Abstract
Abstract. The knowledge about the relative timing of events during the substorm expansion phase onset is very important for understanding the physics of substorms. In this work ground-based television (TV) imaging technique was used for observations of the first auroral arc brightening near zenith of TV chamber for the case of an isolated substorm. The method of the TV image filtration was used giving the possibility to analyze motion of sub visual auroral arcs. The analysis of the connection between the first auroral arc brightening and the beginning of magnetic disturbance was carried out. It was shown that luminosity disturbance is absent to the pole of breakup arc before the breakup and there exist a delay time between the brightening and start of intense magnetic fluctuations in the Pi1–Pi2 frequency ranges. The results obtained have been compared with predictions of theories of auroral breakup.
Highlights
The problem of isolated substorm breakup onset continues to be one of the main unsolved problems of the physics of the magnetosphere
The gradient filtered keogram, where the arrows show the moments of brightening, makes it possible to enter into details of auroral arc dynamics
The existence of time delay ∼1 min between the first auroral arc brightening and the start of the distortion of the geomagnetic field provides the real constrains to existing theories concerning the substorm expansion phase onset and bright auroral arc formation
Summary
The problem of isolated substorm breakup onset continues to be one of the main unsolved problems of the physics of the magnetosphere. The television (TV) observations at Lovosero observatory (64.1◦ N, 115.5 E, MLT=UT+3 h), belonging to the Polar Geophysical Institute, provide the possibility to analyze the auroral breakup fine structure with a time resolution of 25 frames per second and with a high spatial resolution (∼100 m in the zenith). Preliminary results of such analysis summarized by Kornilov et al (2008a, b) demonstrated different pictures of the auroral breakups. We analyze the disturbances of the magnetic field at the observatory and try to determine the time delay between the first auroral arc brightening and the magnetic disturbances onset
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