Articles | Volume 34, issue 4
Ann. Geophys., 34, 399–409, 2016
https://doi.org/10.5194/angeo-34-399-2016
Ann. Geophys., 34, 399–409, 2016
https://doi.org/10.5194/angeo-34-399-2016

Regular paper 12 Apr 2016

Regular paper | 12 Apr 2016

Statistical analysis of magnetotail fast flows and related magnetic disturbances

Dennis Frühauff and Karl-Heinz Glassmeier Dennis Frühauff and Karl-Heinz Glassmeier
  • Institut für Geophysik und extraterrestrische Physik, Braunschweig, Germany

Abstract. This study presents an investigation on the occurrence of fast flows in the magnetotail using the complete available data set of the THEMIS spacecraft for the years 2007 to 2015. The fast flow events (times of enhanced ion velocity) are detected through the use of a velocity criterion, therefore making the resulting database as large as almost 16 000 events. First, basic statistical findings concerning velocity distributions, occurrence rates, group structures are presented. Second, Superposed Epoch Analysis is utilized to account for average profiles of selected plasma quantities. The data reveal representative time series in near and far tail of the Earth with typical timescales of the order of 1–2 min, corresponding to scale sizes of 3 RE. Last, related magnetic field disturbances are analyzed. It is found that the minimum variance direction is essentially confined to a plane almost perpendicular to the main flow direction while, at the same time, the maximum variance direction is aligned with flow and background field directions. The presentation of the database and first statistical findings will prove useful both as input for magneto-hydrodynamical simulations and theoretical considerations of fast flows.

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Short summary
This study presents an investigation on the occurrence of fast flows in the magnetotail using the complete available data set of the THEMIS spacecraft for the years 2007 to 2015. First, basic statistical findings concerning velocity distributions, occurrence rates, group structures and key features of 16 000 events are presented using Superposed Epoch and Minimum Variance Analysis techniques.