Abstract
Abstract. Results of simultaneous TV observations of pulsating auroral patches and ELF-VLF-emissions in the morning sector carried out in Sodankylä (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 flowing cyclotron maser and relaxation characteristics of ionosphere.Key words. Magnetospheric physics (auroral phenomena; magnetosphere-ionosphere interactions) · Space plasma physics (wave-particle interactions)
Highlights
It is generally accepted that the whistler mode VLF waves play an important role in precipitation of Correspondence to: V
As shown by Scour®eld and Parsons (1971a) and Kosch and Scour®eld (1992) these types of auroral pulsations can transform from one type to another in a short time interval comparable with a single pulsation period
The ®rst is the existence of aux tube with an enhanced background cold plasma density playing the role of resonator for ELF-VLF waves
Summary
There are dierent types of pulsating aurora observed during post-breakup period. Rùyrvic and Davis (1977) determined the range of spatial dimensions of pulsating patches from 20 to 200 km. Scour®eld et al (1972) studying a spatial coherency of pulsating aurora found that pulsations are coherent at the distances less than 30 km. In this work we will deal with two types of pulsations. The second ones are expanding and propagating pulsations. This type of pulsation begins with initial brightening of a core and the patch expands spatially in one or more directions (Scour®eld and Parsons, 1971a; Thomas and Stenbaek-Nielsen, 1981). The region of expansion or propagation with horizontal dimensions of tens to hundred kilometers usually retain its shape during several periods.
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