The STARE radars and the Scandinavian networks of magnetometers, all‐sky cameras, and riometers recorded during the night of October 21/22, 1979, the occurrence of a fairly regular sequence of auroral omega bands and associated magnetic and electric field variations. The combined two‐dimensional data are used to derive a realistic model for the three‐dimensional current flow associated with the auroral forms. In the model calculations the observed structure in the particle precipitation is accounted for by an inhomogeneous ionospheric conductivity distribution. The main resulting feature of the model current system is a sequence of east–west orientated pairs of upward and downward directed field‐aligned currents, associated with the bright and dark areas of the visual aurora, respectively. The major source of magnetic disturbances on the ground is a “meandering” ionospheric Hall current, composed of a westward background electrojet and circular Hall current vortices around the locations of the localized field‐aligned currents. The total magnetic disturbance observed on the ground during different events appears, however, to be strongly dependent on the Hall to Pedersen conductivity ratio and the degree of inhomogeneity in the conductivity distribution. The three‐dimensional current system associated with the auroral omega bands drifts eastward with a velocity comparable to an E×B drift within the general southward directed electric background field. However, complete agreement was not found at all times.

Abstract. The shape of the electron energy distribution has long been a central question in the field of highfrequency radio-induced optical emission experiments. This report presents estimates of the electron energy distribution function, f e (E), from 0 to 60 eV, based on optical multiwavelength (6300, 5577, 8446, 4278Å) data and 930-MHz incoherent scatter radar measurements of ion temperature, electron temperature and electron concentration. According to our estimate, the electron energy distribution has a depression at around 2 eV, probably caused by electron excitation of vibrational states in N 2 , and a high energy tail that is clearly supra-thermal. The temporal evolution of the emissions indicates that the electron temperature still plays an important role in providing electrons with energies close to 2 eV. At the higher energies the electron energy distribution has a nonthermal tail.

Enhancements of one, or both, of the ion‐acoustic peaks of incoherent scatter spectra in the auroral ionosphere have been observed with the EISCAT UHF and VHF radars. All occurrences for which optical data are available show these events to coincide with active, unusually intense, red auroral forms in the vicinity of the radar beam at high altitudes. Both the optical and the radar signatures are expected to be caused by large fluxes of low energy electrons. Analyses of the measured spectra, in which the electron drift speed is estimated, imply field‐aligned current densities up to several mA m−2. The vertically‐directed VHF observations from ∼1000 km altitude reveal that the spectral enhancements, which are transient features in field‐aligned measurements, can exist for up to several minutes.

Abstract. We report observations of a sequence of quiettime Earthward bursty bulk flows (BBFs) measured by the Cluster spacecraft in the near-tail plasma sheet (XGSM ∼ −12 to −14 R E ) in the evening sector, and by simultaneous highresolution measurements in the northern conjugate ionosphere by the EISCAT radars, a MIRACLE all-sky camera and magnetometers, as well as a meridian-scanning photometer (MSP) in the Scandinavian sector on 17 October 2005.The BBFs at Cluster show signatures that are consistent with the plasma "bubble" model Wolf, 1993, 1999), e.g. deflection and compression of the ambient plasma in front of the Earthward moving bubble, magnetic signatures of a flow shear region, and the proper flows inside the bubble. In addition, clear signatures of tailward return flows around the edges of the bubble can be identified. The duskside return flows are associated with significant decrease in plasma density, giving support to the recent suggestion by Walsh et al. (2009) of formation of a depleted wake. However, the same feature is not seen for the dawnside return flows, but rather an increase in density.In the ionosphere, EISCAT and optical measurements show that each of the studied BBFs is associated with an auroral streamer that starts from the vicinity of the polar cap boundary, intrudes equatorward, brakes at 68-70 • aacgm MLAT and drifts westward along the proton oval. Within the streamer itself and poleward of it, the ionospheric plasma flow has an equatorward component, which is the ionospheric manifestation of the Earthward BBF channel. A sharp velocity shear appears at the equatorward edge of a streamer. We suggest that each BBF creates a local velocity shear in the ionosphere, in which the plasma flow poleward of and inside the streamer is in the direction of the Correspondence to: T. Pitkänen (timo.pitkanen@oulu.fi) streamer and southeastward. A northwestward return flow is located on the equatorward side. The return flow is associated with decreased plasma densities both in the ionosphere and in the magnetosphere as measured by EISCAT and Cluster, respectively. In summary, we present the first simultaneous high-resolution observations of BBF return flows both in the plasma sheet and in the ionosphere, and those are in accordance with the bubble model. The results apply for the duskside return flows, but the manifestation of dawnside return flows in the ionosphere requires further studies.Finally, EISCAT measurements indicate increased nightside reconnection rate during the ∼35-min period of BBFs. We suggest that the observed temporal event of IMF rotation to a more southward direction produces enhanced open flux transport to the nightside magnetotail, and consequently, the nightside reconnection rate is increased.

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