Cluster Observations of a Dispersive Flapping Event of Magnetotail Current Sheet. Issue 7 (27th July 2018)

• Record Type: Journal Article
• Authors: Rong, Z. J.; Cai, Y. H.; Gao, J. W.; Lui, A. T. Y.; Shen, C.; Petrukovich, A. A.; Wei, Y.; Wan, W. X.
• Is Part Of: Journal of geophysical research. Volume 123:Issue 7(2018)
• Page Start: 5571
• Page End: 5579
• Publication Date: 2018-07-27
• Subjects: magnetotail -- plasma sheet -- current sheet -- neutral sheet -- flapping waves -- dispersive properties; Magnetospheric physics -- Periodicals; Space environment -- Periodicals; Cosmic physics -- Periodicals; Planets -- Atmospheres -- Periodicals; Heliosphere (Astrophysics) -- Periodicals; Geophysics -- Periodicals; 523.01
• DOI: 10.1029/2018JA025196
• Languages: English
• ISSNs: 2169-9380

Abstract

Abstract: A kink‐like flapping event of Earth magnetotail current sheet, which consists of two frequency bands successively, is studied by the multipoint observations of Cluster. The multipoint analysis of Cluster observations demonstrates that the higher frequency band (period is about 10 min) has faster propagation velocity (about 30 km/s), shorter wavelength (about 3 RE ), and smaller amplitude (1–1.5 RE ). In contrast, the lower frequency band (period is about 22 min) shows slower propagation velocity (about 21 km/s), longer wavelength (about 4.4 RE ), and larger amplitude (2–3 RE ). Comparison with the flapping models demonstrates that the dispersion of theoretical models does not show consistency with the results of this event, which suggests that new or more advanced kink‐like flapping theories or models in the future have to consider the constraints of the dispersive properties demonstrated by this event. Plain Language Summary: The morphology of the elongated geomagnetic field in the downstream, called as magnetotail, implies presence of a current sheet near equator where magnetic field reverses its direction. Earlier studies demonstrate that the local current sheet often moves or flaps up and down, resulting in multiple crossings of current sheet as observed by spacecraft. As an important dynamic process for releasing the magnetospheric energy, flapping motion has drawn attention increasingly. Observations in the past decade demonstrate that the flapping motion of magnetotail current sheet can propagate from midnight toward both flanks with velocities of a few tens of kilometers per second, but the physics of propagation remains unclear though some theories or models have been presented. Here with a fortunately selected flapping event, which comprises two frequency bands successively observed by Cluster tetrahedron, we showed for the first time that the propagation of flapping waves is dispersive that the flapping waves with higher frequency band have faster propagation velocity, shorter wavelength, smaller amplitude, and vice versa. The revealed dispersion properties are inconsistent with the current models. Thus, new or more advanced flapping theories or models are required in the future considering the constraints of the dispersive properties demonstrated by this study. Key Points: Two different flapping frequency bands are observed successively in a kink‐like flapping event The band with higher frequency has faster propagation velocity and smaller amplitude than that of lower frequency The comparison of current theoretic models fails to show consistency with this event