Yu. I. Gal'Perin

On the acoustoelectric current in a one-dimensional channel

We report the first observation of the direct current induced by a surface acoustic wave through a quantum point contact defined in a GaAs - AlGaAs two-dimensional electron gas by means of a split gate. We have observed giant oscillations in the acoustoelectric current as a function of gate voltage, with minima corresponding to the plateaux in quantum point contact conductivity. A theoretical consideration is presented which explains the observed peaks in terms of the matching of sound velocity with electron velocity in the upper one-dimensional subband of the quantum point contact.

Predicting plasmaspheric radial density profiles

A principle question concerning storm time convection is, What physical process or measurable parameter controls the location of the equatorward edge of the large-scale convection zone expansion during magnetic storms and hence the plasmapause location? Experimental data on convection and particle precipitation consistently show that in the evening to midnight local time sector, the inner boundary of the high-latitude westward ion convection band colocates with the equatorward boundary of soft electron precipitation (SEB). Low-energy electron precipitation is usually absent, or very weak, above the lower-latitude band of the disturbed-time double-peaked convection pattern. It follows that large-scale convection streamlines carrying plasma sheet particles do not enter the polarization jet band which lies on the opposite (inner) side of the Alfven layer, which limits the inward expansion of hot plasma and convection by polarizing the edge of the inner magnetosphere plasma population. We conclude that the SEB (measured and/or modeled) can be used in plasmasphere density models as a substitute for the convection boundary. A time-dependent convection-driven plasmaspheric density model (CDPDM) is introduced to describe plasmaspheric thermal density profiles. The CDPDM is based on the convection drift and refilling rate prehistory calculated for a particular plasma flux tube, and its most important ingredient is a realistic convection model for disturbed times. Sharp density gradients (plasmapauses) on the radial profiles are indicators of preceding convection boundary locations outside of which the thermal plasma content was lost. We compare the predictions of the model with storm time ionospheric observations with the Millstone Hill radar and conclude that the CDPDM can be used to predict the locations of plasma density radial gradients, including the plasmapause.

An alternative interpretation of auroral precipitation and luminosity observations from the DE, DMSP, AUREOL, and Viking satellites in terms of their mapping to the nightside magnetosphere

Abstract We present an interpretation, which differs from that commonly accepted, of several published case studies of the patterns of auroral electron precipitation into the high-latitude upper atmosphere in the near-midnight sector based on their mapping to the nightside magnetosphere. In our scheme bright discrete auroral structures of the oval and respective precipitation are considered to be on the field lines of the Central, or Main, Plasma Sheet at distances from 5–10 to 30–50 RE, depending on activity. This auroral electron precipitation pattern was discussed in detail by Feldstein and Galperin [(1985) Rev. Geophys.23, 217] and Galperin and Feldstein [(1991) Auroral Physics, p. 207. Cambridge University Press. It is applied and shown to be consistent with the results of case studies based on selected transpolar passes of the DE, DMSP, AUREOL-3 and Viking satellites. A diagram summarising the polar precipitation regions and their mapping from the magnetospheric plasma domains is presented. It can be considered as a modification of the Lyons and Nishida (1988) scheme which characterizes the relationship between the gross magnetospheric structure and regions of nightside auroral precipitation. The modification takes into account non-adiabatic ion motions in the tail neutral sheet, so that the ion beams characteristic of the Boundary Plasma Sheet (BPS) originate on closed field lines of the distant Central Plasma Sheet (say, at distances more than ~30 RE).

Positive ion distributions in the morning auroral zone: Local acceleration and drift effects

Abstract We report on the typical structure of the large scale ion precipitation in the morning sector of the auroral zone and associated low frequency electromagnetic waves. Data obtained during near radial passes of the AUREOL-3 satellite point to a distinction between two main precipitation regions: 1) In the poleward part of the auroral zone the latitudinal variation of the average energy (or temperature) of the precipitated ions (mainly H+) indicate that they are adiabatically accelerated in the outer magnetosphere. This “high energy” (⋍ 3 to > 20 keV) precipitation is usually associated with a low energy (E 3 hours) we suggest that the precipitation of ionospheric ions inside the diffuse aurora results from convection and corotation of the ions accelerated to suprathermal energies at higher latitudes.

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

Abstract 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.

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.

Low-frequency shot noise in double-barrier resonant-tunnelling structures in a strong magnetic field

Low-frequency shot noise and dc current profiles for a double-barrier resonant-tunnelling structure (DBRTS) under a strong magnetic field applied perpendicular to the interfaces have been studied. Structures with a 3D and 2D emitter have both been considered. The calculations, carried out with the Keldysh Greens function technique, show strong dependencies of both the current and noise profiles on the bias voltage and magnetic field. The noise spectrum appears sensitive to charge accumulation due to barrier capacitances, and both noise and dc current are extremely sensitive to the Landau level broadening in the emitter electrode and can be used as a powerful tool to investigate the latter. As an example, two specific shapes of the level broadening have been considered - a semi-elliptic profile resulting from the self-consistent Born approximation, and a Gaussian one resulting from the lowest-order cumulant expansion.

FORMATION OF POLARIZATION JET DURING INJECTION OF IONS INTO THE INNER MAGNETOSPHERE

Long-lasting ground based measurements of a polarization jet (PJ) by the latitudinal chain of ionospheric stations in Yakutia (3 500 nT.

Magnetospheric tail structure: concepts, problems and storm-time development of the auroral oval

Abstract This paper reviews current knowledge on links between the Earths magnetic tail and the auroral oval, and identifies some problems remaining. It considers electrons as tracers of the geomagnetic field, boundaries between different regions, plasma flows, and pressure balance conditions. The auroral arc is considered as a standing discontinuity in the flow of central plasma sheet (CPS) plasma field-aligned current systems are also proposed. The plasma instability responsible for the breakup phase of an auroral substorm is also discussed.

Polar Wind Observations on the Nightside of the Polar Cap at Altitudes of 2–3 RE: Results of the INTERBALL-2 Satellite

The results of measuring the fluxes of ionospheric ions in the nightside polar cap at an altitude of about 20 000 km are presented. The data are obtained with the HYPERBOLOID instrument onboard the INTERBALL-2 satellite. The passages without intense precipitation of magnetospheric ions and electrons have been selected using the ION instrument data, so that the observation of ionospheric ion fluxes caused by heating in the auroral regions can be excluded. In addition, an attempt has been made to exclude observations of the “cleft ion fountain” from the analysis. The measurements in the summer and winter seasons (when the ionosphere was totally sunlit and completely shadowed, respectively) are considered separately. By analyzing the distribution functions of the fluxes measured, we have isolated six different types of ionospheric plasma flows in the polar cap. A strong distinction has been revealed between summer and winter flows. In winter, only weak flows of H+ ions were detected. In the summer period, we detected both H+ and O+ ions. The flux values of the ionosphere ions are found to be strongly dependent on the intensity of the polar rain. The measurements are compared to the existing models of the polar wind. The best models (for the description of our measurements) are indicated. After the choice of measurement periods, the resulting region coincides with the ion depletion zone (IDZ). Based on the earlier measurements by the AKEBONO satellite, nothing could be said about the fluxes of thermal ions in this zone, because of the insufficient sensitivity of the instrument aboard this satellite.