Panagiotis K. Marhavilas

Periodic signals in Ulysses’ energetic particle events upstream and downstream from the Jovian bow shock

Abstract We present results from a statistical analysis of energetic particle events, observed by the Heliosphere instrument for spectra, composition, and anisotrophy at low energies (HI-SCALE) instrument onboard Ulysses, upstream from the bow shock of Jupiter, during the inbound and outbound trajectory of the spacecraft. A harmonic analysis on the intensity time series of 192 distinct 61– 77 keV upstream ion events, suggests a modulation with a period of ∼40 min or ∼15– 20 min in 48% of the total number of events, at the significance level of P=0.05. In some cases, the periodicity is not significant in the ion intensities, while it is significant in the ion anisotropy and/or spectral data. Our analysis shows that the periodic modulation was more frequently observed on the out-of-ecliptic trajectory (67 events), than on the ecliptic trajectory (26 events). An ∼40/15– 20 min periodicity was also found in energetic ion and electron events in the magnetosheath. The results from the statistical analysis of HI-SCALE measurements are consistent with a magnetospheric source for the majority of the upstream events. The statistical results are also consistent with preferential leakage of energetic ions from the south high-latitude Jovian magnetosphere.

Large-scale energetic particle layers in the high latitude Jovian magnetosphere

Abstract This study presents an analysis of long lasting (∼2– 3 h ) energetic (≳60 keV ) ion and (≳40 keV ) electron events observed by the HISCALE instrumentation on board Ulysses in the high latitude Jovian magnetosphere. The high latitude events in the prenoon dayside (d 36–38, 1992) and the south duskside (d 40–43, 1992) magnetosphere are different from the magnetodisk plasma sheet events; they are characterized by: (a) a rigidity dependent flux dispersion, (b) softening of the spectrum of energetic ions and electrons at flux minima (and of low energy ions at flux maxima) and (c) proximity of the spacecraft to the high latitude magnetopause. The spectral index peaks which correspond to the high latitude particle events show a ∼10 h (or ∼5 h ) periodicity and a phase shift of ∼7 h between the inbound and the outbound measurements. The HISCALE data are consistent with the existence of large scale layers of energetic ions and electrons in the high latitude Jovian magnetosphere. The proposed concept of the high latitude magnetospheric large scale energetic particle layers provide us with the possibility of a new synthesis of a variety of Jovian observations.

Energetic ion (>∼50keV) and electron (>∼40keV) bursts observed by Ulysses near Jupiter

Abstract A careful analysis of data collected by the HISCALE experiment on board Ulysses suggests that the quasi-periodic (QP) modulation of several or tens of minutes in flux and/or anisotropy/spectral observations is an almost permanent characteristic of the energetic (>∼50 keV) ion population in the outer and the high latitude middle magnetosphere of Jupiter. In most cases a periodicity of ∼5–20 min is evident, although periodicities of ∼40 min and ∼80 min were also observed. The ∼40 min and ∼80 min periodicities were often accompanied by other harmonics, for instance ∼20 min and ∼40 min periodicities respectively, and were preferentially observed in the dusk magnetosphere. Observations of QP series of energetic ion and electron bursts in the dusk high latitude magnetosphere, as for instance, strong anisotropy, forward velocity dispersion and time delay between the ion and the electron onsets, are consistent with a periodic acceleration / injection of particles, in the form of field-aligned beams, originated from the low altitude environment of the planet (∼8 R J from the planet surface); the QP intensity gradients perpendicular to the field observed in the dusk middle magnetosphere are consistent with spatial structures of energetic particle sheets crossed by the spacecraft. The QP bursts of energetic particles are often accompanied by bursts of radio and aurora emissions and are possible sources of these Jovian phenomena.

Distinct shock acceleration processes — Evaluation of the magnetic trap dimensions formed upstream of an interplanetary shock using measurements of the ulysses spacecraft

Abstract We analyze the acceleration signatures of energetic ions (E > 50 keV) and electrons (E > 30 keV) being observed on day 256 of the year 1992 UT, in the vicinity of the surface of a fast-mode quasi-perpendicular interplanetary hydromagnetic shock, using fine time resolution measurements by the HI-SCALE instrument onboard the Ulysses spacecraft,(s/c). The observations present strong evidence for the acceleration of energetic particles trapped within magnetic structures on the surface of the fast-mode shock. We discuss the flux-times profiles and particle distributions near the shock in the context of previous theoretical studies and models. Moreover we are in the procedure of evaluating the width L and amplitude A of the magnetic structure by using HI-SCALE measurements and a sinusoidal form geometry.

Survey of High-Beta Superthermal Plasma Events in the Interplanetary Medium as Observed by Ulysses Throughout its Mission Lifetime (1990–2009)

The ratio of the plasma pressure to the magnetic field pressure (or the ratio of their energy densities)-plasma parameter “beta” (β)-is critical in determining the dynamics of the interaction of the solar wind with planetary magnetospheres and has important implications to the propagation of energetic particles and to the structure of the shocks. In the interplanetary space, the value of “beta” is usually in the range of 0.1-1.0, and the contribution of the superthermal particles to the plasma pressure is generally assumed negligible. However, the analysis of energetic particles and magnetic field measurements by the Ulysses spacecraft shows that, in a series of events, the energy density contained in the superthermal tail of the particle distribution is comparable to or even higher than the one of the magnetic field, creating conditions of high-beta plasma. In this paper, we extensively survey and analyze measurements of the energy density ratio (parameter ) of the energetic particles (20 keV-5 MeV) to the magnetic fields by Ulysses, for its entire trajectory (1990-2009), in order to find occurrences of high-beta (βep >; 1) superthermal plasma conditions. As expected, periods of dominant magnetic energy were observed most of the time, for the above mentioned particle energy range. Nevertheless, a number of 484 distinct periods with a total duration of 406.02 days were identified when the energy density carried by the energetic ions overwhelmingly dominated that of the magnetic field. These interplanetary high-beta (βep >; 1) events are characterized by a very high parameter (up to ~1733), a great total duration (of 406.02 days), and a large percentage (11.3%) of the total mission lifetime (in presence of energetic particle events). Furthermore, these events were detected within well-identified regions corresponding mainly to the following: 1) the vicinity of shock fronts; 2) the vicinity of large transient disturbances associated with shock waves; 3) filamentary magnetic structures; and 4) the vicinity of the Jovian magnetospheric environment. These events were also associated with energetic particle intensity enhancements due to the following: 1) reacceleration at interplanetary corotating interaction regions (CIRs), solar flare (blast), transient, and/or CME-driven shocks; 2) unusually large magnetic field depressions; 3) Jupiters bow shock particle acceleration; and 4) leakage from Jupiters magnetosphere.

Occurrence of high-beta superthermal plasma events in the close environment of Jupiter's bow shock as observed by Ulysses

The ratio of the plasma pressure to the magnetic field pressure (or of their energy densities) which is known as the plasma parameter “beta” (β) has important implications to the propagation of energetic particles and the interaction of the solar wind with planetary magnetospheres. Although in the scientific literature the contribution of the superthermal particles to the plasma pressure is generally assumed negligible, we deduced, by analyzing energetic particles and magnetic field measurements recorded by the Ulysses spacecraft, that in a series of events, the energy density contained in the superthermal tail of the particle distribution is comparable to or even higher than the energy density of the magnetic field, creating conditions of high‐beta plasma. More explicitly, in this paper we analyze Ulysses/HI‐SCALE measurements of the energy density ratio (parameter βep) of the energetic ions’ (20 keV to ∼5 MeV) to the magnetic field’s in order to find occurrences of high‐beta (βep>1) superthermal plasma ...