Magnetosphere Dynamics During the 14 November 2012 Storm Inferred from TWINS, AMPERE, Van Allen Probes, and BATS-R-US-CRCM

During the 14 November 2012 geomagnetic storm, the Van Allen Probes spacecraft observed a number of sharp decreases ('dropouts') in particle fluxes for ions and electrons of different energies. In this paper, we investigate the global magnetosphere dynamics and magnetosphere- ionosphere (M-I) coupling during the dropout events using multipoint measurements by Van Allen Probes, TWINS, and AMPERE together with the output of the two-way coupled global BATS-R-US-CRCM model. We find different behavior for two pairs of dropouts. For one pair, the same pattern was repeated: (1) weak nightside Region 1 and 2 Birkeland currents before and during the dropout; (2) intensification of Region 2 currents after the dropout; and (3) a particle injection detected by TWINS after the dropout. The model predicted similar behavior of Birkeland currents. TWINS low-altitude emissions demonstrated high variability during these intervals, indicating high geomagnetic activity in the near-Earth tail region. For the second pair of dropouts, the structure of both Birkeland currents and ENA emissions was relatively stable. The model also showed quasi-stationary behavior of Birkeland currents and simulated ENA emissions with gradual ring current buildup. We confirm that the first pair of dropouts was caused by large-scale motions of the OCB (open-closed boundary) during substorm activity. We show the new result that this OCB motion was associated with global changes in Birkeland (M-I coupling) currents and strong modulation of low-altitude ion precipitation. The second pair of dropouts is the result of smaller OCB disturbances not related to magnetospheric substorms. The local observations of the first pair of dropouts result from a global magnetospheric reconfiguration, which is manifested by ion injections and enhanced ion precipitation detected by TWINS and changes in the structure of Birkeland currents detected by AMPERE. This study demonstrates that multipoint measurements along with the global model results enable the reconstruction of a more complete system-level picture of the dropout events and provides insight into M-I coupling aspects that have not previously been investigated

Electron and ion particle acceleration regimes observed by Juno over Jupiter's main aurora

Over Jupiter's most intense main aurora, the Juno spacecraft has identified up to four different particle acceleration regimes at energies above 30 keV. Some of these regimes are very different than any of the particle acceleration regimes observed over Earth's auoras. We explore here the relationships between these different regimes and their similarities and differences to those at Earth. <P /

Implications of Juno energetic particle observations over Jupiter’s polar regions for understanding magnetosphere-ionosphere coupling at strongly magnetized planets

Juno obtained low altitude space environment measurements over Jupiter’s poles on 27 August 2016 and then again on 11 December 2016. Particle distributions were observed over the poles within the downward loss cones sufficient to power nominally observed auroral emissions and with the characteristic energies anticipated from remote spectroscopic ultra-violet auroral imaging. However, the character of the particle distributions apparently causing the most intense auroral emissions were very different from those that cause the most intense aurora at Earth and from those anticipated from prevailing models of magnetosphere-ionosphere coupling at Jupiter. The observations are highly suggestive of a predominance of a magnetic field-aligned stochastic acceleration of energetic auroral electrons rather than the more coherent acceleration processes anticipated. The Juno observations have similarities to observations observed at higher altitudes at Saturn by the Cassini mission suggesting that there may be some commonality between the magnetosphere-ionosphere couplings at these two giant planets. Here we present the Juno energetic particle observations, discuss their similarities and differences with published observations from Earth and Saturn, and deliberate on the implications of these finding for general understanding of magnetosphere-ionosphere coupling processes

Particle energization and structuring of Jupiter’s main auroral oval as diagnosed with Juno measurements of (>30 keV) energetic particles

Juno polar low-altitude energetic particle observations indicate that the most intense emissions from Jupiter’s main auroral oval are caused by the impingement onto the atmosphere of relatively flat, energy-monotonic electron distributions, often extending to energies >1 MeV. They can be associated with bi-directional angular beaming with upward fluxes greater than the downward fluxes. Downward fluxes of >800 mW/m^2 have been observed. However, when viewed in high time resolution ( 1.0s) these distributions are sometimes (3 of 8)) intermixed with >50keV downward accelerated electron distributions with the classic inverted-V configuration, indicative of steady magnetic field-aligned electric fields. The highest downward energy peak observed so far is 400 keV. The inverted-V energy distributions lack the high energy tails observed in adjacent regions, and thus, contrary to what is observed at Earth, the associated downward energy fluxes are generally lower than the downward energy fluxes associated with the more intense energy-monotonic distributions. The relationship between these two modes of auroral particle energization is unclear. Do the classic auroral processes that create inverted-V distributions become so powerful that instabilities are stimulated that cause stochastic energization to turn on and dominate, or do these two different forms of auroral acceleration represent distinctly different processes? These and other questions are explored

Particle energization and structuring of Jupiter’s main auroral oval as diagnosed with Juno measurements of (>30 keV) energetic particles

Juno polar low-altitude energetic particle observations indicate that the most intense emissions from Jupiter’s main auroral oval are caused by the impingement onto the atmosphere of relatively flat, energy-monotonic electron distributions, often extending to energies >1 MeV. They can be associated with bi-directional angular beaming with upward fluxes greater than the downward fluxes. Downward fluxes of >800 mW/m^2 have been observed. However, when viewed in high time resolution ( 1.0s) these distributions are sometimes (3 of 8)) intermixed with >50keV downward accelerated electron distributions with the classic inverted-V configuration, indicative of steady magnetic field-aligned electric fields. The highest downward energy peak observed so far is 400 keV. The inverted-V energy distributions lack the high energy tails observed in adjacent regions, and thus, contrary to what is observed at Earth, the associated downward energy fluxes are generally lower than the downward energy fluxes associated with the more intense energy-monotonic distributions. The relationship between these two modes of auroral particle energization is unclear. Do the classic auroral processes that create inverted-V distributions become so powerful that instabilities are stimulated that cause stochastic energization to turn on and dominate, or do these two different forms of auroral acceleration represent distinctly different processes? These and other questions are explored