Evolutions of equatorial ring current ions during a magnetic storm

In this paper, we present evolutions of the phase space density(PSD) spectra of ring current(RC) ions based on observations made by Van Allen Probe B during a geomagnetic storm on 23–24 August 2016. By analyzing PSD spectra ratios from the initial phase to the main phase of the storm, we find that during the main phase, RC ions with low magnetic moment μ values can penetrate deeper into the magnetosphere than can those with high μ values, and that the μ range of PSD enhancement meets the relationship: S(O^+) >S(He^+)>S(H^+). Based on simultaneously observed ULF waves, theoretical calculation suggests that the radial transport of RC ions into the deep inner magnetosphere is caused by drift-bounce resonance interactions, and the efficiency of these resonance interactions satisfies the relationship: η(O^+) > η(He^+) > η(H^+), leading to the differences in μ range of PSD enhancement for different RC ions. In the recovery phase,the observed decay rates for different RC ions meet the relationship: R(O^+) > R(He^+) > R(H^+), in accordance with previous theoretical calculations, i.e., the charge exchange lifetime of O^+ is shorter than those of H^+ and He^+.

The effect of non-storm time substorms on the ring current dynamics

During geomagnetically active times such as geomagnetic storms,large amounts of energy can be released into the Earth’s magnetosphere and change the ring current intensity.Previous studies showed that significant enhancement of the ring current was related to geomagnetic storms,while few studies have examined substorm effects on ring current dynamics.In this study,we examine the ring current variation during non-storm time(SYM-H>−50 nT)substorms,especially during super-substorms(AE>1000 nT).We perform a statistical analysis of ring current plasma pressure and number flux of various ion species under different substorm conditions,based on Van Allen Probe observations.The plasma pressure and ion fluxes of the ring current increased dramatically during supersubstorms,while little change was observed for substorms with AE<1000 nT.The results shown in this study indicate that a non-storm time super-substorm may also have a significant contribution to the ring current.

Effects of polarization-reversed electromagnetic ion cyclotron waves on the ring current dynamics

Electromagnetic ion cyclotron(EMIC)waves are widely believed to play an important role in influencing the radiation belt and ring current dynamics.Most studies have investigated the effects or characteristics of EMIC waves by assuming their left-handed polarization.However,recent studies have found that the reversal of polarization,which occurs at higher latitudes along the wave propagation path,can change the wave-induced pitch angle diffusion coefficients.Whether such a polarization reversal can influence the global ring current dynamics remains unknown.In this study,we investigate the ring current dynamics and proton precipitation loss in association with polarization-reversed EMIC waves by using the ring current-atmosphere interactions model(RAM).The results indicate that the polarization reversal of H-band EMIC waves can truly decrease the scattering rates of protons of 10 to 50 keV or>100 keV in comparison with the scenario in which the EMIC waves are considered purely left-handed polarized.Additionally,the global ring current intensity and proton precipitation may be slightly affected by the polarization reversal,especially during prestorm time and the recovery phase,but the effects are not large during the main phase.This is probably because the H-band EMIC waves contribute to the proton scattering loss primarily at E<10 keV,an energy range that is not strongly affected by the polarization reversal.

Prediction of Partial Ring Current Index Using LSTM Neural Network

The local time dependence of the geomagnetic disturbances during magnetic storms indicates the necessity of forecasting the localized magnetic storm indices.For the first time,we construct prediction models for the SuperMAG partial ring current indices(SMR-LT),with the advance time increasing from 1 h to 12 h by Long Short-Term Memory(LSTM)neural network.Generally,the prediction performance decreases with the advance time and is better for the SMR-06 index than for the SMR-00,SMR-12,and SMR-18 index.For the predictions with 12 h ahead,the correlation coefficient is 0.738,0.608,0.665,and 0.613,respectively.To avoid the over-represented effect of massive data during geomagnetic quiet periods,only the data during magnetic storms are used to train and test our models,and the improvement in prediction metrics increases with the advance time.For example,for predicting the storm-time SMR-06 index with 12 h ahead,the correlation coefficient and the prediction efficiency increases from 0.674 to 0.691,and from 0.349 to 0.455,respectively.The evaluation of the model performance for forecasting the storm intensity shows that the relative error for intense storms is usually less than the relative error for moderate storms.

The substorm current wedge and midnight sector partial ring current near substorm onset: A synthesis based on a magnetotail magnetic field geometry model

The Substorm Current Wedge （SCW） occurrence in the late growth and onset phases of substorms was proposed as the current system which disrupts cross-tail current by diverting it to the ionosphere. The closure current for the SCW originally was suggested to be the strong westward auroral electrojet （WEJ）. However, the SCW-WEJ system has no viable generator current. Similarly, the asymmetric or Partial Ring Current （PRC） increases in strength during the growth phase, and is sometimes associated with an enhanced Region 2 field-aligned current （FAC） closing to the ionosphere, but specifics of that closure have been lacking. Here we present a tmifying picture which includes the SCW post- and pre-midnight （AM and PM, respectively） currents and a generator current in the midnight portion of the PRC system, with these currents based upon a model of the nightside magnetotail magnetic geometry. That geometry consists of open north and south lobe regions surrounding a plasmasheet with two types of closed field line regions-stretched lines in the central part of the plasmasheet （SPS） and dipolar lines （DPS） between the low lati- tude boundary layer （LLBL） regions and the SPS. There is also an important plasmasheet transition region （TPS） in which the dipolar field near the plasmapause gradually transforms to stretched lines near the earthward edge of the SPS, and in which the midnight part of the PRC flows. We propose that our proposed near-onset current system consists of a central current which be- comes part of the midnight sector PRC and which is the generator, to which are linked two three-part current systems, one on the dawnside and one on the duskside. The three-part systems consist of up and down FACs closing as Pedersen currents in the iono- sphere. These 3-part systems are not activated until near-onset is reached, because of a lack of ionospheric conductivity in the appropriate locations where the Pedersen current closure occurs. The initial downward FAC of the 3-part dawnside system and the final upward FAC of the 3-part duskside system correspond to the AM and PM current segments, respectively, of the originally proposed SCW.

Ring current proton scattering by low-frequency magnetosonic waves

Magnetosonic (MS) waves are believed to have the ability to affect the dynamics of ring current protons both inside and outside the plasmasphere. However, previous studies have focused primarily on the effect of high-frequency MS waves (f > 20 Hz) on ring current protons. In this study, we investigate interactions between ring current protons and low-frequency MS waves (< 20 Hz) inside the plasmasphere. We find that low-frequency MS waves can effectively accelerate < 20 keV ring current protons on time scales from several hours to a day, and their scattering efficiency is comparable to that due to high-frequency MS waves (>20 Hz), from which we infer that omitting the effect of low-frequency MS waves will considerably underestimate proton depletion at middle pitch angles and proton enhancement at large pitch angles. Therefore, ring current proton modeling should take into account the effects of both low- and highfrequency MS waves.

Study on the local time asymmetry of the Earth's ring currents based on multiple low-Earth-orbit satellite magnetic observations

The azimuthal morphology of Earth's ring currents has consistently shown asymmetry during extreme space weather events at low latitudes,particularly during geomagnetic storms.A dawn-dusk pattern has been detected during the storm main phase through near-Earth and in-situ magnetic measurements.This asymmetry is believed to arise from asymmetric solar windmagnetosphere coupling and is linked to the closure of the ring current.Recent evidence has confirmed the existence of asymmetric ring currents during quiet times and the storm recovery phase.This phenomenon may be closely related to the evolution of ring currents,including plasma injection and decay processes.In this study,the local time asymmetry of the ring current is estimated using data from low-Earth-orbit Swarm and Macao Science Satellite-1(MSS-1)missions.Spherical harmonics models are developed to quantify the magnetic field of ring currents through external Gauss coefficients during both quiet periods and the storm recovery phase.Several features of dawn-dusk asymmetry are observed in various cases in different months.(1)The maximum difference in magnetic value across local time ranges from 3 to 10 nT,showing relative invariance compared with various Sym-H levels.(2)Stronger magnetic signals are detected at the premidnight sector during quiet times and at the afternoon sector during the storm recovery phase.(3)Magnetic perturbations remain at a lower level during the postmidnight and morning sectors.Although the pattern of local time asymmetry differs between quiet times and the recovery phase,dawn-dusk asymmetry remains the most pronounced feature,affecting the trapping and loss of charged particles in the inner magnetosphere.Combining Swarm and MSS-1 magnetic observations can enable convenient monitoring of the detailed azimuthal local time effects of the ring current at various disturbance levels in the future.

The causal sequence investigation of the ring current ion-flux increasing and the magnetotail ion injection during a major storm

Comprehensive records are available in ENA data of ring current activity recorded by the NUADU instrument aboard TC-2 on 15 May, 2005 during a major magnetic storm （which incorporated a series of substorms）. Ion fluxes at 4-min temporal resolution derived from ENA data in the energy ranges 50-81 and 81-158 keV are compared with in situ particle fluxes measured by the LANL-SOPA instruments aboard LANL-01, LANL-02, LANL-97, and LANL-84 （a series of geostationary satellites that encircle the equatorial plane at -6.6 RE）. Also, magnetic fields measured simultaneously by the magetometers aboard GOES-10 and GOES-12 （which are also geostationary satellites） are compared with the particle data. It is demonstrated that ion fluxes in the ring current were enhanced during geomagnetic field tailward stretching in the growth phases of substorms rather than after Earthward directed dipolarization events. This observation, which challenges the existing concept that ring current particles are injected Earthward from the magnetotail following dipolarization events, requires further investigation using a large number of magnetic storm events.

Identification of ring current proton precipitation driven by scattering of electromagnetic ion cyclotron waves

Among the most intense emissions in the Earth's magnetosphere,electromagnetic ion cyclotron(EMIC)waves are regarded as a critical candidate contributing to the precipitation losses of ring current protons,which however lacks direct multi-point observations to establish the underlying physical connection.Based upon a robust conjunction between the satellite pair of Van Allen Probe B and NOAA-19,we perform a detailed analysis to capture simultaneous enhancements of EMIC waves and ring current proton precipitation.By assuming that the ring current proton precipitation is mainly caused by EMIC wave scattering,we establish a physical model between the wave-driven proton diffusion and the ratio of precipitated-to-trapped proton count rates,which is subsequently applied to infer the intensity of EMIC waves required to cause the observed proton precipitation.Our simulations indicate that the model results of EMIC wave intensity,obtained using either the observed or empirical Gaussian wave frequency spectrum,are consistent with the wave observations,within a factor of 1.5.Our study therefore strongly supports the dominant contribution of EMIC waves to the ring current proton precipitation,and offers a valuable means to construct the global profile of EMIC wave intensity using low-altitude NOAA POES proton measurements,which generally have a broad L-shell coverage and high time resolution in favor of near-real-time conversion of the global EMIC wave distribution.

Ground magnetic characteristics of the storm-time ring current Asymmetry

Using the minute data of the H component of geomagnetic field from the 20°E magnetic meridian chain and the 30°N magnetic latitudinal chain, the temporal evolution characteristics of the equatorial ring current during the storm on November 7-10, 2004 are studied. It is indicated that the UT-MLT and UT-MLAT graphics extremely exhibit the local time distribution, latitudinal variation and temporal evo- lution of the H component. The results show: (1) The UT-MLT contour clearly shows the increasing of the H component mostly around noon during the initial phase, representing the geomagnetic effect from the magnetopause current system. During the main phase, most negative values of the H com- ponent appear around the dusk-side, indicating the dawn-dusk asymmetric distribution of the ring cur- rent. (2) The contour of UT-MLAT suggests the latitudinal variation of the H component decreasing with the enhancement of the latitudes during geomagnetic storm, which is in good agreement with the Dst index. The latitudinal variations provide a new sight for describing the temporal characteristics of the intensity of the storm-time ring current. (3) Both the contours of UT-MLT and UT-MLAT are useful to monitor the space-time distribution of the equatorial ring current.

Tilt of the ring current during the main phases of intense geomagnetic storms

Based on the data from the SuperMAG collaboration in 2000–2014, the magnetic latitude(MLAT) location of the ring current(RC) denoted by the MLAT of the maximum horizontal magnetic disturbance during the main phase of 67 intense geomagnetic storms(Dst ≤-100 nT) are derived. The results show that the maximum horizontal magnetic disturbance does not always occur in the magnetic equator, indicating that the RC might be tilted in the latitudinal direction during these storms. Specifically, the tilt of the RC near the day-night line is affected by the direction of solar wind. When the solar wind flows southward against the magnetic equatorial plane, the RC is more likely to show a dayside-lifted tilt. When the solar wind flows northward, the pattern is opposite. Tilts of the RC near the dawn-dusk line are also found in most of these storms. The location of the RC is mainly lifted in the dusk side and declined in the dawn side for positive IMF BY, while the tilt is reversed for negative IMF BY. A possible interpretation might be the IMF BY-related twisting of the geomagnetic field. Besides, the monthly averaged MLAT of the fitted RC also varies with seasons. It is shifted to the southern hemisphere in the northern summer and to the northern hemisphere in the northern winter, which might indicate that the RC is not centered on a single plane. Such a seasonal variation might be related to the angle between the solar wind and the magnetic equatorial plane.

Formation of the storm-time ring current

An extensive study of ring current injection and intensification of the storm-time symmetric ring current is conducted with three-dimensional (3-D) test particle trajectory calculations (TPTCs) in this paper. TPTCs reveal more accurately the process of ring current injection. The main results are the following: (1) an intense convection electric field can effec-tively energize and inject plasma sheet particles into ring current region within 1-3 h. (2) Injection ions often follow chaotic trajectories in non-adiabatic regions,which may have implications in storm and ring current physics. (3) The shielding electric field, which arises as a consequence of enhanced convection and co-exists with injection and convection electric field, leads the original open trajectories to change into closed ones, thus may play an important role in the formation of the symmetric ring current.

Latitudinal shift and tilt of the ring current during magnetic storms

The equatorial ring current (ERC) theory suggested that the distribution of global disturbed horizontal geomagnetic field only depends on the cosine of station’s latitude. However,we always observe a lar-ger ΔH at higher latitude stations than lower ones,implying that the ERC could tilt or/and shift with respect to the equatorial plane during intense storms. In this paper,we analyze 11 intense magnetic storms from 2000 to 2004,and introduce two configurational factors to characterize the topology of storm time ring current. The results show that ERC has occasionally deviated off equatorial plane with both tilt angle δt≈13°―25° and latitude shift δs≈0°―21.8°. The ground disturbed field distribution should be improved as ΔHk = ΔHmaxcos(k-δ ),which agree well with the geomagnetic observations.

Persistent current in a magnetized Rashba ring

We theoretically study the persistent currents flowing in a Rashba quantum ring subjected to the Rashba spinorbit interaction. By introducing uniform or nonuniform magnetization into the ring, we find that a nonzero persistent charge current circulates in the ring, which stems from the original equilibrium spin current due to the Rashba spinorbit interaction. Because of broken time reversal symmetry, the two oppositely flowing spin-up and spin-down charge currents of the equilibrium spin current are no longer equal, and so a net persistent charge current can flow in the system. It is also found that the persistent current can be modulated by the Fermi energy, the Rashba spin-orbit interaction strength and the magnetization in the ring. Moreover, the magnetization perpendicular to the ring plane can optimize the current. The persistent current flowing in the ring is a manifestation of the nonzero equilibrium spin current existing in the ring.

PERSISTENT CURRENT IN A ONE-DIMENSIONAL MESOSCOPIC RING WITH ELECTRON-PHONON INTERACTION IN THE LATTICE MODEL

A new non-perturbative method is used to discuss the persistent current in a one-dimensional mesoscopic ring threaded by a flux φ with electron-phonon interaction in the lattice model. The current is periodic in φ with a flux quantum φ 0 and the electron-phonon interaction suppresses the persistent current. By considering the contributions of many-phonon correlations, we could obtain more accurate results.

Current–phase relations of a ring-trapped Bose–Einstein condensate with a weak link

The current–phase relations of a ring-trapped Bose–Einstein condensate interrupted by a rotating rectangular barrier are extensively investigated with an analytical solution. A current–phase diagram, single and multi-valued relation, is presented with a rescaled barrier height and width. Our results show that the finite size makes the current–phase relation deviate a little bit from the cosine form for the soliton solution in the limit of a vanishing barrier, and the periodic boundary condition selects only the plane wave solution in the case of high barrier. The reason for multi-valued current–phase relation is given by investigating the behavior of soliton solution.

Oscillation of the spin-currents of cold atoms on a ring due to light-induced spin–orbit coupling

The evolution of two-component cold atoms on a ring with spin-orbit coupling has been studied analytically for the case with N noninteracting particles. Then, the effect of interaction is evaluated numerically via a two-body system. Two cases are considered： （i） Starting from a ground state the evolution is induced by a sudden change of the laser field, and （ii） the evolution starting from a superposition state. Oscillating persistent spin-currents have been found. A set of formulae have been derived to describe the period and amplitude of the oscillation. Based on these formulae the oscillation can be well controlled via adjusting the parameters of the laser beams. In particular, it is predicted that movable stripes might emerge on the ring.

Spin-polarization-dependent transport in a quantum dot array coupled with an Aharonov-Bohm ring

In this paper the quantum transport in a dot-array coupled with an Ahaxonov-Bohm （AB） ring is investigated via single-band tight-binding Hamiltonian. It is shown that the output spin current is a periodic function of the magnetic flux in the quantum unit Ф0. The resonance positions of the total transmission probability do not depend on the size of the AB ring but the electronic spectrum. Moreover, the persistent currents in the AB ring is also spin-polarization dependent and different from the isolated AB ring where the persistent current is independent of spin polarization.

Tunable Kondo Effect of a Three-Terminal Transport Quantum Dot Embedded in an Aharonov-Bohm Ring

We theoretically investigate the Kondo effect of a three-terminal transport quantum dot （QD） embedded in an Aharonov-Bohm ring in the Kondo regime by means of the one-impurity Anderson Hamiltonian. The Hamiltonian is solved by means of the slave-boson mean-field theory. We find that in this system, the Kondo effect depends sensitively oil the parity and size of the ring; the Kondo screening cloud can be tuned by tuning the coupling strength of the reservoir-dot. Thus this model might be a candidate for future device applications.