We present the first global geospace simulation to reproduce auroral giant undulations (GUs). To identify their magnetospheric drivers, we employ the MAGE (Multiscale Atmosphere-Geospace Environment) model in a case study of a geomagnetic storm for which there were spacecraft- and ground-based observations of GUs. The model reproduces the spatial and temporal scales of the GUs as well as the presence of duskside subauroral polarization streams (SAPS) and plasmapause undulations. Based on our modeling, we are able to identify the magnetospheric drivers of GUs as mesoscale ring current injections which, after drifting westward, create inverted regions of flux-tube entropy (FTE) and subsequent interchange instability. Outward-protruding interchange fingers disrupt shielding of the inner magnetosphere, creating longitudinally-localized ripples in magnetospheric convection equatorward of the magnetospheric instability, which structure the plasmapause and duskside diffuse precipitation. While not causal, SAPS and plasmapause undulations are a consequence of the unstable magnetospheric configuration.

The geospace plume, referring to the combined processes of the plasmaspheric and the ionospheric storm-enhanced density (SED)/total electron content (TEC) plumes, is one of the unique features of geomagnetic storms. The apparent spatial overlap and joint temporal evolution between the plasmaspheric plume and the equatorial mapping of the SED/TEC plume indicate strong magnetospheric-ionospheric coupling. However, a systematic modeling study of the factors contributing to geospace plume development has not yet been performed due to the lack of a sufficiently comprehensive model including all the relevant physical processes. In this paper, we present a numerical simulation of the geospace plume in the March 31, 2001 storm using the Multiscale Atmosphere Geospace Environment model. The simulation reproduces the observed linkage of the two plumes, which, we interpret as a result of both being driven by the electric field that maps between the magnetosphere and the ionosphere. The model predicts two velocity channels of sunward plasma drift at different latitudes in the dusk sector during the storm main phase, which are identified as the sub-auroral polarization stream (SAPS) and the convection return flow, respectively. The SAPS is responsible for the erosion of the plasmasphere plume and contributes to the ionospheric TEC depletion in the midlatitude trough region. We further find the spatial distributions of the magnetospheric ring current ions and electrons, determined by a delicate balance of the energy-dependent gradient/curvature drifts and the E´B drifts, are crucial to sustain the SAPS electric field that shapes the geospace plume throughout the storm main phase.

The High-latitude Ionosphere Dynamics for Research Applications (HIDRA) model is part of the Multiscale Atmosphere-Geospace Environment (MAGE) model under development by the Center for Geospace Storms (CGS) NASA DRIVE Science Center. This study employs HIDRA to simulate upflows of H+, He+, O+, and N+ ions, with a particular focus on the relative N+ concentrations, production and loss mechanisms, and thermal upflow drivers as functions of season, solar activity, and magnetospheric convection. The simulation results demonstrate that N+ densities typically exceed He+ densities, N+ densities are typically ~10% O+ densities, and N+ concentrations at quiet-time are approximately 50-100% of N+ concentrations during storm-time. Furthermore, the N+ and O+ upflow fluxes show similar trends with variations in magnetospheric driving. The inclusion of ion-neutral chemical reactions involving metastable atoms is shown to have significant effects on N+ production rates. With this metastable chemistry included, the simulated ion density profiles compare favorably with satellite measurements from Atmosphere Explorer C (AE-C) and Orbiting Geophysical Observatory 6 (OGO-6).

The formation of the stormtime ring current is a result of the inward transport and energization of plasma sheet ions. Previous studies have demonstrated that a significant fraction of the total inward plasma sheet transport takes place in the form of bursty bulk flows (BBFs), known theoretically as flux tube entropy-depleted “bubbles.’ However, it remains an open question to what extent bubbles contribute to the buildup of the stormtime ring current. Using the Multiscale Atmosphere Geospace Environment (MAGE) Model, we present a case study of the March 17, 2013 storm, including a quantitative analysis of the contribution of plasma transported by bubbles to the ring current. We show that bubbles are responsible for at least 50\% of the plasma energy enhancement within 6 R$_E$ during this strong geomagnetic storm. The bubbles that penetrate within 6 R$_E$ transport energy primarily in the form of enthalpy flux, followed by Poynting flux and relatively little as bulk kinetic flux. Return flows can transport outwards a significant fraction of the plasma energy being transported by inward flows, and therefore must be considered when quantifying the net contribution of bubbles to the energy buildup. Data-model comparison with proton intensities observed by the Van Allen Probes show that the model accurately reproduces both the bulk and spectral properties of the stormtime ring current. The evolution of the ring current energy spectra throughout the modeled storm is driven by both inward transport of an evolving plasma sheet population and by charge exchange with Earth’s geocorona.

We simulated the Nov 4, 2021 geomagnetic storm event penetrating electric field using the Multiscale Atmosphere-Geospace Environment (MAGE) and compared with the NASA ICON observation. The ICON observation showed enhancement of the vertical ion drift when the penetrating electric field arrived at the equatorial region. The simulated vertical ion drifts are consistent with ICON observation. Hence, we are able to verify the MAGE simulation with ICON observation. On the dusk side, the MAGE simulation showed strong pre-reversal enhancement (PRE), whereas the ICON observation did not display any sign of the PRE. The MAGE simulation did show that PRE amplitude decreases as altitude increase. Because the ICON orbital height is above the model upper boundary, it could be a factor for the discrepancy. Instrumental issue cannot be ruled out at this moment. GOLD UV image at the same time exhibits multiple plasma bubbles, which seem to suggest the existence of the PRE.

Solar eruptions cause geomagnetic storms in the near-Earth environment, creating spectacular aurorae visible to the human eye and invisible dynamic changes permeating all of geospace. Just equatorward of the aurora, radars and satellites often observe intense westward plasma flows called subauroral polarization streams (SAPS) in the dusk-to-midnight ionosphere. SAPS occur across a narrow latitudinal range and lead to intense frictional heating of the ionospheric plasma and atmospheric neutral gas. SAPS also generate small-scale plasma waves and density irregularities that interfere with radio communications. As opposed to the commonly observed duskside SAPS, intense eastward subauroral plasma flows in the morning sector were recently discovered to have occurred during a super storm on 20 November 2003. However, the origin of these flows termed “dawnside SAPS” could not be explained by the same mechanism that causes SAPS on the duskside and has remained a mystery. Through real-event global geospace simulations, here we demonstrate that dawnside SAPS can only occur during major storm conditions. During these times the magnetospheric plasma convection is so strong as to effectively transport ions to the dawnside, whereas they are typically deflected to the dusk by the energy-dependent drifts. Ring current pressure then builds up on the dawnside and drives field-aligned currents that connect to the subauroral ionosphere, where eastward SAPS are generated. The origin of dawnside SAPS explicated in this study advances our understanding of how the geospace system responds to strongly disturbed solar wind driving conditions that can have severe detrimental impacts on human society and infrastructure.

Long-lasting Pc5 ultralow frequency (ULF) waves spanning the dayside and extending from L~5.5 into the polar cap region were observed by conjugate ground magnetometers. Observations from MMS satellites in the magnetosphere and magnetometers on the ground confirmed that the ULF waves on closed field lines were due to fundamental toroidal field line resonances (FLRs). Monochromatic waves at lower latitudes tended to maximize their power away from noon in both the morning and afternoon sectors, while more broadband waves at higher latitudes tended to have a wave power maximum near noon. The wave power distribution and anti-sunward wave propagation suggest surface waves on a Kelvin-Helmholtz (KH) unstable magnetopause coupled with FLRs. Based on satellite observations in the foreshock/magnetosheath, the more turbulent ion foreshock during an extended period of radial interplanetary magnetic field (IMF) likely plays an important role in providing seed perturbations for the growth of the KH waves.

An interplanetary shock can abruptly compress the magnetosphere, excite magnetospheric waves and field-aligned currents, and cause a ground magnetic response known as a sudden commencement (SC). However, the transient (<~1 min) response of the ionosphere-thermosphere system during an SC has been little studied due to limited temporal resolution in previous investigations. Here, we report observations of a global reversal of ionospheric vertical plasma motion during an SC on 24 October 2011 using ~6 s resolution SuperDARN ground scatter data. The dayside ionosphere suddenly moved downward during the magnetospheric compression due to the SC, lasting for only ~1 min before moving upward. By contrast, the post-midnight ionosphere briefly moved upward then moved downward during the SC. Simulations with a coupled geospace model suggest that the reversed E X B vertical drift is caused by a global reversal of ionospheric zonal electric field induced by magnetospheric compression during the SC.

Thermospheric mass density perturbations are commonly observed during geomagnetic storms. The sources of these perturbations have not been well understood. In this study, we investigated the thermospheric density perturbations observed by the CHAMP and GRACE satellites during the 24-25 August 2005 geomagnetic storm. The observations show that large neutral density enhancements occurred not only at high latitudes, but also globally. In particular, large density perturbations were seen in the equatorial regions away from the high-latitude, magnetospheric energy sources. We used the high-resolution Multiscale Atmosphere Geospace Environment (MAGE) model to reproduce the consecutive neutral density changes observed by the satellites during the storm. The MAGE simulation, which resolved mesoscale high-latitude convection electric fields and field-aligned currents, and included a physics-based specification of the auroral precipitation, was contrasted with a standalone ionosphere-thermosphere simulation driven by an empirical model of the high-latitude electrodynamics. The comparison demonstrates that a first-principles representation of highly dynamic and localized Joule heating events in a fully coupled whole geospace model such as MAGE is critical to accurately capturing both the generation and propagation of traveling atmospheric disturbances (TADs) that produce neutral density perturbations globally. In particular, the MAGE simulation shows that the larger density peaks in the equatorial region that are observed by CHAMP and GRACE are the results of TADs, generated at high latitudes in both hemispheres, propagating to and interfering at lower latitudes. This study reveals the importance of investigating thermospheric density variations in a fully coupled geospace model with sufficiently high resolving power.

The role of diffuse electron precipitation in forming subauroral polarization streams (SAPS) is investigated with the Multiscale Atmosphere-Geospace Environment (MAGE) model. Diffuse precipitation is derived from the distribution of drifting electrons calculated in MAGE. SAPS manifest themselves as a separate mesoscale flow channel in the duskside ionosphere when diffuse precipitation is implemented in MAGE, whereas it merges with the primary auroral convection when diffuse precipitation is turned off. SAPS overlap with the downward Region-2 field-aligned currents equatorward of diffuse precipitation, where poleward electric fields closing the Pedersen currents are strong due to a low conductance in the subauroral ionosphere. The Region-2 field-aligned currents extend to lower latitudes than diffuse precipitation because the ring current protons penetrate closer to the Earth than the electrons do. This study demonstrates the critical role of diffuse electron precipitation in determining SAPS location and structure.

Using the newly developed, Multiscale Atmosphere-Geospace Environment (MAGE) model, we simulated the penetrating electric field in the equatorial region under different interplanetary magnetic field (IMF) Bz conditions during September 2020. Two intervals were selected for detailed analysis with the vertical ion drift data from the NASA ICON. The MAGE simulations show that in southward IMF (S-IMF) cases, the dawn-dusk electric potential drop at the equator is about 14% of the cross polar cap potential difference. The dawn-dusk potential drop at the equator varies instantaneously with the changes in the IMF Bz or interplanetary electric field, which in turn alters the vertical ion drift. The daytime changes of the equatorial vertical ion drift in response to the penetrating electric field related to the IMF Bz are only half of that during the nighttime, due mostly to the E-region dynamo. MAGE simulation shows pre-reversal enhancement (PRE) during southward IMF cases, but the PRE was absent in the ICON IVM observations. Further observations and modeling are needed to resolve this discrepancy.

Strong subauroral plasma flows were observed in the dawnside ionosphere during the 20 November 2003 super geomagnetic storm. They are identified as dawnside subauroral polarization streams (SAPS) in which plasma drift direction is eastward and opposite to the westward SAPS typically found in the dusk sector. Both dawnside and duskside SAPS are driven by the enhanced meridional electric field in the low latitude portion of Region-2 field-aligned currents (FACs) in the subauroral region where ionospheric conductance is relatively low. However, dawnside eastward SAPS were only observed in the main and recovery phases while duskside westward SAPS were found much earlier before the sudden storm commencement. Simulations with the Multiscale Atmosphere-Geospace Environment (MAGE) model demonstrate that the eastward SAPS are associated with dawnside ring current build-up. Unlike the duskside where ring current build-up and SAPS formation can occur under moderate driving conditions, strong magnetospheric convection is required for plasmasheet ions to overcome their energy-dependent drifts to effectively build up the dawnside ring current and upward Region-2 FACs. We further used test particle simulations to show the characteristic drift pattern of energetic protons under strong convection conditions and how they are related to the dawnside SAPS occurrence. This study demonstrates the connection between the level of solar wind driving condition and a rare ionospheric structure, eastward SAPS on the dawnside, which only occur under strong convection typically associated with intense or super storms. Dawnside SAPS are suggested as a unique feature of major geomagnetic storms.