Abstract. Using the auroral boundary index derived from DMSP electron precipitation data and the Dst index, changes in the size of the auroral belt during magnetic storms are studied. It is found that the equatorward boundary of the belt at midnight expands equatorward, reaching its lowest latitude about one hour before Dst peaks. This time lag depends very little on storm intensity. It is also shown that during magnetic storms, the energy of the ring current quanti®ed with Dst increases in proportion to v À3 e , where v e is the vvalue corresponding to the equatorward boundary of the auroral belt designated by the auroral boundary index. This means that the ring current energy is proportional to the ion energy obtained from the earthward shift of the plasma sheet under the conservation of the ®rst adiabatic invariant. The ring current energy is also proportional to i mg , the total magnetic ®eld energy contained in the spherical shell bounded by v e and v eq , where v eq corresponds to the quiet-time location of the auroral precipitation boundary. The ratio of the ring current energy i to the dipole energy i mg is typically 10%. The ring current leads to magnetosphere in¯ation as a result of an increase in the equivalent dipole moment.

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We demonstrate that the Super Dual Auroral Radar Network (SuperDARN) radar at Syowa station, Antarctica, can be used to detect high frequency radio wave attenuation in the D region ionosphere during energetic electron precipitation (EEP) events. EEP‐related attenuation is identified in the radar data as a sudden reduction in the backscatter power and background noise parameters. We focus initially on EEP associated with pulsating aurora and use images from a colocated all‐sky camera as a validation data set for the radar‐based EEP event detection method. Our results show that high‐frequency attenuation that commences during periods of optical pulsating aurora typically continues for 2–4 hr after the camera stops imaging at dawn. We then use the radar data to determine EEP occurrence rates as a function of magnetic local time (MLT) using a database of 555 events detected in 2011. EEP occurrence rates are highest in the early morning sector and lowest at around 15:00–18:00 MLT. The postmidnight and morning sector occurrence rates exhibit significant seasonal variations, reaching approximately 50% in the winter and 15% in the summer, whereas no seasonal variations were observed in other MLT sectors. The mean event lifetime determined from the radar data was 2.25 hr, and 10% of events had lifetimes exceeding 5 hr.

[1] We present, for the first time, a quasiperiodic modulation of ionospheric parameters, associated with the occurrence of pulsating auroras, such as electron density, conductance, and electric field. In March 2008, simultaneous campaign-based measurements of pulsating auroras were conducted over Tromsø (69.60°N, 19.20°E), Norway, using an all-sky TV camera (ATV) and the European Incoherent Scatter (EISCAT) UHF system. During an interval within this campaign period, pulsating auroras, with periods of 8-17 s, were observed by the ATV in the morning local time sector (∼0500 MLT). In this interval, quasiperiodic oscillations were identified in the raw electron density obtained by EISCAT. The electron density at lower altitudes in the E region (95-115 km) was enhanced by a factor of 3-4 immediately after the optical pulsation became "on."The height-integrated Hall conductance was also elevated, by a factor of 1.5-2, almost in harmony with the electron density variation. The response of the electron density and Hall conductance to the appearance of the pulsating aurora was almost immediate. However, both did not decrease to the background level promptly after optical pulsation ceased. This was primarily because it took a few seconds for the electron density to decrease through recombination with ambient ions at these altitudes. Interestingly, electric field measurements performed by the remote antenna at Kiruna showed that redirection of the electric field occurred when the pulsating aurora was "on." We propose a model in which the enhancement of Hall conductance within patches of the pulsating aurora caused charge accumulation at the edges of the patches, and the electric field was then modified by the resulting polarization electric field. An estimation of the electric field modulation with this model well reproduced the actual electric field observations carried out by EISCAT, which confirmed the validity of the model. These results imply that the ionization caused by high-energy electron precipitation associated with a pulsating aurora has a significant effect on the ionospheric conductivity and current system. This modification of the ionosphere may facilitate characterization of the morphological features of pulsating auroras. In particular, modification of the electric field would affect the spatial structure of pulsating aurora patches, such as their motion and shapes.