Abstract. Results of simultaneous TV observations of pulsating auroral patches and ELF-VLF-emissions in the morning sector carried out in SodankylaÈ (Finland) on February 15, 1991 are presented. Auroral pulsating activity was typical having pulsating patches with characteristic periods of about 7 s. Narrow-band hiss emissions and chorus elements at intervals of 0.3±0.4 s formed the main ELF-VLF activity in the frequency range 1.0±2.5 kHz at the same time. The analysis of auroral images with time resolution of 0.04 s allowed perfectly separate analysis of spatial and temporal variations in the auroral luminosity. Mutual correspondence between the behaviour of the luminous auroral patches and the appearance of ELF noise type hiss emissions and VLF chorus trains was found in two intervals chosen for analysis. While the hiss emissions were associated with the appearance of luminosity inside a limited area close to the zenith, the structured VLF emissions were accompanied by rapid motion of luminosity inside the area. The spatial dimension of the pulsating area was about 45±50 km and luminosity propagated inside it with velocity of about 10±12 kms. We discuss a new approach to explain the 5±15 s auroral pulsation based on the theory of¯owing cyclotron maser and relaxation characteristics of ionosphere.

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Abstract. We used the TV auroral observations in Barentsburg (78.05 • N 14.12 • E) in Spitsbergen archipelago, together with the data of the CUTLASS HF radars and the POLAR satellite images to study azimuthal (in the east-west direction) expansion of the high-latitude auroral arcs. It is shown that the east or west edge of the arc moved in the same direction as the convection flow, westward in the premidnight sector and eastward in the post-midnight sector. The velocity of arc expansion was of the order of 2.5 km/s, which is 2-3 times larger than the convection velocity measured in the arc vicinity and 2-3 times smaller than the velocity of the bright patches propagating along the arc. The arc expanded from the active auroras seen from the POLAR satellite around midnight as a region of enhanced luminosity, which might be the auroral bulge or WTS. The pole-or equatorward drift of the arcs occurred at the velocity of the order of 100 m/s that was close to the convection velocity in the same direction. These experimental results can be well explained in terms of the interchange (or flute) instability.

Abstract. Auroral TV observations at Loparskaya, Kola Peninsula, and CRRES energetic electron and proton measurements during a moderate isolated substorm at 2000-2100 UT on February 13, 1991, are compared. The CRRES was at the apogee of orbit 494 in the outer radiation belt near the magnetic equator. CRRES footprint projection estimated by using a Tsyganenko magnetic field model was situated at the same latitudes several degrees eastward of active aurora during the substorm breakup or the intensification. The intensification consists of several activations of 1-min duration, and this fine spatial and temporal structure is important for the conjugacy investigations. It is shown that injected energetic electrons have been accelerated at the same time as one of the auroral activations at the same latitude and approximately the same azimuthal extended region. The lack of enhanced electrons during other activations suggests that the acceleration region has a sharp equatorial boundary.

Abstract. Variation of the luminosity in two parallel auroral arcs before auroral breakup has been studied by using digitised TV-data with high temporal and spatial resolution. The intervals when a new arc appears near already existing one were chosen for analysis. It is shown, for all cases, that the appearance of a new arc is accompanied by fading or disappearance of another arc. We have named these events out-of-phase events, OP. Another type of luminosity variation is characterised by almost simultaneous enhancement of intensity in the both arcs (in-phase event, IP). The characteristic time of IP events is 10±20 s, whereas OP events last about one minute. Sometimes out-of-phase events begin as IP events. The possible mechanisms for OP and IP events are discussed.