Using the Cluster/Composition and Distribution Function (CODIF) analyzer data set from 2001 to 2013, a full solar cycle, we determine the ion distributions for H+, He+, and O+ in the inner ...magnetosphere (L < 12) over the energy range 40 eV to 40 keV as a function magnetic local time, solar EUV (F10.7), and geomagnetic activity (Kp). Concentrating on L = 6–7 for comparison with previous studies at geosynchronous orbit, we determine both the average flux at 90° pitch angle and the pitch angle anisotropy as a function of energy and magnetic local time. We clearly see the minimum in the H+ spectrum that results from the competition between eastward and westward drifts. The feature is weaker in O+ and He+, leading to higher O+/H+ and He+/H+ ratios in the affected region, and also to a higher pitch angle anisotropy, both features expected from the long‐term effects of charge exchange. We also determine how the nightside L = 6–7 densities and temperatures vary with geomagnetic activity (Kp) and solar EUV (F10.7). Consistent with other studies, we find that the O+ density and relative abundance increase significantly with both Kp and F10.7. He+ density increases with F10.7, but not significantly with Kp. The temperatures of all species decrease with increasing F10.7. The O+ and He+ densities increase from L = 12 to L ~ 3–4, both absolutely and relative to H+, and then drop off sharply. The results give a comprehensive view of the inner magnetosphere using a contiguous long‐term data set that supports much of the earlier work from GEOS, ISEE, Active Magnetospheric Particle Tracer Explorers, and Polar from previous solar cycles.
Key Points
We determine inner magnetosphere ion composition as a function of energy and MLT over a solar cycle
Changes in the MLT dependence of the spectra with F10.7 indicate changes in the convection pattern
Regions of high O+/H+ and He+/H+ on the dayside indicate effects of charge exchange loss
Abstract
Both solar wind and ionospheric sources contribute to the magnetotail plasma sheet, but how their contribution changes during a geomagnetic storm is an open question. The source is critical ...because the plasma sheet properties control the enhancement and decay rate of the ring current, the main cause of the geomagnetic field perturbations that define a geomagnetic storm. Here we use the solar wind composition to track the source and show that the plasma sheet source changes from predominantly solar wind to predominantly ionospheric as a storm develops. Additionally, we find that the ionospheric plasma during the storm main phase is initially dominated by singly ionized hydrogen (H
+
), likely from the polar wind, a low energy outflow from the polar cap, and then transitions to the accelerated outflow from the dayside and nightside auroral regions, identified by singly ionized oxygen (O
+
). These results reveal how the access to the magnetotail of the different sources can change quickly, impacting the storm development.
A Case Study on the Origin of Near‐Earth Plasma Glocer, A.; Welling, D.; Chappell, C. R. ...
Journal of geophysical research. Space physics,
November 2020, Letnik:
125, Številka:
11
Journal Article
Recenzirano
Odprti dostop
This study presents simulations of the coupled space environment during a geomagnetic storm that separates the different sources of near‐Earth plasma. These simulations include separate fluids for ...solar wind and ionospheric protons, ionospheric oxygen, and the plasmasphere. Additionally, they include the effects of both a hot ring current population and a cold plasmaspheric population simultaneously for a geomagnetic storm. The modeled ring current population represents the solution of bounce‐averaged kinetic solution; the core plasmaspheric model assumes a fixed temperature of 1 eV and constant pressure along the field line. We find that during the storm, ionospheric protons can be a major contributor to the plasmasheet and ring current and that ionospheric plasma can largely displace solar wind protons in much of the magnetosphere under certain conditions. Indeed, the ionospheric source of plasma cannot be ignored. Significant hemispheric asymmetry is found between the outflow calculated in the summer and winter hemispheres, consistent with past observations. That asymmetric outflow is found to lead to asymmetric filling of the lobes, with the northern (summer) lobe receiving more outflow that has a higher proportion of O+ and the southern (winter) lobe receiving less outflow with a higher proportion of H+. We moreover find that the inclusion of the plasmasphere can have a system‐wide impact. Specifically, when the plasmasphere drainage plume reaches the magnetopause, it can reduce the reconnection rate, suppress ionospheric outflow and change its composition, change the composition in the magnetosphere, and reduce the ring current intensity.
Key Points
Ionospheric H+ is a critically important contributor to the magnetosphere during a storm
Seasonal effect on outflow create asymmetric filling of the lobes
The inclusion of an additional plasmaspheric fluid has system‐wide effects
Mesoscale structures in Earth's magnetotail are a primary feature of particle transport to the inner magnetosphere during storms and substorms. We demonstrate that such structures can be observed in ...energetic neutral atom (ENA) data which can provide remote, global images of the magnetosphere. In particular, we present localized regions of increased ion temperatures that appear in equatorial ion temperature maps calculated from Two Wide‐angle Imaging Neutral‐atom Spectrometers (TWINS) ENA data. These regions are associated with a dipolarization front with bursty ion flows measured by Magnetospheric MultiScale (MMS) and are concurrent with substorm features observed in field aligned currents (FAC) from Active Magnetosphere and Planetary Electrodynamics Response Experiment measurements. We conduct a magnetohydrodynamics simulation of the same event and show simulated ion temperatures, ion flows, and FACs that agree with the measurements. However, the observed plasma heating is less intense in the simulated results than in the TWINS and MMS data, indicating that some heating processes may be missing from the model.
Plain Language Summary
Large chunks of energetic particles and enhanced magnetic field from the Sun can cause geomagnetic storms and substorms in the space surrounding Earth. During these active times, the energy from the Sun can get dumped into the nightside where ions and electrons are heated and propelled toward the Earth like from a slingshot. When these energetic particles get closer to the Earth, they can disrupt satellites and cause power outages, so scientists hope to improve our understanding and develop forecasting tools for these storms and substorms. Scientists have shown that the particles move toward the Earth in narrow channels. We demonstrate that these channels are heated and can be seen in temperature maps created from the NASA TWINS mission. To support our findings, we also compare the results to measurements from other satellites and computer simulations. This means that we can use such maps for more research and to improve forecasting models. For example, we found that the measured temperatures are higher than the simulated temperatures, indicating that more is needed in the models. We could also use a satellite like TWINS to act as a warning system for storms and substorms.
Key Points
An interval of bursty flows during a magnetospheric substorm expansion phase is observed by Two Wide‐angle Imaging Neutral‐atom Spectrometers (TWINS), Magnetospheric MultiScale (MMS), and Active Magnetosphere and Planetary Electrodyamics Response Experiment and simulated using the Space Weather Modeling Framework
The localized regions of ion heating observed by TWINS are directly related to the bursty plasma flow channel and substorm development
The observed heating is less intense in the simulations than the TWINS and MMS data; additional heating processes are needed in the model
We use an E × B‐driven plasmapause test particle (PTP) simulation to provide global contextual information for in situ measurements by the Van Allen Probes (Radiation Belt Storm Probes (RBSP)) during ...15–20 January 2013. During 120 h of simulation time beginning on 15 January, geomagnetic activity produced three plumes. The third and largest simulated plume formed during enhanced convection on 17 January, and survived as a rotating, wrapped, residual plume for tens of hours. To validate the simulation, we compare its output with RBSP data. Virtual RBSP satellites recorded 28 virtual plasmapause encounters during 15–19 January. For 26 of 28 (92%) virtual crossings, there were corresponding actual RBSP encounters with plasmapause density gradients. The mean difference in encounter time between model and data is 36 min. The mean model‐data difference in radial location is 0.40 ± 0.05 RE. The model‐data agreement is better for strong convection than for quiet or weakly disturbed conditions. On 18 January, both RBSP spacecraft crossed a tenuous, detached plasma feature at approximately the same time and nightside location as a wrapped residual plume, predicted by the model to have formed 32 h earlier on 17 January. The agreement between simulation and data indicates that the model‐provided global information is adequate to correctly interpret the RBSP density observations.
Key Points
Model nightside plasmapause encounters agree with observations to within 0.4 REBoth RBSP satellites crossed features consistent with a 32 h old residual plumeModel‐provided global context is adequate to interpret in situ density data
We have used the ion composition data from the CIS/CODIF instrument on Cluster to determine how the O+ population in the plasma sheet and the adjacent lobes changes during geomagnetic storms. The ...Cluster trajectory, which moves over the polar cap, into the lobe, and then into the plasma sheet on each orbit, allows us to track the changes in O+ in these regions for a prestorm orbit, main‐phase orbit, and recovery phase orbit. We find that changes in the O+ density and pressure in the plasma sheet are similar to those commonly observed in the ring current during a storm. The O+ is low prestorm. It increases by about a factor of 10 just prior to or during the early main phase of the storm, and is reduced, but usually not down to prestorm levels, in the recovery phase. The lobes contain tailward streaming O+ which originates in the “cleft ion fountain”. During the storms main phase, this population also increases. A detailed look at the main‐phase passes shows that a significant increase in the O+/H+ ratio is observed when this lobe population reaches the plasma sheet, and the tailward streaming O+ is observed continuously as the spacecraft moves from the lobe into the plasma sheet. The enhanced O+ in the lobe and the plasma sheet is observed for many hours during the storm. The inward convection of this population is likely a significant contributor to the storm time ring current.
Gyroresonant wave‐particle interactions with very low frequency whistler mode chorus waves can accelerate subrelativistic seed electrons (hundreds of keV) to relativistic energies in the outer ...radiation belt during geomagnetic storms. In this study, we conduct a superposed epoch analysis of the chorus wave activity, the seed electron development, and the outer radiation belt electron response between L* = 2.5 and 5.5, for 25 coronal mass ejection and 35 corotating interaction region storms using Van Allen Probes observations. Electron data from the Magnetic Electron Ion Spectrometer and Relativistic Electron Proton Telescope instruments are used to monitor the storm‐phase development of the seed and relativistic electrons, and magnetic field measurements from the Electric and Magnetic Field Instrument Suite and Integrated Science instrument are used to identify the chorus wave activity. Our results show a deeper (lower L*), stronger (higher flux), and earlier (epoch time) average seed electron enhancement and a resulting greater average radiation belt electron enhancement in coronal mass ejection storms compared to the corotating interaction region storms despite similar levels and lifetimes of average chorus wave activity for the two storm drivers. The earlier and deeper seed electron enhancement during the coronal mass ejection storms, likely driven by greater convection and substorm activity, provides a higher probability for local acceleration. These results emphasize the importance of the timing and the level of the seed electron enhancements in radiation belt dynamics.
Key Points
Van Allen Probes statistical study of seed electrons and chorus activity during CME and CIR storms
Seed electrons have a stronger, earlier, and deeper penetrating average enhancement during CME‐driven storms than CIR‐driven storms
A greater occurrence of radiation belt enhancements is observed during CME‐driven storms than CIR‐driven storms
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 storm
Both spacecraft observe O+ from both the nightside aurora and the cusp, with higher energies observed at greater distances
The energy differences and timing of the O+ at the two spacecraft are consistent with modeled transport
The source of O+ in the storm time ring current Kistler, L. M.; Mouikis, C. G.; Spence, H. E. ...
Journal of geophysical research. Space physics,
June 2016, 2016-06-00, 20160601, Letnik:
121, Številka:
6
Journal Article
Recenzirano
Odprti dostop
A stretched and compressed geomagnetic field occurred during the main phase of a geomagnetic storm on 1 June 2013. During the storm the Van Allen Probes spacecraft made measurements of the plasma ...sheet boundary layer and observed large fluxes of O+ ions streaming up the field line from the nightside auroral region. Prior to the storm main phase there was an increase in the hot (>1 keV) and more isotropic O+ ions in the plasma sheet. In the spacecraft inbound pass through the ring current region during the storm main phase, the H+ and O+ ions were significantly enhanced. We show that this enhanced inner magnetosphere ring current population is due to the inward adiabatic convection of the plasma sheet ion population. The energy range of the O+ ion plasma sheet that impacts the ring current most is found to be from ~5 to 60 keV. This is in the energy range of the hot population that increased prior to the start of the storm main phase, and the ion fluxes in this energy range only increase slightly during the extended outflow time interval. Thus, the auroral outflow does not have a significant impact on the ring current during the main phase. The auroral outflow is transported to the inner magnetosphere but does not reach high enough energies to affect the energy density. We conclude that the more energetic O+ that entered the plasma sheet prior to the main phase and that dominates the ring current is likely from the cusp.
Key Points
Auroral outflow during the storm main phase mainly impacts <1 keV plasma sheet population
The >1 keV (hot) more isotropic plasma sheet O+ population increases prior to the main phase
Inward transport of the hot O+ dominates the ring current; this O+ is likely from the cusp
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