Anisotropic Vorticity Within Bursty Bulk Flow Turbulence. Issue 10 (12th October 2020)

• Record Type: Journal Article
• Authors: Zhang, L. Q.; Lui, A. T. Y.; Baumjohann, W.; Wang, Chi; Burch, James L.; Khotyaintsev, Yu. V.
• Is Part Of: Journal of geophysical research. Volume 125:Issue 10(2020)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2020-10-12
• Subjects: BBF -- convective vorticity -- turbulence; Magnetospheric physics -- Periodicals; Space environment -- Periodicals; Cosmic physics -- Periodicals; Planets -- Atmospheres -- Periodicals; Heliosphere (Astrophysics) -- Periodicals; Geophysics -- Periodicals; 523.01
• DOI: 10.1029/2020JA028255
• Languages: English
• ISSNs: 2169-9380

Abstract

Abstract: Utilizing Magnetospheric Multiscale (MMS) observation in the tail plasma sheet, we study the vorticity field (ω = ∇ × V ) of the plasma bulk (convective) velocity within the bursty bulk flow (BBF) in detailed. Two typical events are presented. In the event on 25 June 2017, E y is the main component. In the other event on 6 July 2017, E z is the main component. For both cases, the BBF electric field is dominated by the convective electric field (Ec = − V × B ). Our case studies show clearly the existence of the convective vorticity field within the BBF. The vorticity field has prominent anisotropy (quantified by the anisotropic angle ( θ aa = arctan( ω ⊥ / ω ∥ )). More often, the BBF ω field has stronger perpendicular vorticity ( ω ⊥ ) than the parallel vorticity ( ω ∥ ). The dominance of vorticity by ω ⊥ ‐dominating BBF is confirmed in the statistical sense. In particular, event on 25 June shows the significant evolution of the ion flux energy with the strength of the ω field. The strong ω field corresponds to the ion flux enhancement at high energy (above 10 keV), while the weak ω field corresponds to the ion flux enhancement at medium energy (2–5 keV). Investigation of the subset of channel from fast plasma investigation partial moment measurement reveals that the ion behaviors in the strong and decayed BBFs are distinctly different. The channeled ions form the narrow band distribution in the strong BBF but the multiple‐layer distribution in the weak BBF. Finally, spectrum analysis indicates that the BBF ω ⊥ and ω ∥ have a similar scaling about −2.0 (below 0.2 Hz). Key Points: The vorticity ( ω ) of the plasma bulk velocity within the bursty bulk flow (BBF) mostly is perpendicular Within the BBF, the ion flux energy seems to evolve with the strength of the ω field The spectra of BBF ω ⊥ and ω ∥ have a scaling of about −2.0 (below 0.2 Hz)