a model we can account for intensifications of diffuse auroral electron precipitation found near dawn and late in the morning quadrant in both statistical and storm event studies.

In order to understand the characteristics of the quiet time inner plasma sheet protons, we use a modified version of the Magnetospheric Specification Model to simulate the bounce averaged electric and magnetic drift of isotropic plasma sheet protons in an approximately self-consistent magnetic field. Proton differential fluxes are assigned to the model boundary to mimic a mixed tail source consisting of hot plasma from the distant tail and cooler plasma from the low latitude boundary layer (LLBL). The source is local time dependent and is based on Geotail observations and the results of the finite tail width convection model. For the purpose of self-consistently simulating plasma motion and a magnetic field, the Tsyganenko 96 magnetic field model is incorporated with additional adjustable ring-current shaped current loops. We obtain equatorial proton flow and midnight and equatorial profiles of proton pressure, number density, and temperature. We find that our results agree well with observations. This indicates that the drift motion dominates the plasma transport in the quiet time inner plasma sheet. Our simulations show that cold plasma from the LLBL enhances the number density and the proton pressure in the inner plasma sheet and decreases the dawn-dusk asymmetry of the equatorial proton pressure. From our approximately force-balanced simulations the magnetic field responds to the increase of pressure gradient force in the inner plasma sheet by changing its configuration to give a stronger magnetic force. At the same time, the plasma dynamics is affected by the changing field configuration and its associated pressure gradient force becomes smaller. Our model predicts a quiet time magnetic field configuration with a local depression in the equatorial magnetic field strength at the inner edge of the plasma sheet and a cross-tail current separated from the ring current, results that are supported by observations. A scale analysis of our results shows that in the inner plasma sheet the magnitude of the Hall term in the generalized Ohm's law is not small compared with the quiet time electric field. This suggests that the frozen-in condition E = −v×B is not valid in the inner plasma sheet and that the Hall term needs to be included to obtain an appropriate approximation of the generalized Ohm's law in that region.

Using a guiding-center simulation of plasmasheet electrons postulated to be in strong pitch angle diffusion, we compute drift trajectories from a Hamiltonian formulation and map phase space densities from the nightside neutral line in Dungey's model magnetosphere (dipole field plus uniform southward Bz) according to Liouville's theorem modified for exponential loss implicit in the strong diffusion hypothesis. From the resulting phase space distributions we compute the precipitating energy flux into the auroral ionosphere as functions of magnetic latitude and magnetic local time (MLT) so as to simulate numerically the spatial and spectral structure of diffuse auroral electron precipitation for comparison with observational data. Storm-associated impulses (by which we enhance the convection electric field) can typically transport plasmasheet electrons from the nightside neutral line to the near-midnight region of maximum precipitating energy flux (latitude ≈ 65°) in ∼20–30 min, which is roughly the strong diffusion lifetime of 4-keV electrons at the corresponding L value (≈5.7). The maximum precipitating electron energy flux in our simulation of the model storm is thus modulated by random variations in the mean cross-magnetospheric electric potential drop over the 20–30 min before the time of interest. Our results also show a consistent lack of precipitating electron energy flux in the afternoon quadrant, essentially because this is the last quadrant to be visited by plasmasheet electrons (and therefore features the most strongly attenuated phase space densities) as they drift through the magnetosphere on open trajectories. The result agrees qualitatively with the typically observed “darkness” of X-ray images of the diffuse aurora in that sector (1200–1800 MLT). While our simulation results locate the region of maximum energy flux slightly postmidnight during both prestorm and stormtime, in good agreement with previously published statistical compilations of auroral electron precipitation. Our simulations do not explain other large intensifications of electron precipitation (near dawn and in the morning sector) that are also found in both statistical and storm event studies. This suggests the need for a model in which pitch angle diffusion is less than everywhere strong throughout the plasma sheet.

Intense magnetic storms often develop in two stages such that a second ring current enhancement begins before the first ring current enhancement has recovered to the prestorm level. Since Dst traces of such storms exhibit two dips, we refer to these as double-dip storms. Here we compare double- and single-dip storms with similar convective and diffusive transport characteristics for effectiveness at forming the proton ring current. Our model storms consist of superposition of almost randomly occurring impulses in the convection electric field. We have synthesized a hypothetical double-dip storm consisting of a moderate 6-hour storm, followed by a 3-hour quiet interval and then by a more intense 15-hour storm, for a total duration of 24 hours. For comparison, we consider a single-dip model storm with an unmodulated 24-hour main phase during which the root-mean-square enhancement of the cross-tail potential drop is made equal to the timeweighted rms enhancement for the double-dip model storm. This leads to comparable timeaveraged diffusion coefficients for our single- and double-dip model storms. The mean enhancement of the cross-tail potential drop of the two storms are also comparable. When the stormtime proton plasma sheet distribution, the source of ring current protons, is left unchanged from its quiet (prestorm) level, we find little difference in proton energy content per unit R (which is geocentric distance normalized by RE) between our double- and single-dip model storms. The protonenergy content of the magnetosphere is roughly increased by a factor of 2.5 by either model storm under this scenario, in which the overall amount of stormtime transport, whether convective or diffusive, is nearly the same for the double- and single-dip model storms. As in our earlier work, we require here an enhanced stormtime plasma sheet population (in addition to enhanced particle transport) in order to achieve (for example) the 20-fold increase in |Dst| characteristic of a large storm. Only when we invoke a two-stage stormtime enhancement of the boundary (plasma sheet) phase space density in combination with the two-stage enhancement in particle transport, our double-dip model storm does show a much larger total energy content than our single-dip model storm with a one-stage enhancement of the boundary spectrum. This suggests that plasma sheet preconditioning may be important for the development of especially intense storms.

The Polar Ionospheric X-ray Imaging Experiment (PIXIE) on NASA's Polar spacecraft provides the first global images of the auroral oval in X-rays and allows very accurate measurements of the timing of geomagnetic disturbances to a degree of temporal resolution not available from previous imagers due to its photon counting characteristics. On October 19, 1998, a magnetic cloud associated with a CME encountered the Earth's magnetopause near 0500 UT, generating a magnetic storm that reached a minimum value in Dst of -139 nT. The z component of the interplanetary magnetic field (IMF) (B z ) remained remarkably steady for the first 10 hours of the storm as did the solar wind particle pressure. The PIXIE and UVI instruments on the Polar spacecraft were both imaging the auroral oval from 0800 to 1800 UT; six distinct impulsive auroral enhancements were observed by the imagers during this time period. Global imaging combined with geosynchronous particle observations allowed classification of the geomagnetic disturbances associated with the events. Only two of the events were classified as substorms; one was classified as a poleward boundary intensification, one was a convection bay, and one was a pseudobreakup. A sixth event occurred after a dramatic northward turning of the IMF at the end of the 10-hour B z south period but was very weak and transient. The effects of the northward turning were counteracted by a simultaneous increase in the B y component of the IMF. The first sign of significant substorm activity occurred over 8 hours after the cloud encountered the Earth and was not associated with any change in the solar wind magnetic field or particle pressure. The cross polar cap potential remained large (> 100 kV), and most of the X-ray emissions observed were associated with enhanced earthward convection caused by large cross-tail electric fields; 50% were collected from the 0000 - 0600 magnetic local time (MLT) sector.

Internal charging has been indicated as the cause of many satellite anomalies. In some cases, it has been argued that internal charging has caused satellite system failures. It may be possible to predict the occurrence of an internal charging threat in the future but that does not remove the necessity to know what the environmental threat may be. The existence, for many years now, of energetic electron and internal charging measurements in the inner magnetosphere provides the ability to identify the threat levels and generate internal charging specifications. The specifications must embody the worst-case environments that can be expected from magnetic storms and extreme solar/interplanetary conditions. Internal-charging environment specifications are needed by satellite manufacturers for setting design requirements for their systems. The specifications are also required for defining the worst-case energetic electron flux levels and total fluence levels from events. These are used for electron beam testing to verify that critical systems are immune to internal charging, for performing tests on subsystems, and for use in anomaly investigation programs. Data from the GOES, LANL, and CRRES satellites were used to develop preliminary internal-charging environment specifications for some commonly used orbits such as geosynchronous and Molniya or high earth orbits (HEO), and they are discussed. A specification is also given for a highly elliptical equatorial orbit that is used for lunar-transfer orbital maneuvers. The preliminary environments were used to estimate the shielding required to reduce worst-case electron fluxes to safe levels for these orbits.

In this study we compare the proton pitch angle distributions (PADs) in the ring current region (L ∼ 3–4) obtained from Combined Release and Radiation Effects Satellite (CRRES) observations during the large magnetic storm (minimum Dst = −170 nT) on August 19, 1991, with results of phase-space mapping simulations in which we trace the bounce-averaged drift of protons during storm-associated enhancements in a model of the convection electric field. We map the phase-space density ƒ according to Liouville's theorem except for attenuation by charge exchange, which we compute for both an empirical model [Rairden et al., 1986] and a theory-based model [Hodges, 1994] of the neutral H density distribution. We compare simulated pitch angle distributions at 48 keV, 81 keV, and 140 keV at L = 3 and L = 4 directly with the CRRES distributions at the same energies and L values before and during the storm. A steady-state application of our transport model, using the empirical neutral H density model of Rairden et al. [1986], reproduces the absolute intensities well except for E = 140 keV at L = 3 (M = 10 MeV/G) and E = 48 keV at L = 4 (M = 13 MeV/G). The anisotropies (A ∼ 0.2–0.8) of the CRRES and modeled pre-storm pitch angle distributions agree within factors ≲ 2. Time-dependent application of our transport model reproduces measured recovery phase anisotropies (t = 10–12 h after storm onset; A ∼ 0.4–1.2) similarly well at the selected energies and L values, but agreement between modeled and measured absolute intensities is energy-dependent and not consistently good. Our model underpredicts the proton intensities found by CRRES for E > 80 keV at L = 4 in early recovery phase (t = 10–12 h). Perhaps the impulsive stormtime convection electric field was stronger during the main phase than we have assumed here. Comparisons were more difficult in late recovery phase (t = 20 h) because CRRES was too far off the magnetic equator. Proton life-times inferred from the CRRES data during the recovery phase of this storm are considerably shorter than charge-exchange lifetimes for either model, but the empirical neutral H density model of Rairden et al. [1986] leads to smaller discrepancies with the CRRES data at all the selected energies and L values than the theory-based neutral H density model of Hodges [1994] for parameters that most closely represent the seasonal and solar maximum conditions of the August 19, 1991, storm. It appears that charge exchange alone is not enough to explain the observed rapid decay of the ring current proton intensities during the recovery phase of this storm.

We employ a three-dimensional ring current model to trace the bounce-averaged drift of singly charged ions during storm-associated enhancements in the convection electric field. Using the simulation results, we map proton phase space density during the main and recovery phases of a storm in accordance with conservation of phase space density ƒ. We map from an initial quiescent phase space distribution that is obtained by solving the steady state transport equation (bounce-averaged charge exchange balancing bounce-averaged radial diffusion) with observed plasma sheet proton spectra as outer boundary conditions. We obtain proton pitch angle distributions at L ∼ 3–4.5 by evaluating ƒ at representative ring current energies (∼20–170 keV). We find that the prestorm and stormtime proton pitch angle anisotropy at any given L between 3 and 4.5 increases with particle energy in agreement with observations. The actual anisotropy at specific energies depends strongly on the shape of the plasma sheet source spectrum at ∼0.5–3 keV. Relatively large enhancements in the stormtime phase space density from the quiescent distribution occurs at all pitch angles for low energies (≲80 keV) except where the quiescent distribution lies on open drift shells. These increases result primarily from stormtime access to L ≲ 4.5 along open drift trajectories from the plasma sheet. For higher-energy (≳150 keV) protons, which are transported via radial diffusion, there is little change in the anisotropy over a 3-hour storm. At intermediate energies (E ∼ 80–150 keV) the stormtime enhancements in the phase space density can vary quite strongly with equatorial pitch angle. For such particles the stormtime transport is intermediate between directly convective and quasi-diffusive, which can complicate the analysis of stormtime pitch angle anisotropies at intermediate energies. Decay lifetimes obtained from CRRES data during the recovery phase of a moderate storm are found to be considerably shorter than charge-exchange lifetimes. It thus appears that charge exchange alone is not enough to explain the observed rapid decay of the proton ring current.

The Magnetospheric Ion Composition Spectrometer onboard the CRRES spacecraft provided mass and charge state composition data for positive ions in the energy-per-charge range 10-425 keV/e. The CRRES data is compared to the AMPTE/CCE observations during both geomagnetically quiet and active periods. The CRRES average radial profiles of H+, He+, and He++ during quiet intervals are remarkably similar to those measured by CCE. The excess of ions measured by CRRES at L

The ring current is a complex system whose dynamics involve particle transport, particle loss, large-scale electric- and magnetic-field variations, and wave generation. This is a review of major advances in ring current modeling, with emphasis on the understanding of processes that lead to ring current formation and decay. Numerical modeling has led to qualitative and quantitative progress in the understanding of such processes. Significant advances have been made in the understanding of charged-particle transport via unsteady convective access and radial diffusion into the ring current region under both quiescent and stormtime conditions. Stormtime decreases in D st (toward more negative values) can be understood quantitatively as the consequence of enhanced access of plasma sheet particles to the ring current region, especially in association with an enhanced stormtime plasma sheet population. Recovery phase (during which D st decays back upward toward zero) is dominated by loss processes such as charge exchange, Coulomb drag, and wave-particle interactions, as radial transport rate declines to pre-storm levels.

[1] We assess whether magnetically and electrically self-consistent ring current simulations can account simultaneously for in situ magnetic field and ion flux measurements in the inner magnetosphere during the large 10 August 2000 storm (min Dst = −107 nT). We use the Rice Convection Model–Equilibrium (RCM-E) and drive it with time-dependent magnetic field, electric field, and plasma boundary conditions that are guided by empirical and assimilative models. Comparisons of the simulated and observed magnetic field from Geostationary Operational Environmental Satellites (GOES) and observed proton differential flux spectra from Los Alamos National Laboratory (LANL) satellites are made at geosynchronous orbit (GEO). Similarly, simulated and observed magnetic field and proton density and temperature are compared along the orbit of Polar (r ∼ 1.8–9 RE) for the event. The simulated and observed magnetic field components agree reasonably well at GEO and along the orbit of Polar. However, since the effects of substorm dipolarizations are not explicitly modeled, the simulation fails to reproduce observed sawtooth fluctuations in the magnetic field. Over energies from 1 to 150 keV, the RCM-E reproduced well the ion dispersion features in the LANL 1994-084 ion differential flux spectra over energies at GEO and proton densities and temperatures calculated from Polar proton flux measurements. Thus, the RCM-E simulations can account simultaneously for in situ magnetic field and ion flux measurements for the 10 August 2000 storm. This demonstrates that a self-consistent model can produce realistic features of the storm time inner magnetosphere.

We perform a phase space mapping study to estimate the enhancement in energy content that results from stormtime particle transport in the equatorial magnetosphere. Our pre-storm phase space distribution is based on a steady-state transport model. Using results from guiding-center simulations of ion transport during model storms having main phases of 3 hr, 6 hr, and 12 hr, we map phase space distributions of ring current protons from the pre-storm distribution in accordance with Liouville's theorem. We find that transport can account for the entire ten to twenty-fold increase in magnetospheric particle energy content typical of a major storm if a realistic stormtime enhancement of the phase space density f is imposed at the nightside tail plasma sheet (represented by an enhancement of f at the neutral line in our model).

This is an investigation of stormtime particle transport that leads to formation of the ring current. Our method is to trace the guiding-center motion of representative ions (having selected first adiabatic invariants mu) in response to model substorm-associated impulses in the convection electric field. We compare our simulation results qualitatively with existing analytically tractable idealizations of particle transport (direct convective access and radial diffusion) in order to assess the limits of validity of these approximations. For mu approximately less than 10 MeV/G (E approximately less than 10 keV at L equivalent to 3) the ion drift period on the final (ring-current) drift shell of interest (L equivalent to 3) exceeds the duration of the main phase of our model storm, and we find that the transport of ions to this drift shell is appropriately idealized as direct convective access, typically from open drift paths. Ion transport to a final closed drift path from an open (plasma-sheet) drift trajectory is possible for those portions of that drift path that lie outside the mean stormtime separatrix between closed and open drift trajectories, For mu approximately 10-25 MeV/G (110 keV approximately less than E approximately less than 280 keV at L equivalent to 3) the drift period at L equivalent to 3 is comparable to the postulated 3-hr duration of the storm, and the mode of transport is transitional between direct convective access and transport that resembles radial diffusion. (This particle population is transitional between the ring current and radiation belt). For mu approximately greater than 25 MeV/G (radiation-belt ions having E approximately greater than 280 keV at L equivalent to 3) the ion drift period is considerably shorter than the main phase of a typical storm, and ions gain access to the ring-current region essentially via radial diffusion. By computing the mean and mean-square cumulative changes in 1/L among (in this case) 12 representative ions equally spaced in drift time around the steady-state drift shell of interest (L equivalent to 3), we have estimated (from both our forward and our time-reversed simulations) the time-integrated radial-diffusion coefficients D(sup sim)(sub LL) for particles having selected values of mu approximately greater than 15 MeV/G. The results agree surprisingly well with the predictions (D(sup ql)(sub LL)) of quasilinear radial diffusion theory, despite the rather brief duration (approximately 3 hrs) of our model storm and despite the extreme variability (with frequency) of the spectral-density function that characterizes the applied electric field during our model storm. As expected, the values of D(sup sim)(sub LL) deduced (respectively) from our forward and time-reversed simulations agree even better with each other and with D(sup sim)(sub LL) when the impulse amplitudes which characterize the individual substorms of our model storm are systematically reduced.

Guiding-center simulations of stormtime transport of ring-current and radiation-belt ions having first adiabatic invariants mu is approximately greater than 15 MeV/G (E is approximately greater than 165 keV at L is approximately 3) are surprisingly well described (typically within a factor of approximately less than 4) by the quasilinear theory of radial diffusion. This holds even for the case of an individual model storm characterized by substorm-associated impulses in the convection electric field, provided that the actual spectrum of the electric field is incorporated in the quasilinear theory. Correction of the quasilinear diffusion coefficient D(sub LL)(sup ql) for drift-resonance broadening (so as to define D(sub LL)(sup ql)) reduced the typical discrepancy with the diffusion coefficients D(sub LL)(sup sim) deduced from guiding-center simulations of representative-particle trajectories to a factor of approximately 3. The typical discrepancy was reduced to a factor of approximately 1.4 by averaging D(sub LL)(sup sim), D(sub LL)(sup ql), and D(sub LL)(sup rb) over an ensemble of model storms characterized by different (but statistically equivalent) sets of substorm-onset times.

[1] By applying plasma sheet boundary conditions based on averages of Geotail data to a magnetically self-consistent ring current simulation model, we investigate how solar-wind influence on plasma sheet conditions affects local-time asymmetries in early ring current development under two representative interplanetary conditions: (1) For strongly northward interplanetary magnetic field (IMF), high solar-wind density, and low solar-wind speed, Geotail ion densities are high and ion temperatures are low, particularly in the post-midnight quadrant at radial distances r > 8 RE; and (2) For weakly northward IMF, high solar-wind speed, and low solar-wind density, a significant density enhancement is not observed in the post-midnight at r > 8 RE. Within an hour after an increase in the convection electric field, Condition (1) lead to relative enhancement of the simulated ring current plasma pressure especially in the post-midnight quadrant, while Condition (2) lead to pressure enhancements that are more uniformly distributed around the night side.

[1] We investigate effects of magnetic self-consistency on ring current development by calculating equatorial particle transport in a model that feeds back the ring current on the magnetospheric configuration. The equatorial magnetic intensity is computed by solving a force-balance equation in the equatorial plane. This force-balance computation is coupled to a kinetic proton and electron drift-loss model. The electric field model used includes corotation, quiescent Volland-Stern convection, and storm-associated enhancements in the convection. We have modeled the 19 October 1998 storm (min Dst = −112 nT) by using the total cross polar cap potential from AMIE to determine the amplitudes of storm-associated electric field enhancements. We trace equatorially mirroring protons and electrons within this model. We have found that self-consistent feedback between plasma pressure and the magnetic field tends to mitigate the energization associated with inward particle transport as the ring current forms. At a given first adiabatic invariant and radial distance, the self-consistent magnetic field reduces the E × B drift rate as it significantly enhances the azimuthal gradient-B drift rate. Especially later in the main phase, there can be places where the plasma pressure and magnetic perturbation are locally enhanced by making the simulation magnetically self-consistent because of enhanced drift rates in regions of reduced magnetic intensity. The southward magnetic perturbation at the center of the Earth, which represents the ring current contribution to the Dst index, is reduced by about 25% by making the simulation magnetically self-consistent. This suggests that simulations that do not take account of the feedback of the ring current overestimate the actual ring current intensity.

[1] Particle flux measurements by the Charge and Mass Magnetospheric Ion Composition Experiment/Magnetospheric Ion Composition Spectrometer (CAMMICE/MICS) and Hydra instruments on the NASA Polar satellite have been used to build empirical models of the plasma environment at low energies in the Earth's inner magnetosphere. These models may be used to develop design and to test specifications for spacecraft surface materials, which are susceptible to damage by the ions. The combination of the CAMMICE/MICS and Hydra models provides the ion flux at energies in the range 20 eV to 200 keV as a function of position in the magnetosphere. For the 1–200 keV energy range, the H+ and O+ ion flux is estimated separately using the CAMMICE/MICS data. Average environments have been calculated for several sample orbital trajectories: a geosynchronous orbit and the orbits of several satellites in the Global Positioning System (GPS) constellation. At high energies (∼100 keV), the flux estimates agree with corresponding estimates from the NASA AP-8 model, but the fluxes at low energies are larger than those extrapolated simply from AP-8. The CAMMICE/MICS model shows that H+ dominates the >2 keV ion populations, but the O+ flux becomes comparable to the H+ flux at ∼1 keV. The standard deviation of both the ion and electron flux was found to be 100–200% of the average value over the entire considered energy range. The average 1–200 keV O+ flux estimates for GEO appear similar to the averages for GPS orbit, so material damage due to O+ in this energy range should be similar for the two orbits.

[1] We investigate the spatial structure of the electron diffuse aurora during the 19 October 1998 storm by comparing drift-loss simulations with precipitating particle data and auroral images. Distributions of precipitating diffuse aurora during magnetic storms depend on variation of the magnetotail electron distributions, electron transport, and electron pitch-angle scattering. In our simulations we compute the bounce-averaged drift motion and precipitation of plasma sheet electrons in Dungey's model magnetosphere (dipole plus uniform southward Bz). We use the Assimilative Model of Ionospheric Electrodynamics (AMIE) electric field. We evaluate the precipitating energy flux and X-ray energy at ionospheric altitude h = 127.4 km for two different scattering rate models: (1) strong diffusion everywhere and (2) an MLT-dependent model scattering rate less than everywhere strong. We compare the simulated distributions of electron energy flux with those obtained from Dst-binned averaged NOAA-12 data and the Polar/Ultraviolet Imager (UVI). The simulated distributions of X-ray flux are compared with Polar/Polar Ionospheric X-ray Imaging Experiment (PIXIE) images. The comparisons reveal that pitch-angle scattering clearly plays a crucial role in determining the spatial distribution of the precipitating electron energy flux. The simulated storm time energy flux with strong diffusion tends to be much more intense in the evening sector and much weaker near dawn than what is statistically observed. The most intense electron precipitation under strong diffusion will occur where the electron drift times from the plasma sheet are on the order of the electron lifetime against strong diffusion. On the other hand, the model and data comparison shows that MLT-dependent scattering less than everywhere strong produces a more realistic electron diffuse aurora than with strong diffusion. Our study strongly suggests that wave scattering is weak in the postdusk sector (∼2200 MLT) and strong in the morning sector (∼0400 MLT), which seems to be in general agreement with statistical and storm time wave observations.

Using drift-loss simulations, we investigate the stormtime ring-current magnetic field produced by protons and electrons during the 19 October 1998 storm. We compute the guiding-center drift motion of equatorially-mirroring protons and electrons in a model magnetosphere and consider H charge exchange loss and electron precipitation due to pitch-angle scattering. We simulate perpendicular particle pressure distributions and the ring-current magnetic field in the equatorial plane. Our quiet-time proton ring current model reproduces a radial perpendicular pressure profile that is similar to statistical observations. Both the proton and electron ring current form asymmetrically early in the storm main phase and become stronger and more nearly symmetric later in the main phase. We find that the quiet-time electron ring-current magnetic field is negligible compared to the quiet-time proton ring-current magnetic field. However, during storms, electrons contribute ∼ 15-20% of protons to the total Dst. Thus, the electrons contribute significantly to the total ring current during storms. There are large asymmetric stormtime ring-current magnetic field depressions at r 0 ∼ 3.5-6 R E . The simulated large magnetic field depressions agree qualitatively with statistical observations. These magnetic field depressions are a significant fraction of the geomagnetic field, indicating a need for a magnetically self-consistent treatment of the particle transport. The large ring-current magnetic depressions should be included in global descriptions of the inner magnetosphere.

[1] We evaluate the relative importance of stormtime ring current electrons to protons by calculating the energy content ratio of electrons to protons for typical ring current energies inferred from observations and simulations. We analyze Explorer 45 measurements taken around the minimum Dst(=−171 nT) of the 17 December 1971 storm. We simulate the electron and proton ring current energy content during a hypothetical storm using drift-loss simulations. From the data analysis, we find that electrons with energies of ∼1–50 keV and protons with energies of ∼10–200 keV contribute the most to the corresponding particle energy content. From both observations and simulations, the ring current electrons contribute only ∼1% as much energy content as ring current protons during quiet times. However, this ratio increases to ∼8–19% during storm main phase. Thus, the ring current electrons can contribute significantly to the ring current energy content during storms.

[1] We seek to determine whether the adiabatic plasma transport and energization resulting from electric and magnetic drift can quantitatively account for the plasma sheet under weak and enhanced convection observed by Geotail presented in the companion paper [Wang et al., 2004]. We use a modified Magnetospheric Specification Model to simulate the dynamics and distributions of protons originating from the deep tail and low-latitude boundary layer (LLBL) under an assigned, slowly increasing convection electric field. The magnetic field is Tsyganenko 96 model, modified so that force balance is maintained along the midnight meridian. Our simulation results reproduce well the observed radial profiles and magnitudes of pressure and magnetic field. The changes of these parameters with convection strength are also well reproduced, indicating that the electric and magnetic drift control the large-scale structure of the plasma sheet. The plasma flows near midnight are diverted toward dusk by diamagnetic drift. We obtain a steady state plasma sheet under strong and steady convection, showing that magnetic drift and field line stretching bring the plasma sheet away from possible convection disruption. The protons from the LLBL strongly affect the plasma sheet density and temperature during quiet times but not during enhanced convection. For the same cross–polar cap potential, stronger shielding of the convection electric field results in smaller energization. The penetration electric field is important in moving the plasma sheet to smaller geocentric radial distance. Our results suggest that the frozen-in condition E = −v × B is not valid in the inner plasma sheet because of strong diamagnetic drift.

[1] During the magnetic storm on October 18–19, 1998 a magnetic cloud encountered the Earth’s magnetosphere. As the cloud passed, the solar wind density decreased dramatically, and as a consequence the solar wind magnetosonic Mach number dropped markedly, approaching 1 at times. Magnetohydrodynamic (MHD) simulations, driven by upstream interplanetary magnetic field (IMF) and solar wind parameters observed on WIND and ACE showed that during the interval of the lowest density, the subsolar distance of the bow shock (BS) reached as much as 50 RE. IMP-8 spacecraft observations of the expansion and subsequent retreat of the BS support the finding that the shock reached a considerable distance upstream. Surprisingly, at times the BS moved sunward at a speed approaching the magnetosonic speed of the solar wind. INDEX TERMS: 2740 Magnetospheric Physics: Magnetospheric configuration and dynamics; 2753 Magnetospheric Physics: Numerical modeling; 2784 Magnetospheric Physics: Solar wind/ magnetosphere interactions. Citation: El-Alaoui, M., R. L. Richard, M. Ashour-Abdalla, and M. W. Chen (2004), Low Mach number bow shock locations during a magnetic cloud event: Observations and magnetohydrodynamic simulations, Geophys. Res. Lett., 31, L03813, doi:10.1029/2003GL018788.

[1] Recent measurements show that magnetospheric convection electric fields during the main phases of magnetic storms are much more complicated in spatial structure than the electric fields that have generally been used to model formation of the stormtime ring current. To investigate the transport effects of such more realistic stormtime electric fields on magnetospheric charged particles, we map the Assimilative Model of Ionospheric Electrodynamics (AMIE) electric potential functions analytically with a simple magnetic field model at selected times of interest during several magnetic storms from 1997–1998 and during the extremely large storm of July 2000. We calculated corresponding contours of constant Hamiltonian (kinetic plus potential energy) for first invariant values that range from 0 to 30 MeV/G (representative of equatorially mirroring cold plasma, ring current, and radiation-belt ions and electrons). These equatorial contours would constitute drift paths if the electric field were truly constant in time. We thus calculated how far along such quasi-drift paths the corresponding particles would have drifted after specific amounts of time, and we compare these quasi-drift characteristics with those obtained from a simple semiempirical model of the convection electric field. We find considerable variability among stormtime equatorial quasi-drift paths, reflecting the known variability of AMIE equipotentials. Patterns of equatorial quasi-drift in the simplified electric field model are (by construction) symmetric about the dawn-dusk meridian. During the main phases of storms, the equatorial electric field derived from AMIE tends to be strongest in an MLT sector several hours wide on the night side. This concentration of AMIE equipotentials provides a channel for rapid transport (requiring ∼20–30 min) for ions with first invariant values representative of the ring current population from the nightside neutral line to low L values (∼3–4) near dusk, where the partial ring current forms. During the extremely large “Bastille Day” storm of 15 July 2000 (minimum Dst = −300 nT) the drift patterns derived from AMIE show penetration of ions to as low as L ∼ 2. This deep penetration of ring current ions could help to account for the very strong ring current that was observed during this storm. The quasi-steady state drift properties help us anticipate the implications of a more realistic electric field model for the particle drifts that lead to the formation of the stormtime ring current.

[1] In order to understand the evolution of the protons and magnetic field in the inner plasma sheet from quiet to disturbed conditions, we incorporate a modified version of the Magnetospheric Specification Model (MSM) with a modified version of the Tsyganenko 96 (T96) magnetic field model to simulate the protons and magnetic field under an increasing convection electric field with two-dimensional (2-D) force balance maintained along the midnight meridian. The local time dependent proton differential fluxes assigned to the model boundary are a mixture of hot plasma from the mantle and cooler plasma from the low latitude boundary layer (LLBL). We previously used this model to simulate the inner plasma sheet under weak convection corresponding to a cross polar cap potential drop (ΔΦPC) equal to 26 kV and obtained 2-D quiet time equilibrium for proton and magnetic field that agrees well with observations. We start our simulation for enhanced convection with this quiet time equilibrium and time-independent boundary particle sources and increase ΔΦPC steadily from 26 to 146 kV in 5 hours. Simulations are also run separately to steady states by keeping ΔΦPC constant after it is increased to 98 and 146 kV. The magnitudes of proton pressure, number density, and temperature and their increase from quiet to moderate activity (ΔΦPC = 98 kV) are consistent with most observations. Our simulation at high activity (ΔΦPC = 146 kV) underestimates the observed pressure and temperature. This disagreement indicates possible dependence of the boundary particle sources on activity and possible effects of solar wind dynamic pressure enhancements that have not yet been included in our simulation. The simulated equatorial pressures and temperatures show stronger enhancement on the dusk side than on the dawn side as convection is increased, while density profiles show an increase on the dawn side and a decrease on the dusk side. The simulated proton flow speed at the equatorial plane increases with enhancing convection while the overall flow direction does not change significantly, a result of enhancement in both the earthward electric drift and the azimuthal diamagnetic drift. The equatorial magnetic field strength decreases more in the near-Earth plasma sheet than at larger radial distances as ΔΦPC increases, resulting in an increasing flat radial profile with enhancing convection. The feedbacks from diamagnetic drift and magnetic fields to increasing convection are found to restrain the pressure increase. Based on the good agreement between our results and observations at moderate activity, our magnetic field indicates that the plasma and magnetic field in the plasma sheet can be in a state far from possible force balance inconsistency during periods of moderately enhanced convection. A scale analysis of our results shows that the frozen-in condition E = −v × B is not valid in the inner plasma sheet for moderate activity.