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We conduct a global hybrid simulation of an observation event to affirm that an interplanetary (IP) shock can drive significant suprathermal (tens to hundreds of eV) H+ outflows from the polar cap. The event showed that a spacecraft in the lobe at ∼6.5 RE altitude above the polar cap observed the appearance of suprathermal outflowing H+ ions about 8 min after observing enhanced downward DC Poynting fluxes caused by the shock impact. The simulation includes H+ ions from both the solar wind and the ionospheric sources. The cusp/mantle region can be accessed by ions from both sources, but only the outflow ions can get into the lobe. Despite that upward flowing solar wind ions can be seen within part of the cusp/mantle region and their locations undergo large transient changes in response to the magnetosphere compression caused by the shock impact, the simulation rules out the possibility that the observed outflowing H+ ions was due to the spacecraft encountering the moving cusp/mantle. On the other hand, the enhanced downward DC Poynting fluxes caused by the shock impact drive more upward suprathermal outflows, which reach higher altitudes a few minutes later, explaining the observed time delay. Also, these simulated outflowing ions become highly field‐aligned in the upward direction at high altitudes, consistent with the observed energy and pitch‐angle distributions. This simulation‐observation comparison study provides us the physical understanding of the suprathermal outflow H+ ions coming up from the polar cap. Key Points: A global hybrid simulation to understand the suprathermal outflowing H+ ions observed in southern lobe driven by an interplanetary shockThe simulated outflowing H+ ions in the lobe are outflows from the polar cap driven by enhanced Poynting fluxes caused by the shock impactThe simulated outflowing H+ ions can account for the observed pitch‐angle distribution and the time delay from the shock impact [ABSTRACT FROM AUTHOR]

To better understand how sharp changes in the solar wind and interplanetary magnetic field conditions affect the ionosphere outflows at high latitudes, we analyze an event observed on 17 July 2002 showing suprathermal (tens to hundreds of eV) outflowing H+ ions in the lobe driven by the impact of an interplanetary (IP) shock. A spacecraft in the lobe at altitudes of ∼6.5 RE first observed enhanced downward DC Poynting fluxes ∼2 min after the shock impact and then, another 8 min later, the appearance of suprathermal outflowing H+ ions as ion beams and ion conics. The increasing downward DC Poynting fluxes and the increasing outflowing H+ fluxes that appeared later were highly correlated because they shared a similar increasing trend with a time scale of ∼5 min. To explain such time delay and correlation, we conclude that a plausible scenario was that the enhanced DC Poynting fluxes reached down to lower altitudes, drove processes to accelerate the pre‐existing polar wind ions to ion beams and ion conics, and then these newly generated suprathermal ions flowed upward to the spacecraft altitudes. This event indicates that an IP shock can drive a significant amount of suprathermal H+ outflows from the polar cap. Key Points: Cluster observed suprathermal outflowing H+ ion beams and ion conics in the lobe after the impact of an interplanetary (IP) shockThe outflowing H+ ions appeared ∼10 min after the shock impact and ∼8 min after enhanced downward DC Poynting fluxesThe suprathermal outflowing H+ ions were likely pre‐existing thermal polar wind being accelerated caused by the enhanced Poynting fluxes [ABSTRACT FROM AUTHOR]

To study the average contributions of the cusp outflow through the lobes and of the nightside auroral outflow to the O+ in the plasma sheet (PS), we performed a statistical study of tailward streaming O+ in the lobes, plasma sheet boundary layer|the plasma sheet boundary layer (PSBL) and the PS, using MMS/Hot Plasma Composition Analyzer (HPCA) data from 2017 to 2020. Similar spatial patterns illustrate the entry of cusp‐origin O+ from the lobes to the PS through the PSBL. There is an YGSM‐dependent energy pattern for the lobe O+, with low‐energy O+ streaming closer to the tail center and high energy (1–3 keV) O+ streaming near the flanks. Low energy (1–100 eV) O+ from the nightside auroral oval is identified in the near‐Earth PSBL/PS with high‐density (>0.02 cm−3), and energetic (>3 keV) streaming O+ with similar density (∼0.013 cm−3) is observed further out on the duskside of the PSBL/PS. The rest of the nightside auroral O+ in the PSBL is mixed with O+ coming in from the lobe, making it difficult to distinguish the source. We estimated the contributions of the different sources of H+ and O+ ions through the PS between 7 and 17 RE, using estimates from this work and data extracted from previous studies. We conclude that, during quiet times, the majority of the near‐Earth PS H+ are from the cusps, the polar wind and Earthward convection from the distant tail. Similarly, while the O+ in the same region has a mixed source, cusp origin outflow provides the highest contribution. Plain Language Summary: We studied the sources of the plasma sheet (PS), using MMS/HPCA data. We observed and mapped the location of the oxygen ions streaming from the dayside cusp region entering the PS through the plasma sheet boundary layer (PSBL). The observations of the oxygen ions from the nightside auroral oval streaming inside PSBL show that this population has higher density than the dayside cusp origin oxygen ions. We estimated the number of the proton and oxygen ions per second entering and leaving the PS and conclude that during quiet times, the solar wind protons are the major source for PS population and ionospheric oxygen ions from dayside cusp is the major source for oxygen ions in the PS. Key Points: Cusp‐source O+ is observed entering the plasma sheet (PS) from the lobe throughout the <25 RE magnetotailThe nightside auroral‐source O+ is identified at <100 eV inside 10 RE, with a more energetic component further out on the dusksideWe estimate that during quiet times, the dayside cusp contributes the most to the near‐earth PS O+ [ABSTRACT FROM AUTHOR]

During geomagnetic storms, the increase in energy input into the ionosphere in the form of Poynting flux and electron precipitation leads to an enhanced ionospheric outflow that results in an increase of the O+ content in the magnetosphere. Using different missions and instrumentation, two main ionospheric sources have been identified for the oxygen ions reaching the inner magnetosphere during geomagnetic storms: the dayside cusp, and the night side auroral region. Evidence of both pathways have been presented in the literature. However, the relative contribution of each of these pathways to the enhancement of O+ observed in near‐Earth plasma sheet, as well as the dynamics involved during the development of geomagnetic storms remains an open question. Here, we present the first statistical study to date to address this question, in the form of a superposed epoch analysis of O+ and H+ moments obtained by the Magnetospheric Multiscale (MMS) mission throughout the main phase of 90 geomagnetic storms with a minimum SYM‐H of at least −50 nT. The results show a clear increase in the oxygen density in the near‐Earth plasma sheet, with values further from Earth remaining low. Temperature values for both species show an increase with the progress of the storms. These results combined suggest that, during the main phase of geomagnetic storms, most of the oxygen ions observed in the near‐Earth plasma sheet are traveling directly from the nightside auroral region. Key Points: Superposed epoch analysis shows dynamic evolution of O+ ions during geomagnetic stormsSignificant enhancement of the O+‐to‐H+ number density ratio observed at radial distances less than 12 REScalar temperature for both species show the arrival of heated ions far from Earth throughout the analyzed period [ABSTRACT FROM AUTHOR]

We present a case study of the H+, He+, and O+ low‐energy "finger" structure observed by the Van Allen Probe A Helium, Oxygen, Proton, and Electron (HOPE) spectrometer on 26 October 2016. This structure, whose characteristic energy is from approximately tens of eV to a few keV, looks like a "finger" that is rich in O+ and He+, faint in H+ on an energy‐time spectrogram. By using the Space Weather Modeling Framework (SWMF) and Weimer05 electric fields, combined with a dipole or more self‐consistent magnetohydrodynamic (MHD) magnetic field, backward tracing of O+ reveals that the structure is formed by ions with a long drift time from the plasma sheet during the magnetic storm main phase to the inner region with trajectories dominated by eastward drift motion, and the formation depends on the convection electric field model. The heavy ion dominance of the feature is explained by charge exchange losses along the long slow drift paths. Plain Language Summary: Since the early 1970s, a common way to display data from satellite missions in the Earth's magnetosphere is the energy spectrogram, where the flux of observed particles is displayed as a function of particles' energy and the observation time. In this format, many different spectral features have been observed in different regions of the magnetosphere and simulations have been used to understand the formation of these features. Often, these simulations use empirical electric models and dipole magnetic field approximation and observed spectral structures are not able to be replicated. This study investigates the formation mechanism of a type of feature named low‐energy "finger" observed by Van Allen Probe A, using the Space Weather Modeling Framework (SWMF), the Weimer05 electric field as a comparison, combined with a dipole or MHD magnetic field. We find that the inner boundary and the enhanced convection electric field, the source population and the charge exchange losses along the drift paths play a very important role for the formation of this "finger" structure. Key Points: A low‐energy "finger" structure deep in the inner magnetosphere is formed by drift of ions from the plasma sheet during storm main phaseSimulations using the SWMF electric field reproduce the structure much better than using the Weimer05 modelThe heavy ion dominance of the feature is explained by the charge exchange losses along the long slow drift paths [ABSTRACT FROM AUTHOR]

We use the UNH‐IMEF electric field model to simulate the convection of O+ from the near‐earth plasma sheet into the ring current during the 17 March 2015 storm. Using Van Allen Probes data from the night side apogee, we reconstruct a realistic O+ source. Modeling this storm using the UNH‐IMEF electric field and a dipole magnetic field has previously been found to have good agreement. Using the realistic source along with drift times and charge exchange loss from these results, we model an inbound pass near the peak of the storm where O+ is increasingly dominant over H+. We find that the time‐varying realistic O+ source is necessary to reproduce the observed spectral features and the O+ pressure enhancements at low L‐shells, while our previous results showed that the H+ was able to be modeled sufficiently with a simple, unchanging boundary condition. Further, our results show that adiabatic convective transport of O+ from the near‐earth plasma sheet (L ~ 6) can explain the observed ring current enhancements. Key Points: Numerous substorm‐related O+ enhancements were observed during the main phase of the 17 March 2015 stormA dynamic O+ nightside source that can capture temporal enhancements on the substorm scale better reproduces the observed ring currentInward adiabatic convective transport of the dynamic enhanced plasma sheet O+ explains the dominant O+ ring current during the storm [ABSTRACT FROM AUTHOR]

Energetic O+ outflow is observed from both the dayside cusp and the nightside aurora, but the relative importance of these regions in populating the plasma sheet and ring current is not known. During a storm on 16 July 2017, the Arase and MMS satellites were located in the near‐earth and midtail plasma sheet boundary layers (PSBL). During the storm main phase, Arase and MMS both observe O+ in the lobe entering the PSBL, followed by a time period with energy‐dispersed bursts of tailward‐streaming O+. The ions at MMS are at higher energies than at Arase. Trajectory modeling shows that the ions coming in from the lobe are cusp origin, while the more energetic bursty ions are from the nightside aurora. The observed and simulated energies and temporal dispersion are consistent with these sources. Thus, both regions directly contribute O+ to the plasma sheet during this storm main phase. Plain Language Summary: The magnetosphere is the region of space encompassed by Earth's magnetic field. The plasma trapped in the magnetosphere can come both from the Sun and from the ionosphere, the ionized layer of the atmosphere. The ionospheric contribution to the plasma increases during geomagnetic storms. These ions get energized in the auroral oval and flow out along magnetic field lines. During storms, this outflow can contain a large fraction of O+. There are two particular regions where this O+ outflow occurs, one on the dayside and one on the nightside. This study looks at the contribution of O+ from these two regions. Two spacecraft in different locations in the magnetosphere during the storm were able to observe the signatures of ions from both regions indicating that both regions are important during the peak of the storm. Key Points: Arase and MMS are fortuitously located in the near‐Earth and midtail plasma sheet boundary layer during the main phase of a stormBoth spacecraft observe O+ from both the nightside aurora and the cusp, with higher energies observed at greater distancesThe energy differences and timing of the O+ at the two spacecraft are consistent with modeled transport [ABSTRACT FROM AUTHOR]