Magnetic Hole and Its Resultant Electron Pitch-Angle Distribution at Jupiter
C. Q. Wang ,H. S. Fu ,J. B. Cao ,Z. Wang ,W. D. Fu ,Z. Z. Guo et al
Magnetic hole (MH), sometimes referred to as magnetic bottle, exhibits strong magnetic fields at its neck but weak magnetic fields at its belly. Such structure has been widely reported in the solar wind and the Earth’s magnetosphere, but has not been reported at Jupiter. Here, for the first time, we report two MHs in the Jupiter’s magnetosphere by utilizing measurements of the Juno mission, with one existing in the dawn side and the other existing in the dusk side. We find that the electron pitch-angle distribution inside the MHs can be either cigar-type or pancake-type. The cigar-type distribution probably appears at the belly of the MH, whereas the pancake-type distribution probably appears at the neck. Our analyses of the depression of magnetic fields inside the MHs support such a conjunction. These results have advanced our understanding of the transient structure and its related electron dynamics in the giant planets’ magnetosphere.
Fig. 1. Overview of the MH events measured by Juno on 12 November 2021 and 7 May 2017 (a, b, k, l) The location of Juno in Jupiter-Sun-Orbit (JSO) coordinate, the red and green lines represent the nominal positions of the bow shock and magnetic pileup boundary, respectively. Juno observations of (c, m) total magnetic field B(d, n) X-Y-Z magnetic field components in JSO coordinate (e, o) the electron density (f, p) the electron temperature (g, q) the omnidirectional differential energy fluxes of ions (h, r) the omnidirectional differential energy fluxes of high-energy electrons (i, s) the omnidirectional differential energy fluxes of low-energy electrons (j, t) the pitch angle distribution of electrons (42.3– ~235 keV)
Fig. 2.The total magnetic field B and the electron pitch angle (PA) distributions detected channel by channel (a), (i) Total magnetic field B (b)–(h) The electron PA distributions from 16.1 to 475.1 keV in CaseA (i–p) The electron PA distributions from 9.7 to 475.4 keV in CaseB.
Fig. 3.The phase space density (PSD) plotted as a function of electron energy (a), (d) The omnidirectional PSD as a function of electron energy, during period (01:25:00-01:35:00 UT) in CaseA and (11:34:00-11:36:00 UT) in CaseB where the clear PAD appears. In CaseA, the red line represents Maxwellian model, for fitting electron distributions at the thermal energy range. The green line represents a power law model, for fitting electron distributions at the suprathermal energy range. In CaseB, the blue and red lines represent two Maxwellian models, for fitting electron distributions at the cold energy range and thermal energy range, respectively. The green line represents a power law model, for fitting electron distributions at the suprathermal energy range (b), (e) The field-aligned PSD as a function of electron energy during the same period (c), (f) The perpendicular PSD as a function of electron energy during the same period.
Fig. 4.A cartoon of this event. There exist magnetic holes in the dusk-side and dawn-side of Jupiter’s magnetosphere, in which the cigar distribution appears at the belly and the pancake distribution appears near the neck.
