Convection Electric Field Model Research Articles

Formation of the Low‐Energy “Finger” Ion Spectral Structure Near the Inner Edge of the Plasma Sheet

AbstractWe present a case study of the H+, He+, and O+ low‐energy “finger” structure observed by the Van Allen Probe A Helium, Oxygen, Proton, and Electron (HOPE) spectrometer on 26 October 2016. This structure, whose characteristic energy is from approximately tens of eV to a few keV, looks like a “finger” that is rich in O+ and He+, faint in H+ on an energy‐time spectrogram. By using the Space Weather Modeling Framework (SWMF) and Weimer05 electric fields, combined with a dipole or more self‐consistent magnetohydrodynamic (MHD) magnetic field, backward tracing of O+ reveals that the structure is formed by ions with a long drift time from the plasma sheet during the magnetic storm main phase to the inner region with trajectories dominated by eastward drift motion, and the formation depends on the convection electric field model. The heavy ion dominance of the feature is explained by charge exchange losses along the long slow drift paths.

Validity Study of the Swarm Horizontal Cross‐Track Ion Drift Velocities in the High‐Latitude Ionosphere

AbstractHigh‐latitude ionospheric plasma convection plays a fundamental role in determining many processes in the terrestrial ionosphere. Electric Field Instruments on the European Space Agency's three polar‐orbiting Swarm satellites measure ionospheric ion drift velocities at about 500 km altitude using thermal ion imager energy/angle‐of‐arrival electrostatic analyzers. Recently, European Space Agency released horizontal cross‐track components of these drifts, calibrated at high latitudes. This paper concerns the validation of the Swarm horizontal cross‐track ion drift measurements. All available Swarm‐A and Swarm‐B 2 Hz data between November 2015 and July 2017 were used and the climatology of high‐latitude ion convection was constructed and examined. Results were compared to corresponding climatology obtained from the Weimer 2005 empirical convection electric field model under different interplanetary magnetic field and solar wind conditions in the northern and southern hemispheres, separately. The ion drift data sometimes exhibit large offsets at middle latitudes. However, following a recalibration of the drifts using a refinement of the offset removal, the Swarm cross‐track ion drift climatology agrees reasonably well statistically with the Weimer 2005 model, and properly responds to the changing geospace environment. The two results agree within about 200 m/s (root‐mean‐square deviation), however the correlations are higher for southward interplanetary magnetic field and in the northern hemisphere (rswarm‐A = 0.84, rswarm‐B = 0.77), for which the corresponding magnitudes of Swarm‐A and Swarm‐B drifts are ~14% and ~33% larger than the model estimates, respectively. The convection patterns seen in the revised Swarm horizontal cross‐track drift velocities are more structured than those obtained using the model, but overall no significant systematic errors are present.

The role of the convection electric field in filling the slot region between the inner and outer radiation belts

AbstractThe Van Allen Probes have reported frequent flux enhancements of 100s keV electrons in the slot region, with lower energy electrons exhibiting more dynamic behavior at lower L shells. Also, in situ electric field measurements from the Combined Release and Radiation Effects Satellite, Time History of Events and Macroscale Interactions during Substorms (THEMIS), and the Van Allen Probes have provided evidence for large‐scale electric fields at low L shells during active times. We study an event on 19 February 2014 where hundreds of keV electron fluxes were enhanced by orders of magnitude in the slot region and electric fields of 1–2 mV/m were observed below L = 3. Using a 2‐D guiding center particle tracer and a simple large‐scale convection electric field model, we demonstrate that the measured electric fields can account for energization of electrons up to at least 500 keV in the slot region through inward radial transport.

Transport of the plasma sheet electrons to the geostationary distances

AbstractThe transport and acceleration of low‐energy electrons (50–250 keV) from the plasma sheet to the geostationary orbit were investigated. Two moderate storm events, which occurred on 6–7 November 1997 and 12–14 June 2005, were modeled using the Inner Magnetosphere Particle Transport and Acceleration model (IMPTAM) with the boundary set at 10 RE in the plasma sheet. The output of the IMPTAM was compared to the observed electron fluxes in four energy ranges (50–225 keV) measured by the Synchronous Orbit Particle Analyzer instrument onboard the Los Alamos National Laboratory spacecraft. It was found that the large‐scale convection in combination with substorm‐associated impulsive fields is the drivers of the transport of plasma sheet electrons from 10 RE to geostationary orbit at 6.6 RE during storm times. The addition of radial diffusion had no significant influence on the modeled electron fluxes. At the same time, the modeled electron fluxes are one (two) order(s) smaller than the observed ones for 50–150 keV (150–225 keV) electrons, respectively, most likely due to inaccuracy of electron boundary conditions. The loss processes due to wave‐particle interactions were not considered. The choice of the large‐scale convection electric field model used in simulations did not have a significant influence on the modeled electron fluxes, since there is not much difference between the equipotential contours given by the Volland‐Stern and the Boyle et al. (1997) models at distances from 10 to 6.6 RE in the plasma sheet. Using the TS05 model for the background magnetic field instead of the T96 model resulted in larger deviations of the modeled electron fluxes from the observed ones due to specific features of the TS05 model. The increase in the modeled electron fluxes can be as large as two orders of magnitude when substorm‐associated electromagnetic fields were taken into account. The obtained model distribution of low‐energy electron fluxes can be used as an input to the radiation belt models. This seed population for radiation belts will affect the local acceleration up to relativistic energies.

Transport and loss of the inner plasma sheet electrons: THEMIS observations

[1] Using the electron data from the Time History of Events and Macroscale Interactions during Substorms (THEMIS) spacecraft measurements from 2007 to 2009, we derived global phase space density (PSD) distributions of plasma sheet electrons (2–100 eV/nT) to examine the transport process of the electrons to the inner magnetosphere and possible loss mechanisms of plasma sheet electrons during the convective transport. The inner boundaries of the electron plasma sheet were determined by the observed global distributions and compared with the Alfven boundaries that were calculated by the sum of the simple corotation and convection electric field models. This comparison confirms the previous results that the large-scale convection electric field controls the electron transport to the inner magnetosphere. The gradual decrease in PSD is observed from the dawn to the dayside sector, indicating the existence of some loss mechanisms in the morning sector. The loss time scales estimated from the PSD distributions were compared with the theoretical ones based on the quasi-linear diffusion theory using an empirical wave model of whistler mode chorus. We also estimated the required wave amplitudes that can explain the estimated loss time scales. It is shown that whistler mode chorus has a sufficient power to scatter the plasma sheet electrons, and the required wave amplitudes are roughly consistent with the CRRES statistical survey of the chorus wave amplitude. We suggest that the loss of plasma sheet electrons in the morning sector is mainly induced by pitch angle scattering by whistler mode chorus.

Influence of the convection electric field models on predicted plasmapause positions during magnetic storms

In the present work, we determine how three well documented models of the magnetospheric electric field, and two different mechanisms proposed for the formation of the plasmapause influence the radial distance, the shape and the evolution of the plasmapause during the geomagnetic storms of 28 October 2001 and of 17 April 2002. The convection electric field models considered are: McIlwain's E5D electric field model, Volland‐Stern's model, and Weimer's statistical model compiled from low‐Earth orbit satellite data. The mechanisms for the formation of the plasmapause to be tested are: (1) the MHD theory where the plasmapause should correspond to the last‐closed‐equipotential (LCE) or last‐closed‐streamline (LCS), if the E‐field distribution is stationary or time‐dependent respectively; (2) the interchange mechanism where the plasmapause corresponds to streamlines tangent to a Zero‐Parallel‐Force surface where the field‐aligned plasma distribution becomes convectively unstable during enhancements of the E‐field intensity in the nightside local time sector. The results of the different time dependent simulations are compared with concomitant EUV/IMAGE observations when available. The plasmatails or plumes observed after both selected geomagnetic storms are predicted in all simulations and for all E‐field models. However, their shapes are quite different depending on the E‐field models and the mechanisms that are used. Despite the partial success of the simulations to reproduce plumes during magnetic storms and substorms, there remains a long way to go before the detailed structures observed in the EUV observations during periods of geomagnetic activity can be accounted for very precisely by the existing E‐field models. Furthermore, it cannot be excluded that the mechanisms currently identified to explain the formation of “Carpenter's knee” during substorm events, will have to be revised or complemented in the cases of geomagnetic storms.

Imaging cold ions in the plasma sheet from the Equator‐S satellite

Energy‐dispersed H+ structures observed by Equator‐S in the sub‐keV range in the dawn sector of the ring current region were used to perform the remote sensing of cold ions in the near‐earth plasma sheet. A time history of the source distribution function in the nightside plasma sheet was reconstructed by using the phase space mapping method under a time‐dependent convection electric field model. We obtained the following major conclusions: (1) A cold H+ component (∼10 eV) exists in the near‐earth plasma sheet. (2) The cold component is readily distinguished from the main component of the plasma sheet (>∼a few keV). (3) The cold component is distributed over a relatively wide area in MLT. (4) Energy‐dispersed H+ structures in the inner magnetosphere results from temporal variation of the cold component. Our scheme will be applicable for investigating long‐term plasma processes acting on the cold component whose behavior is largely unknown.

Modeling geomagnetic storm dynamics: New results and challenges

Theoretical approaches to quantitatively model the dynamics of energetic ions and electrons in the coupled inner magnetosphere and the challenges they pose are briefly reviewed. Recent studies have shown the importance of high-resolution convection electric field models for reproducing ring current injection and morphology, and the necessity of development of models that calculate self-consistently the inner magnetospheric electric and magnetic fields. In situ observations have indicated that besides radial diffusion, local acceleration processes may contribute as well to the transport and energization of radiation belt particles, thus demonstrating the need of including self-consistent treatment of transport and wave instabilities in models. We present results from our physics-based model recently extended to relativistic energies, which solves the kinetic equation for H + , O + , and He + ions and electrons, and simulates the global distribution and variability of these populations during geomagnetic storms. The model is coupled with a time-dependent plasmasphere model and includes time-varying plasma inflow from the magnetotail, both convective and diffusive transport, and losses due to collisions, dayside outflow, and self-consistent wave-particle interactions. The model reproduces well ring current buildup during the rapid main phase of the 21 October 2001 large geomagnetic storm with Dst = - 187 nT , but underestimates the second Dst = - 165 nT minimum on 23 October. New results from this coupled ring current–radiation belt model demonstrate that strong electromagnetic ion cyclotron (EMIC) and whistler mode waves may be excited by the anisotropic ring current populations during storm time. Our simulations of ring current dynamics during a detached proton auroral arc event observed with the instruments on IMAGE satellite show that pitch angle scattering by the EMIC waves causes significant proton precipitation into the atmosphere in the postnoon sector, in good agreement with observations.

Evolution of the proton ring current energy distribution during 21–25 April 2001 storm

Three ring current models are used to follow the evolution of the proton ring current during the 2001‐04‐21–25 storm: The ring current model combined with tracing particles numerically in the drift approximation by Ganushkina et al. (2005), the empirical model of proton fluxes in the inner magnetosphere developed by Milillo et al. (2003), and the kinetic ring current‐atmosphere interaction model (RAM) by Liemohn et al. (2001). The paper focuses on the effects of the electric and magnetic field models and initial particle distributions on the final energy distribution. We examine a variety of large‐scale magnetic field and convection electric field models as well as substorm‐associated, smaller‐scale, and time‐varying electric fields. We find that (1) using more realistic magnetic field models leads to reduction of the ring current energy content by ∼30%; (2) details of the global convection field have little influence on the overall ring current evolution; (3) smaller‐scale impulsive electric field have profound effects on the ring current evolution, particularly with regard to the acceleration of the higher‐energy particles; and (4) in the ring current models, the choice of the initial and boundary conditions have significant effects on the modeled ring current intensity and energy spectrum.

Multiple discrete-energy ion features in the inner magnetosphere: 9 February 1998, event

Abstract. Multiple discrete-energy ion bands observed by the Polar satellite in the inner magnetosphere on 9 February 1998 were investigated by means of particle simulation with a realistic model of the convection electric field. The multiple bands appeared in the energy vs. L spectrum in the 1–100 keV range when Polar traveled in the heart of the ring current along the outbound and inbound paths. We performed particle tracing, and simulated the energy vs. L spectra of proton fluxes under the dipole magnetic field, the corotation electric field, and the realistic convection electric field model with its parameters depending on the solar wind data. Simulated spectra are shown to agree well with the observed ones. A better agreement is achieved when we rotate the convection electric potential eastward by 2h inMLT and we change the distribution function in time in the near-Earth magnetotail. It is concluded that the multiple bands are likely produced by two processes for this particular event, that is, changes in the convection electric field (for >3keV protons) and changes in the distribution function in the near-Earth magnetotail (for <3keV protons). Key words. Magnetospheric physics (energetic particles, trapped; electric field) – Space plasma physics (numerical simulation studies)

Magnetospheric convection electric field dynamics andstormtime particle energization: case study of the magneticstorm of 4 May 1998

Abstract. It is shown that narrow channels of high electric field are an effective mechanism for injecting plasma into the inner magnetosphere. Analytical expressions for the electric field cannot produce these channels of intense plasma flow, and thus, result in less entry and adiabatic energization of the plasma sheet into near-Earth space. For the ions, omission of these channels leads to an underprediction of the strength of the stormtime ring current and therefore, an underestimation of the geoeffectiveness of the storm event. For the electrons, omission of these channels leads to the inability to create a seed population of 10-100 keV electrons deep in the inner magnetosphere. These electrons can eventually be accelerated into MeV radiation belt particles. To examine this, the 1-7 May 1998 magnetic storm is studied with a plasma transport model by using three different convection electric field models: Volland-Stern, Weimer, and AMIE. It is found that the AMIE model can produce particle fluxes that are several orders of magnitude higher in the L = 2 – 4 range of the inner magnetosphere, even for a similar total cross-tail potential difference. Key words. Space plasma physics (charged particle motion and acceleration) – Magnetospheric physics (electric fields, storms and substorms)

Ring current asymmetry from global simulations using a high‐resolution electric field model

We study ring current evolution during the 10 January 1997 geomagnetic storm, comparing results from two inner magnetospheric convection electric field models: (1) the Kp‐dependent Volland‐Stern (V‐S) model and (2) the high spatial and temporal resolution assimilative mapping of ionospheric electrodynamics (AMIE) model, coupled with our global ring current model. We have added a penetration electric field (driven by partial ring current closure in the ionosphere) to the AMIE model which improves the agreement at low L shells with Polar/EFI measurements, and we mapped the modified AMIE convection electric potentials (MACEP) to the equatorial plane. Both V‐S and MACEP convection models predict a very asymmetric local time distribution of ring current energy density during the main and early recovery phase of the storm. However, the peak of the medium energy ions is located during the main phase near midnight when the MACEP model is used, while it is located near dusk using V‐S. In both models the energy density peak is located near dusk during the early recovery, and the ring current becomes symmetric during the late recovery phase. Ring current injection is larger, penetrating to lower L shells, and the Dst index is significantly better reproduced using MACEP rather than using V‐S model. We compare model results with Polar data and find reasonably good agreement with both models at larger L shells and near dawn. The enhanced storm time distributions at low L shells near dusk are better modeled with MACEP. Electromagnetic ion cyclotron (EMIC) waves are predominantly excited near Dst minimum, have larger wave gain, and cause stronger ion precipitation using the MACEP model. In this case the calculated ion precipitation patterns exhibit features consistent with storm time Polar/IPS observations and show enhancements within the plasmaspheric bulge and along the duskside plasmapause. In the dusk to midnight sector at L > 5, however, there seems to be a need to include the effect of an additional scattering process during highly active conditions.

Thermal plasmaspheric morphology: Effect of geomagnetic and solar activity

A multispecies kinetic model of the thermal plasma in the plasmasphere is used to predict the spatial dependence of the hydrogen ion and helium ion density and temperature for different levels of geomagnetic and solar activity. The particular convection electric field model chosen is intended for the time intervals between substorms. The plasma density and temperature in the equatorial plane are found to exhibit a local‐time variation that is sensitive to the details of the convection electric field. In particular, the parallel temperature increases with altitude and the perpendicular temperature decreases with altitude, except in the postmidnight sector, features that are only possible if kinetic effects are taken into account. In addition, the ratio of the helium ion density to the hydrogen ion density is found to agree with observations of the Dynamics Explorer 1 satellite. This behavior can be explained by the effects of convection on the thermal particles that are magnetically trapped on closed field lines. These results have implications for the interpretation and analysis of sunlight scattered by helium ions (He II) to be measured by future global imaging satellites.

Observations of downward moving O+ in the polar topside ionosphere

New investigations of the core ion motion within the high‐latitude topside ionosphere and near‐Earth magnetosphere, using data from the Dynamics Explorer retarding ion mass spectrometer (RIMS), reveal the existence of significant regions of downward moving O+. The occurrences of downgoing versus upgoing O+ are not clearly separable in terms of either solar zenith angle or Kp but are well distinguished by the direction of the z component of the interplanetary magnetic field (IMF). On average, downflow dominates when IMF Bz < 0, while upflow dominates for IMF Bz > 0. Combining cross‐field convection velocities derived from an empirical convection electric field model with the observed parallel velocities yields a two‐dimensional ion velocity field. This velocity field is consistent with a scenario which has O+ of cusp/cleft and auroral zone origin convecting into the polar cap and, because of the dominance of gravitational energy over the upward kinetic energy, falling back into the ionosphere. This provides additional confirmation of the results of studies of the cleft ion fountain. Estimates of the flux of O+ in the upflowing and downflowing regions for Λ ≥ 60° give a total upflow of ∼6 × 1025 ions s−1 for IMF Bz > 0 and total upflow and downflow of ∼4 × 1025 ions s−1 and 1 × 1025 ions s−1, respectively, for IMF Bz < 0. In all cases the magnitude of the dayside outflow is consistent with previous work on upwelling ions. While the magnitudes vary for high and low Kp the ratios of upward to downward flow are roughly the same at ∼1.7. The downflowing O+ shows a correlation with the magnitude of the outflow of light ions in the same region but the cause and effect of this relationship is not distinguishable.

Effect of the large-scale convection electric field structure on the formation of thin ionization layers at high latitudes

A three-dimensional simulation of the high-latitude ionosphere was applied to investigate the geographical distribution of E-region thin ionization layers which may be formed by the action of the convection electric field. The simulation model computes the ion densities (O +, O + 2, N +, N + 2, NO +, Fe +), and temperatures as a function of altitude, latitude, and longitude. The stationary state momentum and continuity equations are solved for each ion species, then the energy equation is solved for electrons, neutrals, and a generic ion having the mean ion mass and velocity. The various electric field patterns of the Heppner and Maynard [(1987) J. geophys. Res. 92, 4467–4489] convection electric field model were applied and the ionization density pattern was examined after a time sufficient for the formation of thin layers (≈2000 s). It was found that large areas of thin ionization layers were formed for each of the electric field patterns examined. Southward IMF B z conditions resulted in thin layers forming in the pre-midnight sector in the latitude range north of about 70° to about 80°, and after midnight between 60 and 70°. For northward B z conditions, the layers were mainly in the pre-midnight sector and covered a latitude range from about 60 to 80°.

Simulations of the behaviour of the polar thermosphere and ionosphere for northward IMF

The dynamics and structure of the polar thermosphere and ionosphere within the polar regions are strongly influenced by the magnetospheric electric field. The convection of ionospheric plasma imposed by this electric field generates a large-scale thermospheric circulation which tends to follow the pattern of the ionospheric circulation itself. The magnetospheric electric field pattern is strongly influenced by the magnitude and direction of the interplanetary magnetic field (IMF), and by the dynamic pressure of the solar wind. Previous numerical simulations of the thermospheric response to magnetospheric activity have used available models of auroral precipitation and magnetospheric electric fields appropriate for a southward-directed IMF. In this study, the UCL/Sheffield coupled thermosphere/ionosphere model has been used, including convection electric field models for a northward IMF configuration. During periods of persistent strong northward IMF B z , regions of sunward thermospheric winds (up to 200 m s −1) may occur deep within the polar cap, reversing the generally anti-sunward polar cap winds driven by low-latitude solar EUV heating and enhanced by geomagnetic forcing under all conditions of southward IMF B z . The development of sunward polar cap winds requires persistent northward IMF and enhanced solar wind dynamic pressure for at least 2–4 h, and the magnitude of the northward IMF component should exceed approximately 5 nT. Sunward winds will occur preferentially on the dawn (dusk) side of the polar cap for IMF B y negative (positive) in the northern hemisphere (reverse in the southern hemisphere). The magnitude of sunward polar cap winds will be significantly modulated by UT and season, reflecting E-and F-region plasma densities. For example, in northern mid-winter, sunward polar cap winds will tend to be a factor of two stronger around 1800 UT, when the geomagnetic polar cusp is sunlit, then at 0600 UT, when the entire polar cap is in darkness.

Decay of equatorial ring current ions and associated aeronomical consequences

The decay of the major ion species which constitute the ring current is studied by solving the time evolution of their distribution functions during the recovery phase of a moderate geomagnetic storm. In this work, only equatorially mirroring particles are considered. Particles are assumed to move subject to E×B and gradient drifts. They also experience losses along their drift paths. Two loss mechanisms are considered: charge exchange with neutral hydrogen atoms and Coulomb collisions with thermal plasma in the plasmasphere. Thermal plasma densities are calculated with a plasmaspheric model employing a time‐dependent convection electric field model. The drift‐loss model successfully reproduces a number of important and observable features in the distribution function. Charge exchange is found to be the major loss mechanism for the ring current ions; however the important effects of Coulomb collisions on both the ring current and thermal populations are also presented. The model predicts the formation of a low‐energy (< 500 eV) ion population as a result of energy degradation caused by Coulomb collisions of the ring current ions with the plasmaspheric electrons; this population may be one source of the low‐energy ions observed during active and quiet periods in the inner magnetosphere. The energy transferred to plasmaspheric electrons through Coulomb collisions with ring current ions is believed to be the energy source for the electron temperature enhancement and the associated 6300 Å (stable auroral red [SAR] arc) emission in the subauroral region. The calculated energy‐deposition rate is sufficient to produce a subauroral electron temperature enhancement and SAR arc emissions that are consistent with observations of these quantities during moderate magnetic activity levels.

Quantitative patterns of large‐scale field‐aligned currents in the auroral ionosphere

Quantitative patterns of the distribution of field‐aligned current (FAC) density have been derived from gradients of the average patterns of the Hall and Pedersen currents at high latitudes under the assumption that the total current is divergence‐free. The horizontal currents were calculated from empirical convection electric field models, derived from Millstone Hill radar observations, and the ionospheric Hall and Pedersen conductances, based on satellite observations of the precipitating particle energy flux and spectrum and including an average (equinox) solar contribution. These independent empirical models, and the resultant patterns of the field‐aligned currents, are keyed to an auroral precipitation index which quantifies the intensity and spatial extent of high‐latitude particle precipitation and which is determined from a single satellite crossing of the auroral precipitation pattern. The patterns detail the spatial distribution of the currents as a function of increasing disturbance level. The magnitudes of the total single‐hemisphere currents into or out of the ionosphere are closely balanced at each activity level and increase exponentially between 0.1 and 6 MA with increasing values of the precipitation index. The interplanetary magnetic field (IMF) sector dependence of the FAC patterns is investigated for disturbed conditions. A large portion of the FAC pattern is closed by local Pedersen currents (current into the ionosphere is balanced by an equal current out of the ionosphere at that local time). This locally balanced portion of the FAC system is enhanced in the prenoon (postnoon) sector for IMF By > +1 nT (By < −1 nT). In addition, there are net currents into the ionosphere postnoon and out of the ionosphere in the premidnight sector. Whereas the magnitude of these nighttime net FACs increases with increasing negative IMF Bz, the magnitude and distribution of the net currents appear to be independent of the IMF By orientation.

On the transport of ions released in the magnetotail by the AMPTE-IRM satellite

The Ba and Li ions that were released in the magnetotail in the Spring, 1985, by the AMPTE-IRM satellite were not observed subsequently in the inner magnetosphere with the AMPTE-CCE satellite. These results were studied by using a Monte Carlo code to compute the transport of the ions. For each release several hundred ion guiding-center trajectories were computed under simulated magnetospheric conditions, using the Tsyganenko-Usmanov magnetic field model and the Millstone-Hill convection electric field model. The corotation and convection electric fields were mapped to altitudes above the ionosphere assuming the magnetic field lines to be equipotentials. The initial conditions of the ions, at the times at which the ions were picked up by the electric field, were estimated by taking into consideration the release conditions and the early-time collective effects. The results indicate that the Ba + ions were not observed because the CCE satellite was not along the drift paths of the ions, and the Li + ions were not observed because their fluxes at the satellite were too low.

Electron density near the plasmapause, modified experimental parameters for the volland convection electric field and field-aligned current distribution deduced from the global field model

This paper presents the results of a statistical analysis made on the electron density data obtained over one year by the Relaxation Sounder (RS) onboard the GEOS-2 ESA satellite. The annually overaged daily profile is given. A seasonal variation of the plasma density in the equatorial plane is clearly apparent, i.e. the electron density is larger in summer than in winter. By combining the equatorial electron density data and data obtained in the auroral ionospheric region, we can deduce the parameters of the Volland convection electric field model and calculate the associated field-aligned current distributions, which roughly agree with the observed ones.