Nonlinear Localized Electrostatic Structures and Their Experimental Diagnostics in the Magnetosphere Plasma

The theoretical models of the formation of the three-dimensional quasi-stationary structures of variations of density and electrostatic potential in a multicomponent magnetosphere plasma are considered. On the basis of the perturbation method, we have studied the domains of the parametric space, where the occurrence of nonlinear quasi-stationary ion-acoustic and electron-acoustic structures are possible. For these structures, the velocities of motion along the direction of the magnetic field are estimated, together with the longitudinal and transverse scales with respect to the direction of the Earth's magnetic field. The calculated dependences of the scales l and l _|| of the structures on the plasma parameters in the three-component plasma allow one to compare the results of the considered theoretical models with new experimental data of measuring the form of soliton structures onboard the FAST, POLAR, and GEOTAIL satellites.     

Statistical study of inverted-V events: A comparison between experiment and theory

We present a detailed study of the distribution and of the internal structure of the inverted-V electron precipitation commonly detected in the 500 – 2000 km altitude range aboard the AUREOL-3 satellite. These structured precipitations are statistically observed inside the auroral oval with a maximum occurence in the nightside sector. They correspond to primary electron fluxes peaked at energies generally below 10 keV. It is shown that, as predicted by kinetic theories, most inverted-V structures present a clear relationship between the field-aligned current density carried by the 1 – 20 keV primary electrons and the potential drop inferred from particle distribution functions. Furthermore the study demonstrates the existence of strong electron heating, related to the energy gain, when the current density exceeds some threshold of about 1 – 5 μA(m)^?2.     

A New Population of the Cusp Suprathermal Protons Formed at Mid-Altitudes: INTERBALL-2 Measurements

A new population of dispersed suprathermal ions descending into the ionosphere is discovered in the cusp region from theINTERBALL-2 measurements at altitudes of 2–3R _E. The proton energies of the population are below the low energy cut-off of the main dispersed proton population of the magnetosheath origin, and its intensity and density are also much lower. For IMF B _z 2 nT the region of the population observations is located partly coincident with (or sometimes poleward from) the main proton population of the cusp proper. The pitch-angle velocity dispersion in the population during a 2-min satellite rotation manifests itself as a typical pitch-angle V together with a velocity dispersion due to poleward convection. The satellite passes chosen for the detailed analysis and modeling lay approximately along the cusp/cleft band from afternoon till prenoon MLT sectors, thus emphasizing the pitch-angle dispersion role with respect to the dispersion due to convection. This allows one to observe the suprathermal proton population during several tens of minutes over the MLT range of 3 h around noon, i.e., similarly to the MLT extension of the cusp proper. A remarkable space/time stability of this new population is due to its low velocity (tens of km/s) and/or velocity diffusion in the flux tubes of the cusp proper. We have performed both backward tracing of proton trajectories in the Tsyganenko-96 model, and kinetic modeling of the kinematic variations of the distribution function for protons along their way from the bi-Maxwellian source in the form of a heating wall till the satellite. The parameters of the model were adjusted to the observed energy–time spectrograms. They consistently indicate the origin of the descending suprathermal proton population at intermediate altitudes of 5R _E, i.e., within cusp flux tubes but well below the magnetopause. Some published measurements from the POLAR satellite in the cusp region at altitudes of 4–5R _E seem to be consistent with the supposition of crossing the source region of this population, variable in space and time (though these measurements were interpreted in a different manner).     

Evidence for ion energy dispersion in the polar cusp related to a northward-directed IMF

Data from the particle experiment aboard the AUREOL-3 polar satellite show that about 30% of the summer cusp crossings are characterised by a clear latitudinal energy dispersion of the solar wind ions. This energy-latitude correlation is observed at very high latitudes, 80° – 85°, near the polar boundary of the cusp, as an increase of the ion average energy with latitude. These structures have a typical latitude extent of 1° – 2° at ionospheric heights and correspond to a northward-directed IMF. These observations are consistent with a sunward convection of the foot of the magnetic flux tubes recently merged with a northward directed interplanetary magnetic field.     

Particle and optical measurements aboard the Aureol 3 spacecraft (ARCAD 3 project): A — The particle experiments B — Optical measurements

The CESR Toulouse - IKI Moscow particle instrument package aboard the AUREOL-3 satellite consists of a complete set of charged particle spectrometers which measure electron and ion fluxes from 15 eV to 25 keV in 128 steps and in 11 directions. In addition, 4 channel spectrometers (2 electron and 2 ion channels in parallel) allow high time resolution measurements (up to 10 msec) with onboard calculation of auto and cross correlation functions. For higher energies (40 – 280 keV), solid-state spectrometers are used to measure electron and proton fluxes in 4 channels in parallel. In addition, two Geiger counters are used for the determination of the trapping boundaries. Two mass-energy ion spectrometers (1 to 32 A.M.U., 0.02 – 15 keV) are placed with viewing angles which allow a distinction between nearly isotropic auroral proton precipitation and conical beams accelerated in the auroral ionosphere. Auroral and airglow photometry is performed aboard the AUREOL-3 satellite by a set of 3 parallel directed photometers with tiltable interference filters for 6300 Å, 4278 Å and Doppler shifte H_β emissions. Various modes of energy, angular and mass scanning, correlation function calculation and various Soviet and French telemetry regimes provide the possibility of choosing the sequences of measurements according to particular experimental programs along the orbit. Finally, examples of data from inflight measurements using the above instruments are presented and briefly discussed, showing several interesting features.     

Field and wave measurements aboard the Aureol-3 spacecraft

In the Soviet-French Arcad-3 project, 3 experiments TBF-ONCH, TRAC and ISOPROBE are carried out on board the Aureol-3 satellite to measure the AC and DC electric and magnetic fields and waves. Several modes of telemetry, real time and memory regimes are available for data transmission. TBF-ONCH is devoted to the measurement of 3 components of the DC electric field, 2 electric and 3 magnetic components of the waves. In one mode of the real time telemetry these 5 components are transmitted simultaneously in the frequency range 10 Hz-1.5 kHz in order to be able to determine the wave normal directions of natural emissions and to localize their sources. In the second mode, morphological studies of saucers, chorus, hiss and triggered emissions can be undertaken using the wide band transmission (70 Hz-16 kHz) of any one of these 5 components with the possibility of periodically changing the transmitted component every 4 seconds or keeping the same one during all the pass. TRAC makes use of the on board 3 axis flux gate magnetometer to perform a fine measurement of the magnetic effects of the currents flowing in the vicinity of the spacecraft either in the ionosphere or along the magnetic field lines, with a resolution of ～ 12 nT and in the frequency range from DC to ～ 20 Hz. One component of the HF electric field (0.1–10 Mhz) is measured by ISOPROBE (see companion paper). Examples of inflight measurements from the above instruments and their presentation on microfiches are shown. Some new phenomena are emphasized and briefly discussed.     

Formation of a Polarization Jet during the Expansion Phase of a Substorm: Results of Ground-Based Measurements

The ground-based polarization jet measurements at the Yakutsk ionosphere station (L= 3.0) for the years 1989–1991 (110 events) are compared with variations of the AE-index and with parameters of the local magnetic activity. It is shown that polarization jet development in the near midnight sector can occur during a period of no longer than 10 min on the expansion phase of a substorm. The formation of the polarization jet is accompanied by a specific magnetic field variation corresponding in shape to a fast passage of the Harang Discontinuity above the station. Statistical data are given on ground level observations of the polarization jet, which are close to those measured from satellites. The mean delay (averaged over the full data bank) between the onset of a substorm with AE 500 nT and the moment of the polarization jet appearance at L= 3.0 is equal to 0.5 h near midnight and to 1.0 – 1.5 h in the evening sector. Estimations show that the duration of the polarization jet formation when energetic ions are injected into the Harang Discontinuity region above the ground station can last for about 10 min, and during this time the Harang Discontinuity can be shifted to the west. This is in qualitative agreement with the described observations.     

Electromagnetic Pulse in the Magnetosphere Generated by Impulsive Current near the Lower Boundary of the Ionosphere

A solution to the problem of current spreading is constructed in the case of relaxation of electric charges, which have arisen in the mesosphere for one reason or other. These currents penetrate into the conductive region with anisotropic conductivity of the D- and E-layers of the ionosphere, being transformed to a MHD-wave that propagates into the magnetosphere. Based on this solution, the form and spectrum of the generated MHD signal are calculated for Alfvenic and magnetosonic modes coming out to the ionosphere and magnetosphere. Electric charges and currents can arise, for example, in the space between a thunderstorm cloud and the ionosphere, or between the shock wave from a ground explosion and the ionosphere. Some signal parameters accepted in the model are close to those expected for high-altitude electric discharges of the Red Sprite type. The conditions are determined under which the Alfven impulse with an amplitude of up to 100 nT propagates in the magnetosphere above high-altitude discharge of this type. Such an impulse was recorded by the AUREOL-3 satellite after the ground explosion MASSA-1. Recently, this impulse was hypothesized to originate as a result of a high-altitude electric discharge. The hypothesis on a similar MHD pulse allows one to explain in a semiquantitative way the short burst of electron field-aligned acceleration observed by the DE-2 satellite over the Debbie hurricane. The high-altitude atmospheric discharge of this type can be a powerful, though short-time and local, source of electrons with kiloelectronvolt energies at low and middle latitudes. One could expect that such an effect causes a modified character of the so-called Trimpi-effect (a short-term disturbance of propagation of VLF waves in the ionosphere), and thus, it can be observable.