Plasmaspheric Plume Research Articles

Migration of Fast Magnetosonic Waves in the Magnetosphere With a Plasmaspheric Plume

AbstractPlasmaspheric density structures are considered to control the propagation trajectories of fast magnetosonic (MS) waves in the inner magnetosphere. However, whether the plasmaspheric plume can effectively alter the propagation of MS waves remains unknown. Based on the analytical model of plasma density, ray tracing simulations are performed to investigate the propagation of exactly perpendicular MS waves in the equatorial plane in the magnetosphere containing a plasmaspheric plume. We find that plasmatrough and plume MS waves propagating toward the plasmaspheric plume can be reflected into the plasmaspheric core by the plume, then potentially migrating globally and thus quasi‐trapped inside the plasmaspheric core. The simulations also indicate that lower‐frequency MS waves approaching the plasmaspheric plume are more easily reflected and quasi‐trapped inside the plasmaspheric core. Our findings illustrate a previously unexplored way that plasmatrough MS waves could access and be trapped inside the plasmaspheric core via azimuthal plasmaspheric density structures.

Large Amplitude Whistler Waves in Earth's Plasmasphere and Plasmaspheric Plumes

AbstractWhistler mode waves in the plasmasphere and plumes drive significant losses of energetic electrons from the Earth's radiation belts into the upper atmosphere. In this study, we conducted a survey of amplitude‐dependent whistler wave properties and analyzed their associated background plasma conditions and electron fluxes in the plasmasphere and plumes. Our findings indicate that extremely large amplitude (>400 pT) whistler waves (a) tend to occur at L > 4 over the midnight‐dawn‐noon sectors and have small wave normal angles; (b) are more likely to occur during active geomagnetic conditions associated with higher fluxes of anisotropic electrons at 10 s keV energies; and (c) tend to occur at higher latitudes up to 20° with increasing amplitude. These results suggest that extremely large amplitude whistler waves in the plasmasphere and plumes could be generated locally by injected electrons during substorms and further amplified when propagating to higher latitudes.

Statistical Properties of Pc4‐5 ULF Waves in Plasmaspheric Plumes

AbstractUltra‐low‐frequency (ULF) waves emerge as pivotal factors in elucidating the mechanisms that drive the intricate dynamics of radiation belt electrons within the plasmasphere and plasmaspheric plumes. Utilizing THEMIS data from September 2012 to September 2017, we conducted a comprehensive statistical analysis of Pc4‐5 ULF waves within and outside the plasmaspheric plume. Our findings reveal a distinctive dawn‐dusk asymmetry in occurrence rate and wave power of poloidal mode waves in the absence of the plume, resembling the toroidal mode asymmetry observed. Poloidal mode waves exhibit a higher likelihood of formation within the plume, while the toroidal mode waves show the opposite trend, contributing to the elevated dusk‐side occurrence rate of poloidal mode waves. Moreover, both wave modes within the plume demonstrate lower peak frequencies compared to waves outside the plume. The global distribution of wave power within the plume suggests higher power at noon than on the dusk side.

Long Lifetime Hiss Rays in the Disturbed Plasmasphere

AbstractPlasmaspheric hiss waves are important to shape the Earth’s electron radiation belt. These waves are commonly envisioned to have a long lifetime which allows them to permeate the global plasmasphere from a spatially restricted source. However, this hypothesis has not been experimentally confirmed yet, because of the challenging observational requirements in terms of location and timing. With wave and particle measurements from five magnetospheric satellites and detailed modeling, we present the first report of long lifetime (∼42 s) hiss rays in the substorm‐disturbed plasmasphere. The low‐frequency hiss waves are found to originate from the middle piece of the plasmaspheric plume, bounce between two hemispheres, and eventually drift into the plasmaspheric core. These hiss rays can travel through ∼3 hr magnetic local time and ∼4 magnetic shell. Such a long‐time and large‐scale permeation of hiss rays could benefit from the ducting process by plasmaspheric field‐aligned density irregularities.

Propagation of Very Oblique Chorus Waves Near a Plasmaspheric Plume Boundary

AbstractIn a case study using Van Allen Probe B, we investigate chorus wave observations near the western edge of a plasmaspheric plume characterized by steep density gradients. Initially, wave vectors are oriented anti‐Earthward, but they become very oblique and eastward as the probe approaches the plume boundary. Treating the plume boundary as an azimuthal density gradient, ray tracing can reproduce the observed wave vector directions. Ray tracing shows that the azimuthal density gradient strongly inclines the wave vectors eastward. Consequently, waves are reflected upon reaching the Gendrin angle and cannot enter the plume. We establish an analytical criterion for the azimuthal density enhancement, determining the condition for chorus waves to enter plumes near the equatorial region. Our results partly explain the oblique chorus near plumes observed by Hartley, Chen et al. (2022, https://doi.org/10.1029/2022GL098710), offering insight into wave‐particle interactions by chorus waves with the influence of azimuthal density structures.

Characteristics and Occurrence of Magnetosonic Waves in Plasmaspheric Plumes

AbstractMagnetosonic waves, or equatorial noise, are whistler‐mode emissions distributed near the Earth's magnetic equator between proton cyclotron frequency and lower hybrid resonance frequency. Their origin and characteristics inside and outside the plasmasphere have been investigated due to their potential role in scattering energetic electrons and protons. However, their characteristics in plasmaspheric plumes remained undocumented. This study, for the first time, statistically investigated magnetosonic waves in the plasmaspheric plumes based on the entire mission period (2012–2019) of Van Allen Probes A and B. Results showed that the occurrence rate of magnetosonic waves in plumes was 25%, with an average amplitude and wave normal angles of 44 pT and 84°–88°, respectively. Increased geomagnetic activity enhanced its amplitude and ratio of plasma frequency to electron cyclotron frequency. Approximately 78% of selected magnetosonic wave events were simultaneously observed with plasmaspheric hiss that is most effective in scattering electrons in the plume.

The Relation Among the Ring Current, Subauroral Polarization Stream, and the Geospace Plume: MAGE Simulation of the 31 March 2001 Super Storm

AbstractThe 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 31 March 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 (subauroral polarization streams (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.

Van Allen Probes Observations of a Three‐Dimensional Field Line Resonance at a Plasmaspheric Plume

AbstractField Line Resonances (FLRs) are a critical component in Earth's magnetospheric dynamics, associated with the transfer of energy between Ultra Low Frequency waves and local plasma populations. In this study we investigate how the polarisation of FLRs are impacted by cold plasma density distributions during geomagnetic storms. We present an analysis of Van Allen Probe A observations, where the spacecraft traversed a storm time plasmaspheric plume. We show that the polarisation of the FLR is significantly altered at the sharp azimuthal density gradient of the plume boundary, where the polarisation is intermediate with significant poloidal and toroidal components. These signatures are consistent with magnetohydrodynamic modeling results, providing the first observational evidence of a 3D FLR associated with a plume in Earth's magnetosphere. These results demonstrate the importance of cold plasma in controlling wave dynamics in the magnetosphere, and have important implications for wave‐particle interactions at a range of energies.

MMS Observations of Warm‐Ion (E < 100 eV) Heating Inside Plasmaspheric Plumes

AbstractNear‐Earth plasma surges sunward during enhanced magnetospheric convection (driven by dayside magnetic reconnection) to form a pathway feature called a plasmaspheric plume. This study uses Magnetospheric Multiscale (MMS) observations to investigate the heating of warm ions (H+ and He+) inside plumes. We identify 287 plume events using targeted in‐situ‐observational criteria and plasmapause test particle simulations. One plume‐crossing event by MMS shows that the scalar temperatures of warm He+ increase from ∼10 to ∼40 eV during simultaneous observations of helium‐band electromagnetic ion cyclotron (EMIC) waves, while H+ temperature is almost constant. Next, we analyze all individual observations to investigate warm‐ion heating and its possible association with EMIC waves. The statistical results show that EMIC waves associated with the plume have left‐hand polarizations and small normal angles and the temperatures of warm He+ are always higher than those of warm H+. Also, the minimum resonant energies for H+ are mostly above 100 eV, whereas 17% of warm He+ observations show that they can interact with the H+‐band EMIC waves via cyclotron resonance. These observations suggest that while EMIC waves play a role, there is an unknown mechanism for warm‐ion heating inside the plume that requires more investigation.

Effects of Cold Plasma on the Excitation of Internally Driven ULF Waves by Ring Current Ions Based On the Magnetosphere‐Ionosphere Coupled Model

AbstractInternally driven Pc4‐5 waves are excited in the plasmaspheric drainage plume (PDP) and near the plasmapause. The excitation of ultralow frequency (ULF) waves was investigated by using the magnetosphere‐ionosphere coupled model between Geospace Environment Modeling System for Integrated Studies‐Ring Current (GEMSIS‐RC) and GEMSIS‐POTential solver (GEMSIS‐POT). In order to investigate the effects of cold plasma on the wave excitation, the simulation code to describe the dynamics of cold plasma was included in the model. The model can reproduce the shrink of the plasmasphere on the nightside and the formation of the PDP on the dayside. First, fundamental Pc5 waves are excited through the drift resonance on the dayside. The waves are caused by positive energy gradient of ion phase space density (PSD) at 50–130 keV. Second harmonic waves (drift‐bounce resonance) are generated outside the plasmapause. These two types of ULF waves are also seen in the case of constant density. Unlike the case of constant density, localized eastward propagating Pc4 waves (drift resonance) are seen on the dawnside associated with the azimuthal density gradient. The azimuthal wave number of Pc4 waves is about 70 and anti‐earthward gradient of PSD about 10 keV contributes to wave growth. We also detect fundamental Pc4‐5 waves near the plasmapause on the nightside in the drift resonance with 100–150 keV ions. Simulation results suggest that the plasmapause has an effect to sustain the excitation of Pc4‐5 ULF wave through the drift resonance.

Deep learning model of hiss waves in the plasmasphere and plumes and their effects on radiation belt electrons

Hiss waves play an important role in removing energetic electrons from Earth’s radiation belts by precipitating them into the upper atmosphere. Compared to plasmaspheric hiss that has been studied extensively, the evolution and effects of plume hiss are less understood due to the challenge of obtaining their global observations at high cadence. In this study, we use a neural network approach to model the global evolution of both the total electron density and the hiss wave amplitudes in the plasmasphere and plume. After describing the model development, we apply the model to a storm event that occurred on 14 May 2019 and find that the hiss wave amplitude first increased at dawn and then shifted towards dusk, where it was further excited within a narrow region of high density, namely, a plasmaspheric plume. During the recovery phase of the storm, the plume rotated and wrapped around Earth, while the hiss wave amplitude decayed quickly over the nightside. Moreover, we simulated the overall energetic electron evolution during this storm event, and the simulated flux decay rate agrees well with the observations. By separating the modeled plasmaspheric and plume hiss waves, we quantified the effect of plume hiss on energetic electron dynamics. Our simulation demonstrates that, under relatively quiet geomagnetic conditions, the region with plume hiss can vary from L = 4 to 6 and can account for up to an 80% decrease in electron fluxes at hundreds of keV at L > 4 over 3 days. This study highlights the importance of including the dynamic hiss distribution in future simulations of radiation belt electron dynamics.

Filtering of Magnetosonic Waves by Mesoscale Plasmaspheric Density Interfaces

AbstractMagnetosonic waves inside and outside the plasmasphere differ statistically in occurrence rate, frequency, and intensity. How the density interface separates magnetosonic waves inside and outside the plasmasphere remains not fully understood. Here we report an experimental test made with the Van Allen Probes mission from the plasmaspheric plume through the low‐density channel to the plasmaspheric core. Our linear instability analysis and two‐dimensional full‐wave modeling support that the magnetosonic waves propagate from elsewhere to the channel, undergo reflection and transmission at the flanking plasmaspheric density interfaces and eventually exhibit drastic differences in intensity and frequency coverage between neighboring regions. Such a mesoscale (tens of wavelength wide) interface with a strong refractive index gradient allows the transformation of incident waves to surface waves and consequently filters waves in both frequency and orientation. This unexpected filtering pattern could commonly occur at the plasmaspheric boundary and eventually affect the global distribution of magnetosonic waves.

Observations of Time-Domain Structures in the Plasmaspheric Plume by Van Allen Probes

Time-domain structures (TDS), manifested as ≥ 1 ms pulses with significant parallel electric fields, play an important role in accelerating electrons in the field-aligned direction. These precipitated electrons contribute to the formation of aurora. In this study, we present observations of time-domain structures that occurred in the plasmaspheric plumes at the post-midnight to dawn sector. The close correlation between TDS and plasmaspheric plumes implies that the generation of TDS might be modulated by plasma density. During the wave occurrence, protons with an energy level below 1 keV show the enhanced field-aligned pitch-angle distributions, and the electron fluxes with the energies ranging from tens to hundreds of eV are also significantly enhanced. The correlation between TDS and scattered particles indicates the importance of including time-domain structures in future studies of radiation belt dynamics.

Width of plasmaspheric plumes related to the level of geomagnetic storm intensity

Abstract. The plume is a plasma region in the magnetosphere that is detached from the main plasmasphere. It significantly contributes to the dynamic processes in both the inner and outer magnetosphere. In this paper, using Van Allen Probe A (VAP-A), the correlation between plume width and the level of geomagnetic storm intensity is studied. First, through the statistical analysis of all potential plume events, we find that there is almost no correlation between plume width and the level of geomagnetic storm intensity. However, for the plumes in the recovery phase after improved sifting, it seems that there is a negative correlation between the plume width and the absolute value of minimum Dst during a storm. Utilizing test particle simulations, we study the dynamic evolution patterns of plumes during two geomagnetic storms. The simulated structures of the two plasmaspheric plumes are roughly consistent with the structures observed by the Van Allen Probe A. This result suggests that the plasmaspheric particles escape quickly during intense geomagnetic storms, causing the width of the plume to be relatively narrow during the recovery phase of intense geomagnetic storms. These results are helpful for understanding the dynamic evolution of the plasmasphere and plume during geomagnetic storms.

Nightside Plasmaspheric Plume‐To‐Core Migration of Whistler‐Mode Hiss Waves

AbstractWhistler‐mode hiss waves play an important role in the radiation belt electron depletion. Whether the hiss waves with significant differences in amplitude and propagation direction within the plasmaspheric core and plume are related to each other remains unclear. We here show that the plasmaspheric plume facilitates the energy conversion from energetic electrons to hiss waves and then guides hiss waves into the plasmaspheric core. Three ground and space missions captured the initial formation and subsequent rotation of the plasmaspheric plume in the noon‐dusk‐midnight sector following a strong substorm. The observed hiss waves in the nightside plasmaspheric plume and core propagated oppositely but highly correlated with each other at a time lag of 4–10 s. The linear instability of energetic electrons in the plasmaspheric plume qualitatively explains the frequency‐dependence of hiss waves, and the ray‐tracing modeling reproduces the propagation direction and timing of hiss waves.

Analysis of Electron Precipitation and Ionospheric Density Enhancements Due To Hiss Using Incoherent Scatter Radar and Arase Observations

AbstractPlasmaspheric hiss can cause energetic electron precipitation from the magnetosphere to the Earth's upper atmosphere and affect the ionospheric electron density profiles. In this study, we use Arase satellite measurements in the dayside plasmasphere to model the electron precipitation and the resultant ionospheric response, and compare the results to the electron density measured by the Poker Flat Incoherent Scatter Radar (PFISR). We analyzed two close conjunction events between Arase and PFISR at L ∼ 6 in the afternoon sector, when Arase was in the outer plasmasphere and traveled into the plasmaspheric plumes. Modest or strong hiss waves were observed with amplitudes higher than 50 pT during both events. Quasilinear modeling suggests that the hiss waves could cause intense electron precipitation ranging from several keV to several hundred keV energies. The electron density profiles at 60–90 km modeled by the Boulder Electron Radiation to Ionization (BERI) model suggest significant electron density enhancements due to the precipitating electrons. PFISR simultaneously observed electron density enhancements during both events, and provided evidence for the electron precipitation at altitudes down to <70 km. The temporal modulation of hiss caused the modulated density profiles in BERI modeling, but was not evident in PFISR observations. The modeled altitude profiles of the perturbed electron density overall agree with PFISR observation. At altitudes below 75 km, the modeled electron densities are lower than the observation, suggesting additional high energy electron precipitation possibly due to low frequency (<50 Hz) waves or hiss wave powers ducted to high latitudes.

Simulation of Cold Ion Transport Originating From the SED Plume Into Dayside Magnetosphere

AbstractIn this study, based on the Dynamic‐Kinetic Fluid (DyFK) model, we conduct simulations on the field‐aligned transport of cold ions (<1 eV) within three independent closed flux tubes from different starting points (L = 3.0 Re, L = 3.122 Re and L = 3.5 Re, respectively) during the 2015 St. Patrick's Day storm. These flux tubes magnetically connect the plasmaspheric plume with the ionospheric Storm Enhanced Density (SED) plume but drift toward the dayside magnetopause under E×B effects. Meanwhile, we can obtain the density variations of three ions species (H+, O+, and He+, respectively) around the flux tubes' apex (at the magnetic equator) as a function of the L shell. The simulations present the temporal evolution of cold plasma along these drifting flux tubes. We found that with increasing initial L shell location of the flux tube, there are more ionospheric cold light ions (H+ and He+) flowing into the equatorial region while the inflows of cold heavy ions (O+) toward the equator decrease. As the simulated flux tube drifts toward dayside magnetopause from the main plasmasphere (L = 3.0 Re), the SED sourced heavy ions pile up near the magnetic equator at low L shells (L < 4.0 Re) due to gravitational effects, while the light ions rapidly reach density equilibrium along the flux tube. With the flux tube drifting beyond L > 4.0 Re, the piled‐up cold heavy ions will later transport into the magnetic equatorial region and furnish the dayside magnetosphere, demonstrating that the SED is another supplier of magnetospheric cold heavy ions (O+).

Statistical study and corresponding evolution of plasmaspheric plumes under different levels of geomagnetic storms

Abstract. Using observations of Van Allen Probes, we present a statistical study of plasmaspheric plumes in the inner magnetosphere. Plasmaspheric plumes tend to occur during the recovery phase of geomagnetic storms. Furthermore, the results imply that the occurrence rate of observed plasmaspheric plume in the inner magnetosphere is larger during stronger geomagnetic activity. This statistical result is different from the observations of the Cluster satellite with much higher L shells in most orbital periods, which suggests that the plasmaspheric plume near the magnetopause tends to be observed during moderate geomagnetic activity (Lee et al., 2016). In the following, the dynamic evolutions of plasmaspheric plumes during a moderate geomagnetic storm in February 2013 and a strong geomagnetic storm in May 2013 are simulated through group test particle simulation. It is obvious that the plasmaspheric particles drift out on open convection paths due to sunward convection during both geomagnetic storms. It seems that the outer plasmaspheric particles exhaust the energy available to them sooner, and the plasmasphere shrinks faster during strong geomagnetic storms. As a result, the longitudinal width of the plume is narrower, and the plume is limited to lower L shells during the recovery phase of strong geomagnetic storm. The simulated evolutions may provide a possible interpretation for the occurrence rates: Van Allen Probes tend to observe plumes during stronger geomagnetic storms, and the Cluster satellite with higher L shells tends to observe plumes during moderate geomagnetic storms.

Multi‐Scale Density Structures in the Plasmaspheric Plume During a Geomagnetic Storm

AbstractEvolution of large‐scale and fine‐scale plasmaspheric plume density structures was examined using space‐ground coordinated observations of a plume during the 7–8 September 2015 storm. The large‐scale plasmaspheric plume density at Van Allen Probes A was roughly proportional to the total electron content (TEC) along the satellite footprint, indicating that TEC distribution represents the large‐scale plume density distribution in the magnetosphere. The plasmaspheric plume contained fine‐scale density structures and subauroral polarization streams (SAPS) velocity fluctuations. High‐resolution TEC data support the interpretation that the fine‐scale plume structures were blobs with ∼300 km size and ∼500–800 m/s in the ionosphere (∼3,000 km size and ∼5–8 km/s speed in the magnetosphere), emerging at the plume base and drifting to the plume. The short‐baseline Global Navigation Satellite System receivers detected smaller‐scale (∼10 km in the ionosphere, ∼100 km in the magnetosphere) TEC gradients and their sunward drift. Fine‐scale density structures were associated with enhanced phase scintillation index. Velocity fluctuations were found to be spatial structures of fine‐scale SAPS flows that drifted sunward with density irregularities down to ∼10 s of meter‐scale. Fine‐scale density structures followed a power law with a slope of ∼−5/3, and smaller‐scale density structures developed slower than the larger‐scale structures. We suggest that turbulent SAPS flows created fine‐scale density structures and their cascading to smaller scales. We also found that the plume fine‐scale density structures were associated with whistler‐mode intensity modulation, and localized electron precipitation in the plume. Structured precipitation in the plume may contribute to ionospheric heating, SAPS velocity reduction, and conductance enhancements.

Relation of the Plasmapause to the Midlatitude Ionospheric Trough, the Sub‐Auroral Temperature Enhancement and the Distribution of Small‐Scale Field Aligned Currents as Observed in the Magnetosphere by THEMIS, RBSP, and Arase, and in the Topside Ionosphere by Swarm

AbstractThe relation between the plasmapause (PP) and various ionospheric phenomena, such as the midlatitude ionospheric trough (MIT) has been studied for decades. More recently, it was found that the equatorward boundary of small‐scale field‐aligned currents (SSB) and the PP are also closely coupled. In spite of prolonged efforts many details of these relationships, as well as the mechanisms responsible for them remain poorly understood. ESA's Swarm mission in conjunction with magnetospheric missions (RBSP, Arase, and THEMIS) provides an unprecedented opportunity to study these relationships on a global scale and over an extended period. Swarm delivers observations of MIT, the associated sub‐auroral electron temperature enhancement (SETE), as well as SSB, while PP crossings can be inferred from in‐situ magnetospheric electron density measurements. In this study, we use 7 years of Swarm observations and PP positions from 2014 to 2017 to address some of the open questions. We confirm that MIT/SETE and PP are directly coupled, however only in the nighttime. Their correlation remains high after post‐dawn, however, with an increasing, MLT‐dependent time lag. Afternoon MIT observations were found conjugated with a plasmaspheric plume. The correlation between SSB and PP is also high and they intersect each other near MLT midnight. Our results confirm the scenario that the PP is formed on the night side, and propagates to the dayside by co‐rotating with the Earth and suggest that the plasma is transported from the depleted ionospheric/dense plasmaspheric stagnation region also westward/sunward forming the afternoon MIT/narrow plumes, respectively.