Characteristics of ion distribution functions in dipolarizing flux bundles: Event studies. Issue 6 (1st June 2017)

• Record Type: Journal Article
• Authors: Runov, A.; Angelopoulos, V.; Artemyev, A.; Birn, J.; Pritchett, P. L.; Zhou, X.‐Z.
• Is Part Of: Journal of geophysical research. Volume 122:Issue 6(2017)
• Page Start: 5965
• Page End: 5978
• Publication Date: 2017-06-01
• Subjects: magnetotail dynamics -- dipolarizations -- bursty bulk flows -- particle energization -- distribution functions; Magnetospheric physics -- Periodicals; Space environment -- Periodicals; Cosmic physics -- Periodicals; Planets -- Atmospheres -- Periodicals; Heliosphere (Astrophysics) -- Periodicals; Geophysics -- Periodicals; 523.01
• DOI: 10.1002/2017JA024010
• Languages: English
• ISSNs: 2169-9380

Abstract

Abstract: Taking advantage of multipoint observations from a repeating configuration of the five Time History of Events and Macroscale Interactions during Substorms (THEMIS) probes separated by 1 to 2 Earth radii ( R E ) along X, Y, and Z in the geocentric solar magnetospheric system (GSM), we study ion distribution functions collected by the probes during three dipolarizing flux bundle (DFB) events observed at geocentric distances 9 < R < 14 R E . By comparing these probes' observations, we characterize changes in the ion distribution functions with respect to probe separation along the X and Y GSM directions and | B x | levels, which characterize the distance from the neutral sheet. We found that the characteristics of the ion distribution functions strongly depended on the | B x | level, whereas changes with respect to X and Y were minor. In all three events, ion distribution functions f (v ) observed inside DFBs were organized by magnetic and electric fields. The probes near the magnetic equator observed perpendicular anisotropy of the phase space density in the range between thermal energy and twice the thermal energy, although the distribution in the ambient plasma sheet was isotropic. The anisotropic ion distribution in DFBs injected toward the inner magnetosphere may provide the free energy for waves and instabilities, which are important elements of particle energization. Key Points: Ion velocity distribution functions f (v ) in three DFB events in the near‐Earth plasma sheet were studied Thermal and suprathermal ions were quasi‐adiabatic ( κ > 1) in DFBs; f (v ) were organized by magnetic field Perpendicular anisotropy of ions at energies E th < E < 2 E th ( E th is thermal energy) was observed in all three events near magnetic equator