Dynamics of magnetic structures during the magnetospheric substorm
|1Petrenko, BA, 1Kozak, LV |
1Taras Shevchenko National University of Kyiv, Kyiv, Ukraine
|Kinemat. fiz. nebesnyh tel (Online) 2020, 36(5):55-63|
|Start Page: Dynamics and Physics of Bodies of the Solar System|
The Earth’s magnetosphere and the ambient interplanetary environment can create favorable conditions for the nonlinear process generation of energy release in the form of changes in the topology of the magnetic field and current systems, particle acceleration, wave generation and sharp parameter gradients, which are inherent to a substorm phenomenon. Initially, early studies substantiated the importance of changing the solar wind parameters as a key factor responsible for the beginning of a magnetosphericsubstorm, but later it was shown that this factor is not decisive. Over several decades, continuously improving methods for designing measurement tools and analyzing data helped to identify and conduct a qualitative and quantitative description of the processes that accompany this phenomenon. However, there is no consensus in understanding the scenario of substorm development stepwise. The purpose of the research is to determine the propagation and orientation features of transients (fronts) in the current layer of the Earth’s magnetosphere tail during a substorm. To do this, the magnetic field measurements obtained by the four spacecraft of the Cluster II mission for July 20, 2013 are analyzed. During this event, spacecraft were located on the night side of the Earth’s magnetosphere and recorded changes in the geomagnetic field during the magnetosphere substorm. We used the single-spacecraft method for finding the minimum variance of the magnetic field and multi-spacecraft timing analysis involving cross-correlation of time series. The first method allows finding the normal direction to the structure under study, and the second to find the direction and absolute value of its propagation velocity. The results of the study show that with the development of substorms, for fronts whose movement is moving towards the Earth, a decrease in the propagation velocity and a significant degree of curvature are observed. The first effect (a decrease in the propagation velocity of the fronts) indicates a decrease in the energy reserve of the current sheet for the generation of such transients, and the second effect (a significant degree of curvature) indicates the azimuthal localization of the front.
|Keywords: Earth magnetosphere, minimum variance analysis, plasma discontinuities, substorm|
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