Variations in the ratio of particle to magnetic field energy density, as observed by Ulysses/HI-SCALE

Kasotakis, G.; Sarris, E. T.; Marhavilas, P. K.; Sidiropoulos, N.; Trochoutsos, P. C.; Daglis, Ioannis A.

doi:10.1016/s1464-1917(98)00011-7

Cited by 7 publications

(3 citation statements)

References 3 publications

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“…Such periods were associated with energetic particle intensity enhancements associated with the passage of shocks driven by coronal mass ejections (CMEs) or corotating interaction regions (CIRs) as well as with intervals of prominent magnetic depressions (cf. Kasotakis et al 1999;Marhavilas 2012). In this paper we study how common the periods with P EP exceeding P B are at heliocentric distances R∼1 AU.…”

Section: Introductionmentioning

confidence: 99%

Energetic Particle Pressure at Interplanetary Shocks: STEREO-A Observations

Lario,

Decker,

Roelof

et al. 2015

Preprint

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We study periods of elevated energetic particle intensities observed by STEREO-A when the partial pressure exerted by energetic (≥83 keV) protons (P EP ) is larger than the pressure exerted by the interplanetary magnetic field (P B ). In the majority of cases, these periods are associated with the passage of interplanetary shocks. Periods when P EP exceeds P B by more than one order of magnitude are observed in the upstream region of fast interplanetary shocks where depressed magnetic field regions coincide with increases of the energetic particle intensities. When solar wind parameters are available, P EP also exceeds the pressure exerted by the solar wind thermal population (P T H ). Prolonged periods (>12 h) with both P EP >P B and P EP >P T H may also occur when energetic particles accelerated by an approaching shock encounter a region well-upstream of the shock characterized by low magnetic field magnitude and tenuous solar wind density. Quasi-exponential increases of the sum P SU M =P B +P T H +P EP are observed in the immediate upstream region of the shocks regardless of individual changes in P EP , P B and P T H , indicating a coupling between P EP and the pressure of the background medium characterized by P B and P T H . The quasi-exponential increase of P SU M implies a convected exponential radial gradient ∂P SU M /∂r>0 that results in an outward force applied to the plasma upstream of the shock. This force can be maintained by the mobile energetic particles streaming upstream of the shocks that, in the most intense events, drive electric currents able to generate diamagnetic cavities and depressed solar wind density regions.

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Section: Introductionmentioning

confidence: 99%

Energetic Particle Pressure at Interplanetary Shocks: STEREO-A Observations

Lario,

Decker,

Roelof

et al. 2015

Preprint

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“…However, the analysis of energetic particles and magnetic field measurements by the Voyager, Ulysses and ACE Spacecraft (s/c) has shown that in a series of ion events the energy density contained in the superthermal tail of the particle distribution is comparable to or even exceeding that of the magnetic field, creating conditions of high-beta plasma [2,3,4,5]. In a work that is in progress, although some topics have been presented in the conference hosted at Halkidiki in June 2009 [5], we extensively survey and analyze measurements of the energy density ratio of energetic ions to the magnetic field's for the entire Ulysses' trajectory (years 1990-2009), in order to determine periods in the interplanetary space with high values β ep (>1.0).…”

Section: Introductionmentioning

confidence: 99%

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

Marhavilas¹,

Sarris²,

Anagnostopoulos³

2011

AIP Conference Proceedings

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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 β ep ) of the energetic ions' (20 keV to ~5 MeV) to the magnetic field's in order to find occurrences of high-beta (β ep >1) superthermal plasma conditions in the environment of the Jovian magnetosphere, which is an interesting plasma laboratory and an important source of emissions in our solar system. In particular, we examine high-beta ion events close to Jupiter's bow shock, which are produced by two processes: (a) bow shock ion acceleration and (b) ion leakage from the magnetosphere.

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“…In the interplanetary space, the value of beta is usually in the range of 0.1-1.0 [1] and the contribution of the supra-thermal particles to the plasma pressure is generally assumed negligible. However, the analysis of energetic particles and magnetic field measurements by the Voyager, Ulysses and ACE Spacecraft (s/c) has shown that in a series of ion events the energy density contained in the supra-thermal tail of the particle distribution is comparable to or even exceeding that of the magnetic field, creating conditions of high-beta plasma [2], [3], [4], [5], [6]. In this work which is in progress, although some topics have been presented in the conference hosted at Halkidiki in June 2009 [5], we extensively survey and analyze measurements of the energy density ratio of energetic ions to the magnetic field's (parameter β ep ) for the entire Ulysses mission (years 1990-2009), in order to determine periods in the interplanetary space with high values β ep (>1.0).…”

mentioning

confidence: 99%

Study of high-beta supra-thermal plasma events in the vicinity of magneto-hydrodynamic shock-waves

Marhavilas¹,

Sarris²

2010

JESTR

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The ratio value-known as plasma parameter "beta" (β)-of the interplanetary-plasma pressure (thermal pressure) to the magnetic field's (magnetic pressure) or of their energy densities, is critical for the space plasmas and has important consequences to their properties. Although in the scientific literature the contribution of the supra-thermal 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 supra-thermal 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. In particular, in this paper we analyze Ulysses measurements of the energy density ratio (parameter βep) of the supra-thermal (20 keV to ~5 MeV) ions' (by the HI-SCALE instrument) to the magnetic field's (by the VHM/FGM instrument) in order to find occurrences of high-beta (βep >1) supra-thermal plasma conditions in the vicinity of interplanetary shock-waves. These high-beta ion events are associated with energetic particle intensity enhancements which have been produced by reacceleration at the shock fronts.

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Variations in the ratio of particle to magnetic field energy density, as observed by Ulysses/HI-SCALE

Cited by 7 publications

References 3 publications

Energetic Particle Pressure at Interplanetary Shocks: STEREO-A Observations

Energetic Particle Pressure at Interplanetary Shocks: STEREO-A Observations

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

Study of high-beta supra-thermal plasma events in the vicinity of magneto-hydrodynamic shock-waves

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