The concept of the auroral oval was proposed independently by Feldstein and by Khorosheva in the early 1960's, and it has since been widely used as a reference frame for the organization of high‐latitude optical, particle, and ionospheric data. More recently, different structural regions associated with the oval have been distinguished, and these have been identified with different magnetospheric regions by different workers. The net result is an inconsistent set of nomenclature and relationships. The literature of this development is reviewed in detail, and an interpretation and terminology that is consistent, in the opinion of the authors at least, are proposed. It is hoped that this proposal will serve as a useful basis for further discussion on the ordering of auroral phenomena in relation to the magnetosphere.

Abstract. We analyse measurements of ion spectral gaps (ISGs) observed by the ION particle spectrometer on board the Interball-2 satellite. The ISG represents a sharp decrease in H + flux at a particular narrow energy range. ISGs are practically always observed in the inner magnetosphere in a wide MLT range during quiet times. Clear examples of ISG in the morning, dayside, evening and nightside sectors of the magnetosphere are selected for detailed analysis and modeling. To obtain a model ISG, the trajectories of ions drifting in the equatorial plane from their nightside source to the observation point were computed for the energy range 0.1-15 keV. Three global convection models (McIlwain, 1972(McIlwain, , 1986Volland, 1973;Stern, 1975) were tested to reproduce the observed ISGs in all MLT sectors. Qualitative agreement is obtained for all three models, but the better agreement for quiet times is reached with the McIlwain (1972) convection model. It is shown that the ISGs observed by the ION spectrometer throughout the inner magnetosphere are the result of superposition of the two effects, already described in the literature (e.g. McIlwain, 1972;Shirai et al., 1997), but acting under different conditions. Also, the role of particle source location on the model gaps is investigated. It may be concluded that despite the evidence of large amplitude and directional local fluctuations of electric fields in the inner magnetosphere (Quinn et al., 1999), the existence of a stationary average convection pattern is confirmed by this modeling. This fact directly follows from observations of ISGs and from a good agreement of observations with modeled gaps calculated in the frames of adiabatic theory for a stationary (average) convection pattern.

Abstract. Recent analysis of the ground-based observations of the Polarization Jet (PJ) effects in the subauroral ionosphere has shown that PJ can rapidly develop in the nearmidnight sector near the Harang Discontinuity (HD). Based on these observations, a simple, semi-quantitative theory of the PJ formation and its main characteristics is constructed. According to the model, PJ starts to develop, as proposed by Southwood and Wolf, 1978, due to the penetration of the injected energetic ions to the deeper L-shells in the presence of the westward component of the electric field. The injection near the tip of the HD is assumed here. The initial development stage of the PJ band, considered only qualitatively, is supposed to lead to its inclination inward toward evening with respect to the lines B = const. Within the model proposed, the PJ band, once formed, will be sustained by the continuous charging at its equatorial side, at first, mainly by the newly injected ring current ions, and later by the plasma sheet ions convected inward through the HD. In addition, an important charging of the PJ band occurs at its polar side by energetic electrons drifting eastward. These electrons were either previously on the trapped orbits or convected inward from the plasma sheet, and encounter the PJ polar border. The model semi-quantitatively describes the main features of the PJ events: the typical cross-PJ voltage drop (∼ 10 kV), the resulting double-sheet current loop feeding the PJ, the recently observed short PJ formation time near midnight (∼ 10 min or less) accompanied by a fast westward HD displacement, the nearly steady-state PJ location in the evening to midnight MLT sector and width in the ionospheric frame, the bell-shape of the electric field latitude profile, and the long PJ lifetime (up to several hours) -all are in rough accord with observations. Further developments of the model now in progress are briefly described.

Polarization Jet (PJ), also known as Sub‐Auroral Ion Drift (SAID), events are supersonic westward plasma drifts on the equatorward edge of the diffuse aurora in the evening and nighttime sector. Their optical F‐region signatures are weak 630.0 nm red arcs colocated with regions of fast convection. These weak arcs resemble Stable Auroral Red (SAR) arcs observed during the recovery phase of magnetic storms, but have lower intensities, shorter lifetimes, and occur without a significant heat flux from the magnetosphere. Previous model studies underestimated the brightness of weak SAR arcs. We present calculations showing that ion‐neutral collisional heating and ion composition changes during PJ events may be an additional source of 630.0 nm emission, and propose experimental tests that could verify our modeling results.

Westward cross‐tail current at the earthward edge of the plasma sheet is enhanced due to strongly stochastic (rLi ∼ Rc) ion motions. A narrow elongated magnetic field depression arises which leads to further stochastication of the ions convecting through it, and to a local increase of magnetostatic plasma pressure, enhanced lateral transport and removal of higher energy ions. This plasma structure can be stationary in the magnetospheric frame. It is the “root” of sheet‐like auroral currents of stable auroral homogeneous arcs/bands (inverted‐V's) located at the equatorial edge of the steady premidnight auroral oval. The magnetic field minimum can be the location of a sub‐storm onset when it deepens below the stability threshold for reconnection/tearing.