Small-scale Field-aligned Currents Research Articles

Small-scale Field-aligned Currents in the Magnetopause Boundary Layer

Based on high-resolution measurements from the Magnetospheric Multiscale mission from 2015 May to 2018 June, we statistically investigate the properties of small-scale field-aligned currents (SFACs) in the magnetopause boundary layer. A total of 2235 SFACs are successfully identified. The durations of SFACs mainly fall between 0.2 and 0.3 s. Over 90% of SFACs have a width of less than 1 ion inertia length and are primarily distributed from 5 to 25 electron inertia lengths, implying that the SFACs belong to the kinetic-scale current layer. The main carriers of SFACs are electrons, and over 70% of SFACs exhibit net energy dissipation (i.e., J · E ′ > 0) with the majority of energy dissipation taking place in the parallel direction. SFACs are widely distributed spatially, and the occurrence rate of SFACs is higher in the boundary layer closer to the magnetosphere. Additionally, less than half of the total SFACs are identified in well-known structures, including the magnetic reconnection region, flux transfer event, Kelvin–Helmholtz vortex, and exhaust region, and 54% of the SFACs are in the “others” unknown structures. These results improve our comprehension of the current system at the magnetopause and the roles of SFACs in the coupling between the solar wind and magnetosphere.

Small‐Scale Field‐Aligned Currents of Intense Amplitude Resolved by the Swarm Satellites

AbstractIn this study we used the Level‐2 product of field‐aligned currents (FACs) from the Swarm satellites, to check the distribution characteristics of small‐scale FACs (SSFACs) of intense amplitude. Data applied covers 9 years from December 2013 to April 2023. Based on the statistical analysis on the amplitude, the SSFACs in this study is defined with amplitude larger than 20 μA/m2, which is also by two orders larger than the well‐known large‐scale R1 and R2 FACs (about 0.2 μA/m2). Such an intense amplitude indicates that it should play an important role in the magnetosphere‐ionosphere coupling. The location of the SSFACs observed is general between 60°∼80° and −80°∼−60° magnetic latitude, which is coincidently inside the auroral oval. The occurrence of the SSFACs depends on both solar activity and geomagnetic activity, and the influence of geomagnetic activity is more important than that of solar activity. By further checking the simultaneous in situ plasma density measured by Swarm, we find that the SSFACs are always associated with clear plasma density fluctuations. This suggests that the SSFACs play an important role for causing the small‐scale plasma density irregularities at auroral latitude.

Correlation analysis of field-aligned currents from the magnetic measurements of GRACE follow-on mission

In this study we performed a detailed analysis on the scale-size of field-aligned currents (FACs) at auroral latitudes, using the well-calibrated magnetic data from the non-dedicated magnetic field mission, Gravity Recovery and Climate Experiment Follow-On (GRACE-FO). With two spacecraft following each other, the GRACE-FO provides a good opportunity to identify the variation of FACs with different scale lengths. The results show that the auroral FACs can be classified into two groups: the small-scale ones, shorter than some tens of kilometers, dominated by kinetic Alfvén waves, are quite dynamic; and the large-scale ones, typically larger than 150 km, can be considered as quasi-static and persist longer than 1 min. The GRACE-FO observations also reveal that the small-scale FACs at the same location sometimes can persist over 25 s, e.g., around dusk and dawn hours, which is longer than the typical persistent period (10 s) of kinetic Alfvén waves as earlier reported. The FAC structures show clear magnetic local time dependence, with higher correlations between the spacecraft around dusk and dawn hours; lower correlations are found around midnight and lowest correlations around noon, implying that the small-scale FACs most frequently appear at the noon cusp region. Slightly better correlations of FACs between two spacecraft are found during local summer, and such seasonal dependence is dominated by the correlations of small-scale FACs at noon. However, further analysis shows that the small-scale FACs at noon have largest occurrence and intensity during local summer, which reveals that when interpreting the cross-correlation analysis the intensity of FACs needs to be taken into account.Graphical

Swarm field-aligned currents during a severe magnetic storm of September 2017

Abstract. Swarm satellite observations are used to characterize the extreme behavior of large- and small-scale field-aligned currents (FACs) during the severe magnetic storm of September 2017. Evolutions of the current intensities and the equatorward displacement of FACs are analyzed while the satellites cross the pre-midnight, pre-noon, dusk and dawn sectors in both hemispheres. The equatorward boundaries of FACs mainly follow the dynamics of the ring current as monitored in terms of the SYM-H index. The minimum latitude of the FAC boundaries is limited to 50∘ magnetic latitude (MLat). The FAC densities are very variable and may increase dramatically, especially in the nightside ionosphere during the storm-time substorms. At the peak of substorms, the average FAC densities reach >3 µA m−2. The dawn–dusk asymmetry is manifested in the enhanced dusk-side R2 FACs in both hemispheres. In the 1 Hz data filamentary high-density structures are always observed. In the pre-noon sector, the bipolar structures (7.5 km width FACs of opposite polarities adjacent to each other) dominate, while at the other local times the upward and downward FACs tend to be latitudinally separated. The most intense small-scale FACs, up to ∼80 µA m−2, are observed just in the post-midnight sector. Simultaneous magnetic and plasma perturbations indicate that this structure is likely a current system of a mesoscale auroral arc.

Quantifying the relationship between the plasmapause and the inner boundary of small-scale field-aligned currents, as deduced from Swarm observations

Abstract. This paper presents a statistical study of the equatorward boundary of small-scale field-aligned currents (SSFACs) and investigates the relation between this boundary and the plasmapause (PP). The PP data used for validation were derived from in situ electron density observations of NASA's Van Allen Probes. We confirmed the findings of a previous study by the same authors obtained from the observations of the CHAMP satellite SSFAC and the NASA IMAGE satellite PP detections, namely that the two boundaries respond similarly to changes in geomagnetic activity, and they are closely located in the near midnight MLT sector, suggesting a dynamic linkage. Dayside PP correlates with the delayed time history of the SSFAC boundary. We interpreted this behaviour as a direct consequence of co-rotation: the new PP, formed on the night side, propagates to the dayside by rotating with Earth. This finding paves the way toward an efficient PP monitoring tool based on an SSFAC index derived from vector magnetic field observations at low-Earth orbit. Keywords. Magnetospheric physics (plasmasphere)

High‐Latitude Neutral Density Structures Investigated by Utilizing Multi‐Instrument Satellite Data and NRLMSISE‐00 Simulations

AbstractThis study investigates various types of neutral density features developed in the cusp region during magnetically active and quiet times. Multi‐instrument Challenging Minisatellite Payload data provide neutral density, electron temperature, neutral wind speed, and small‐scale field‐aligned current (SS‐FAC) values. Gravity Recovery and Climate Experiment neutral density data are also employed. During active times, cusp densities or density spikes appeared with their underlying flow channels (FCs) and enhanced SS‐FACs implying upwelling, fueled by Joule heating, within/above FCs. Both the moderate nightside cusp enhancements under disturbed conditions and the minor dayside cusp enhancements under quiet conditions developed without any underlying FC and enhanced SS‐FACs implying the role of particle precipitation in their development. Observations demonstrate the relations of FCs, density spikes, and upwelling‐related divergent flows and their connections to the underlying (1) dayside magnetopause reconnection depositing magnetospheric energy into the high‐latitude region and (2) Joule heating‐driven disturbance dynamo effects. Results provide observational evidence that the moderate nightside cusp enhancements and the minor dayside cusp enhancements detected developed due to direct heating by weak particle precipitation. Chemical compositions related to the dayside density spike and low cusp densities are modeled by Naval Research Laboratory Mass Spectrometer Incoherent Scatter Radar Extended 2000. Modeled composition outputs for the dayside density spike's plasma environment depict some characteristic upwelling signatures. Oppositely, in the case of low dayside cusp densities, composition outputs show opposite characteristics due to the absence of upwelling.

Magnetic ripples observed by Swarm satellites and their enhancement during typhoon activity

The Swarm satellites observed small-amplitude (0.1–5 nT) magnetic fluctuations perpendicular to the geomagnetic field. These so-called magnetic ripples (MRs) have a period of around a few tens of seconds along the satellite orbit in the topside ionosphere at middle and low latitudes. They are spatial structures from small-scale field-aligned currents. We investigated the following three characteristics of the MRs. First, we used Swarm observations to confirm their basic characteristics obtained from the Challenging Minisatellite Payload satellite. That is, the global distribution of the average MR amplitudes has clear geographic, seasonal, and local time dependence that is highly correlated with ionospheric conductivities. Second, we found that the average amplitudes of the MRs derived from the Swarm-B satellite, which flies at a ~50 km higher altitude, are slightly smaller than those of the Swarm-A and Swarm-C. This difference suggests that the location of the origin of MRs is below ~460 km altitude, i.e., not in the magnetosphere. Last, to provide evidence of correlation between the MRs and meteorological phenomena, we performed statistical and event analyses with typhoon track data, which are a source of acoustic and gravity waves. The data from 54 typhoons during the period from November 26, 2013, to July 31, 2016, were used for statistical analysis. The results show that the average amplitudes of the MRs during typhoon activity on the dawn, dusk, and night sides are larger than those during non-typhoon conditions. Event analyses indicate amplitude enhancements of the MRs around typhoons, and the latitude of the enhancement migrated with the typhoon. These analyses indicate that typhoon activity is correlated with MR activity and that cumulus convection activity other than typhoons may also affect MR amplitudes.Graphical abstract.

Investigating the polar ionosphere during the development of neutral density enhancements on 24–25 September 2000

AbstractWe focus on the well‐known northern daytime neutral density spikes detected by CHAMP on 25 September 2000 and related coupled magnetospheric‐ionospheric‐thermospheric processes. We investigate the underlying magnetic events and resultant thermospheric variations plus the state of the ionospheric polar region by employing multi‐instrument CHAMP and DMSP data. Results show the unfolding of a weak (SYM‐HMin ≈ −27 nT; ~0345 UT) magnetic storm during which these northern density spikes occurred. Some smaller southern daytime density spikes were also detected prior to this storm on the previous day. All these density spikes were detected in or near polar convection flow channels (FCs). Each FC was characterized by strong antisunward zonal ion drifts that excited the zonal and meridional neutral winds leaving the signature of FC in the CHAMP neutral wind measurements and thus providing direct observational evidence of FC underlying the density spike. Additional to the small‐scale field‐aligned current (SS‐FAC) filaments, the sudden intensifications of ionospheric closure current in the FC fueled the thermosphere and contributed to the development of upwelling and density spike. Some smaller density increases occurred due to the weak intensification of ionospheric closure currents. Equatorward (poleward) directed meridional neutral winds strengthened (weakened) the density spike by moving the neutral density up and along (down and against) the upwelling fueled by the ionospheric closure current and SS‐FAC filaments.

Transient, small-scale field-aligned currents in the plasma sheet boundary layer during storm time substorms.

We report on field‐aligned current observations by the four Magnetospheric Multiscale (MMS) spacecraft near the plasma sheet boundary layer (PSBL) during two major substorms on 23 June 2015. Small‐scale field‐aligned currents were found embedded in fluctuating PSBL flux tubes near the separatrix region. We resolve, for the first time, short‐lived earthward (downward) intense field‐aligned current sheets with thicknesses of a few tens of kilometers, which are well below the ion scale, on flux tubes moving equatorward/earthward during outward plasma sheet expansion. They coincide with upward field‐aligned electron beams with energies of a few hundred eV. These electrons are most likely due to acceleration associated with a reconnection jet or high‐energy ion beam‐produced disturbances. The observations highlight coupling of multiscale processes in PSBL as a consequence of magnetotail reconnection.

Confirmation of existence of the small-scale field-aligned currents in middle and low latitudes and an estimate of time scale of their temporal variation

The magnetic data obtained by the SWARM (the Earth's Magnetic Field and Environment Explorers) satellites in middle or low latitudes during the initial 2 months after launch were analyzed, when they flew nearly on the same orbit with variable time separation ranging from 5 to 100 s. It was confirmed that the small-scale magnetic fluctuations having period around 10–30 s are the manifestation of spatial structure of small-scale field-aligned currents along the orbits. From the statistical relation between correlation coefficients and two satellite separation in time, the typical time scale of temporal variation of the field-aligned current system is estimated to be around 200 s for meridional component and 340 s for zonal components of the magnetic fluctuations, respectively. Existence of shorter time scale around 30–50 s was also found. These results suggest that the main source of current generation is the acoustic mode of atmospheric gravity waves.

Climatology of zonal wind and large-scale FAC with respect to the density anomaly in the cusp region: seasonal, solar cycle, and IMF <i>B</i><sub><i>y</i></sub> dependence

Abstract. We investigate the relationship of the thermospheric density anomaly (ρrel) with the neutral zonal wind velocity (Uzonal), large-scale field-aligned current (FAC), small-scale FAC, and electron temperature (Te) using the superposed epoch analysis (SEA) method in the cusp region. The dependence of these variables on the sign of the interplanetary magnetic field (IMF) By component and local season is of particular interest. Also, the conditions that lead to larger relative density enhancements are investigated. Our results are based on CHAMP satellite data and OMNI online data of IMF for solar maximum (March 2002–March 2007) and minimum (March 2004–March 2009) conditions in the Northern Hemisphere. In the cusp region the SEA technique uses the time and location of the mass density anomaly peaks as reference parameters. On average, the amplitude of the relative density anomaly, ρrel, does not depend on the solar cycle phase, local season, and IMF By sign. Also, it is apparent that the amplitude of IMF By does not have a large influence on ρrel, while the negative IMF Bz amplitude prevailing about half an hour earlier is in good correlation with ρrel. Both the zonal wind velocity and the large-scale FAC (LSFAC) distribution exhibit a clear dependence on the IMF By sign. Uzonal is directed towards dawn for both positive and negative IMF By at all local seasons and for solar maximum and minimum conditions. There is a systematic imbalance between downward (upward) and upward (downward) large-scale FACs peaks equatorward and poleward of the reference point, respectively, for the IMF By+ (By−) case. Relative density enhancements appear halfway between region 1 and region 0 currents in closer proximity to the upward FAC region. FAC densities and mass density anomaly amplitudes are not well correlated, but it is apparent that there is a close spatial relationship between ρrel and LSFAC. At this point we cannot offer any simple functional relation between these two variables, because there seem to be additional quantities controlling this relation.

The relationship of thermospheric density anomaly with electron temperature, small-scale FAC, and ion up-flow in the cusp region, as observed by CHAMP and DMSP satellites

Abstract. We present in a statistical study a comparison of thermospheric mass density enhancements (ρrel) with electron temperature (Te), small-scale field-aligned currents (SSFACs), and vertical ion velocity (Vz) at high latitudes around noon magnetic local time (MLT). Satellite data from CHAMP (CHAllenging Minisatellite Payload) and DMSP (Defense Meteorological Satellite Program) sampling the Northern Hemisphere during the years 2002–2005 are used. In a first step we investigate the distribution of the measured quantities in a magnetic latitude (MLat) versus MLT frame. All considered variables exhibit prominent peak amplitudes in the cusp region. A superposed epoch analysis was performed to examine causal relationship between the quantities. The occurrence of a thermospheric relative mass density anomaly, ρrel >1.2, in the cusp region is defining an event. The location of the density peak is taken as a reference latitude (Δ MLat = 0°). Interestingly, all the considered quantities, SSFACs, Te, and Vz are co-located with the density anomaly. The amplitudes of the peaks exhibit different characters of seasonal variation. The average relative density enhancement of the more prominent density peaks considered in this study amounts to 1.33 during all seasons. As expected, SSFACs are largest in summer with average amplitudes equal to 2.56 μA m−2, decaying to 2.00 μA m−2 in winter. The event related enhancements of Te and Vz are both largest in winter (Δ Te =730 K, Vz =136 m s−1) and smallest in summer (Δ Te = 377 K, Vz = 57 m s−1. Based on the similarity of the seasonal behaviour we suggest a close relationship between these two quantities. A correlation analysis supports a linear relation with a high coefficient greater than or equal to 0.93, irrespective of season. Our preferred explanation is that dayside reconnection fuels Joule heating of the thermosphere causing air upwelling and at the same time heating of the electron gas that pulls up ions along affected flux tubes.

Geomagnetic response to solar and interplanetary disturbances

The space weather discipline involves different physical scenarios, which are characterised by very different physical conditions, ranging from the Sun to the terrestrial magnetosphere and ionosphere. Thanks to the great modelling effort made during the last years, a few Sun-to-ionosphere/thermosphere physics-based numerical codes have been developed. However, the success of the prediction is still far from achieving the desirable results and much more progress is needed. Some aspects involved in this progress concern both the technical progress (developing and validating tools to forecast, selecting the optimal parameters as inputs for the tools, improving accuracy in prediction with short lead time, etc.) and the scientific development, i.e., deeper understanding of the energy transfer process from the solar wind to the coupled magnetosphere-ionosphere-thermosphere system. The purpose of this paper is to collect the most relevant results related to these topics obtained during the COST Action ES0803. In an end-to-end forecasting scheme that uses an artificial neural network, we show that the forecasting results improve when gathering certain parameters, such as X-ray solar flares, Type II and/or Type IV radio emission and solar energetic particles enhancements as inputs for the algorithm. Regarding the solar wind-magnetosphere-ionosphere interaction topic, the geomagnetic responses at high and low latitudes are considered separately. At low latitudes, we present new insights into temporal evolution of the ring current, as seen by Burton’s equation, in both main and recovery phases of the storm. At high latitudes, the PCC index appears as an achievement in modelling the coupling between the upper atmosphere and the solar wind, with a great potential for forecasting purposes. We also address the important role of small-scale field-aligned currents in Joule heating of the ionosphere even under non-disturbed conditions. Our scientific results in the framework of the COST Action ES0803 cover the topics from the short-term solar-activity evolution, i.e., space weather, to the long-term evolution of relevant solar/heliospheric/magnetospheric parameters, i.e., space climate. On the timescales of the Hale and Gleissberg cycles (22- and 88-year cycle respectively) we can highlight that the trend of solar, heliospheric and geomagnetic parameters shows the solar origin of the widely discussed increase in geomagnetic activity in the last century.

Storm-time related mass density anomalies in the polar cap as observed by CHAMP

Abstract. Strong and localized thermospheric mass density events are observed in the polar cap region by the CHAMP satellites at about 400 km altitude during geomagnetic storms. During the 4 years considered (2002–2005) 29 storms with Dst<−100 nT occurred, in 90% of them polar cap density anomalies were detected. Based on the altogether 56 anomaly events a statistical analysis was performed. The anomalies are of medium scale (500–1500 km) and seem to have a short dwell-time (<1.5 h) in the polar cap. The relative density enhancement is found to range around 2 in both hemispheres. The peak density is in the Northern Hemisphere by a factor of 1.4 larger than in the southern. Also the number of detected events in the north is twice as large as that in the south (37 vs. 19). Mass density anomalies in the polar cap occur under all interplanetary magnetic field (IMF) directions. Numerous strong anomalies have been detected in positive and negative IMF Bz conditions when the magnetic field strength is above 5 nT. Rather few events occurred for small |Bz| (<5 nT) or for positive Bz combined with vanishing By. Some of the density anomalies are accompanied by intensive small-scale field-aligned currents (FACs). But about as many show no relation to FACs. If FACs are present there, the current density is believed to be correlated with the strength of the IMF Bz. Although this paper concentrates on the presentation of the observations, we show for one event that the ion outflow mechanism could be responsible for the mass density anomalies in the polar cap.

Excitation of Alfvén vortices in the ionosphere by the magnetospheric convection

We analyze conditions for excitation of ULF waves in the ionospheric Alfven resonator (IAR), taking into account the altitude-inhomogeneous profile of the magnetospheric convection velocity. This profile is formed as a result of interaction of the convective flow with the neutral atmosphere at altitudes 90–150 km. ULF waves comprise oblique Alfven waves, trapped into the IAR, and ionospheric drift waves, which are in resonance with them. These waves together form strongly anisotropic, closed current loops, whose scale along the magnetic field greatly exceeds their transverse scale, i.e., lz ≫ l⊥, and can be considered Alfven vortices. Within the framework of the proposed model of the ionosphere, we study the instability threshold and the amplitude growth rate of the Alfven vortices as functions of different parameters (wave vector k22A5, angle between the wave vector and the convection velocity, ratio of the Alfven-wave and Pedersen conductivities, etc.). Some estimates are given in application to the observed small-scale field-aligned currents in the auroral ionosphere.

Are small-scale field-aligned currents and magnetosheath-like particle precipitation signatures of the same low-altitude cusp?

We examined some 75 observations from the low-altitude Earth orbiting DMSP, Ørsted and CHAMP satellites which were taken in the region of the nominal cusp. Our objective was to determine whether the actually observed cusp locations as inferred from magnetosheath-like particle precipitation (“particle cusp”) and intense small-scale magnetic field variations (“current cusp”), respectively, were identical and were consistent with the statistically expected latitude of the cusp derived from a huge number of charged particle spectrograms (“statistical cusp”). The geocentric coordinates of the satellites were converted into AACGM coordinates, and the geomagnetic latitude of the cusp boundaries (as indicated by precipitating particles and small-scale field-aligned currents) set in relation to the IMF-B z dependent latitude of the equatorward boundary of the statistical cusp. We find that the actually observed latitude of the particle cusp matches well the statistically expected latitude while the current cusp appears to cover most of the statistical cusp and also a ≈1° wide section beyond the equatorward boundary of the statistical cusp. This leads us to suggest that intense small-scale field-aligned currents are generated in the cusp but also in the transition zone between the low-latitude boundary layer (LLBL) and the cusp, probably within both regimes, the cusp and the open LLBL. The small-scale field-aligned currents are possibly a consequence of turbulence and/or instabilities associated with the process of opening previously closed magnetospheric field lines and merging them with the interplanetary magnetic field.

Small-scale arcs and “Electrostatic Shocks”: Eigenmodes of transverse Alfvén wave-guide

A model is presented of the so called A-Shocks, i.e. ▪ longitudinal currents and perpendicular electric fields (‘Electrostatic Shocks’), associated with low-altitude particle acceleration. The two new elements of the model with respect to the previous ‘static’ and ‘Alfvén wave’ models are the transverse wave-guide for shear Alfvén waves (TAWG) and density dip in the center of the structure. The TAWG is a density depletion in the ‘cold’, β ⪡ m M , plasma at altitudes below ∼ 2 R E . A pair of small-scale field-aligned currents (FACs) is found to be the eigenmode of the TAWG. The n e -dip, yielding matching j ‖ and E ∥, is formed by the ion polarization current maintained by transverse motion with respect to the background plasma.

Structure of auroral zone phenomena from the data of meridional chains of stations: magnetic disturbances in the nighttime auroral zone and auroras

A new method of compulation of the equivalent currents using meridional chain stations' magnetic data is proposed to study the auroral electrojet structure. The correctness and resolving power of the method are estimated by test calculations. On the basis of computer simulation studies, it is shown that the method may be applied in practice when variations in the geomagnetic H-components are sufficiently larger than those in the D-component. Using the method, a fine structure of the westward electrojet was found. This structure is the same at two longitudinally separated meridians (in Scandinavia and the Kola peninsula) and seems to be associated with auroral features. The conclusion is made that the small-scale field-aligned and ionospheric currents with a width of less than 0.5 are not displayed in magnetic observations made on the ground against the effects of larger-scale structures.

Small‐scale field‐aligned currents observed by the Akebono (EXOS‐D) satellite

The EXOS‐D fluxgate magnetometer data obtained at 3000–10000 km altitude have shown that small‐scale field‐aligned currents always exist in large‐scale region 1, region 2, cusp and polar cap current systems. Assuming that these small‐scale field‐aligned currents have current sheet structure, the width of current sheet is estimated to be 5–20 km at ionospheric altitude. By comparing the magnetometer data with charged particle and high frequency plasma wave data simultaneously obtained from EXOS‐D, it is found that small‐scale currents have one‐to‐one correspondence with localized electron precipitation events characterized by flux enhancement over a wide energy range from 10 eV to several keV and broadband electrostatic bursts occasionally extending above local plasma frequencies or electron cyclotron frequencies.

Magnetic field observations on the Akebono (EXOS-D) satellite.

The Akebono (EXOS-D) satellite carries triaxial fluxgate and search coil magnetometers with sensors mounted on 5- and 3-m masts, respectively. The fluxgate magnetometer has four automatically switchable ranges from ±1024 to ±65536nT (full scale), and resolutions commensurate with a 16-bit A/D converter in each range (0.031 to 2nT). The rate of sampling is 32 vectors per second. The triaxial search coil magnetometer has a frequency response up to 800Hz. Signals in the frequency range higher than 100Hz are used for VLF plasma wave experiments (KIMURA et al., 1990), while signals less than 100Hz are used for magnetic field experiments.After the 3- and 5-m masts were extended on March 7 and 8, 1989, respectively, both the magnetometers are operating continuously. Intense small-scale field-aligned currents embedded in the large-scale field-aligned current system were always observed at 1-2 Re altitudes in all local time regions. The region 0 currents which flow in the poleward region adjacent to the region 1 currents were also frequently observed. The search coil magnetometer measured ion cyclotron waves at 1-2 Re altitudes near the equator.