Latitudinal dependence of quasi-periodic variations in the geomagnetic field during the greatest geospace storm of September 7-9, 2017

1Chernogor, LF, 1Shevelev, MB
1V.N. Karazin National University of Kharkiv, Kharkiv, Ukraine
Space Sci. & Technol. 2020, 26 ;(2):72-83
Publication Language: Russian
Despite the Solar Cycle 24 minimum in the vicinity, September in 2017 was characterized by high astral activity, when 40 C-class, 15 M-class, and 4 X-class flares occurred. Huge coronal mass ejection events and strong geospace storms, sets of magnetic, ionospheric, and atmospheric storms as well as electric field disturbances, were reported. The purpose of this paper is to present the results of analysis of global-scale quasi-periodic variations in the geomagnetic field during the unique geospace storm that occurred on September 7—9, 2017. To analyze the time variations, the data acquired at the 0.1-nT resolution and the 1-min sampling interval from the Intermagnet magnetometer network at the Tamanrasset (22.79°N, 5.53°E), Duronia (41.35°N, 14.466°E), Lonjsko Polje (45.408°N, 16.659°E), Belsk (51.84°N, 20.79°E), Uppsala (59.903°N, 17.353°E), Abisko (68.358°N, 18.823°E) observatories have been used. The local time variations in the horizontal field components that occurred on September 7—9, 2017 have been analyzed. Band-pass filtering and the system spectral analysis have been performed in the 2–120-min per cycle period range, when the mutually complementary short-time Fourier transform (SFT), the Fourier transform in a sliding window (FTS) with a width adjusted to be equal to a fixed number of harmonic periods, and the wavelet transform (WT) employing the Morlet wavelet as a basis function were used simultaneously.
      T he latitudinal dependence of quasi-periodic disturbances in the horizontal components of the geomagnetic field during the unique geospace storm and on a reference day has been studied. The amplitude, spectral content, and the duration of the disturbances have been determined. The geospace storm has been shown to be accompanied by both the aperiodic and quasi-periodic disturbances in the geomagnetic field. The quasi-periodic variations occur in the 35–55- and 70–110-min per cycle period range. The quasi-periodicity strengthens as the geographic latitude of the magnetic observatory decreases. When the geographic latitude increases from ~20° to ~70°, the amplitude of the disturbances increases from 20 to 1500 nT. The duration of the oscillation trains averages fr om a few ones to ~16 hours on September 8–9, 2017.
Keywords: aperiodic and quasi-periodic disturbances, latitudinal dependence of geomagnetic field variations, magnetic storm, quasi-periodic disturbance parameters, system spectral analysis
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