Publications

2016

• Solar wind test of the de Broglie-Proca massive photon with Cluster multi-spacecraft data
  
  • Retinò Alessandro
  • Spallicci Alessandro D. A. M.
  • Vaivads Andris
  Astroparticle Physics, Elsevier, 2016, 82, pp.49–55. Our understanding of the universe at large and small scales relies largely on electromagnetic observations. As photons are the messengers, fundamental physics has a concern in testing their properties, including the absence of mass. We use Cluster four spacecraft data in the solar wind at 1 AU to estimate the mass upper limit for the photon. We look for deviations from Ampère’s law, through the curlometer technique for the computation of the magnetic field, and through the measurements of ion and electron velocities for the computation of the current. We show that the upper bound for mγ lies between 1.4×10−491.4×10−49 and 3.4×10−513.4×10−51 kg, and thereby discuss the currently accepted lower limits in the solar wind. (10.1016/j.astropartphys.2016.05.006)
  DOI : 10.1016/j.astropartphys.2016.05.006
• Distinct responses of the low-latitude ionosphere to CME and HSSWS: The role of the IMF B^z oscillation frequency
  
  • Rodríguez-Zuluaga J.
  • Radicella S. M.
  • Nava B.
  • Amory-Mazaudier Christine
  • Mora-Páez H.
  • Alazo-Cuartas K.
  Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2016. In this work an attempt to identify the role of the interplanetary magnetic field (IMF) in the response of the ionosphere to different solar phenomena is presented. For this purpose, the day-today variability of the equatorial ionospheric anomaly (EIA) and the main ionospheric disturbances are analyzed during one coronal mass ejection (CME) and two high-speed solar wind streams (HSSWSs). The EIA parameters considered are the zonal electric field and both the strength and position of its northern crest. The disturbances being the prompt penetration of magnetospheric electric field (PPMEF) and disturbance dynamo electric field (DDEF) are studied using the magnetic response of their equivalent current systems. In accordance, ground-based Global Navigation Satellite Systems receivers and magnetometers at geomagnetic low latitudes in the American sector are used. During both phenomena, patterns of PPMEF related to fluctuations of the IMF are observed. Diurnal and semidiurnal magnetic oscillations are found to be likely related to DDEF. Comparisons among the EIA parameters and the DDEF magnetic response exhibit poor relation during the CME in contrast to good relation during the HSSWSs. It is concluded that the response of the low-latitude ionosphere to solar phenomena is largely determined through the oscillation frequency of the IMF B z by affecting the generation of the PPMEF and DDEF differently. This is seen as an effect of how the energy from the solar wind is transferred into the magnetosphere-ionosphere system. (10.1002/2016JA022539)
  DOI : 10.1002/2016JA022539
• Equatorial noise emissions with a quasi-periodic modulation observed by DEMETER at harmonics of the O⁺ ion gyrofrequency
  
  • Parrot Michel
  • Nĕmec František
  • Santolík Ondřej
  • Cornilleau-Wehrlin Nicole
  Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2016, 121 (10), pp.10,289–10,302. The analysis of ionospheric equatorial noise (EN) with a quasi-periodic (QP) modulation observed by the DEMETER spacecraft is presented. These EN emissions also called whistler mode or fast magnetosonic waves play an important role in acceleration of radiation belt electrons. A statistical analysis with 103 events shows that they occur just after intense magnetic storms. Usually, they are generated by unstable proton ring distribution close to the magnetic equator at harmonics of the proton gyrofrequency in the inner magnetosphere (2 < L < 8). But at lower L values down in the ionosphere three events have been analyzed and it appears that the EN waves are at harmonics of - or very close to - a O⁺ ion gyrofrequency which can be found close or slightly above the satellite. The wave propagation analysis indicates that these emissions are coming from an area above the satellite. Concerning one event, the EN emissions are observed on several consecutive orbits and there is a temporal coincidence with observations performed by the CLUSTER satellites at higher altitudes in the magnetosphere. EN emissions at lower frequencies have been also observed by the CLUSTER satellites in the same longitudinal sector as DEMETER but at ~5 R_E. The analysis of the STAFF data onboard C1 reveals that the magnetic field spectrogram has peaks close to harmonics of the local proton gyrofrequency as usually reported. It is shown that the DEMETER and CLUSTER EN waves have a similar QP modulation but with slightly different period and frequency. (10.1002/2016JA022989)
  DOI : 10.1002/2016JA022989
• Impact of the Eulerian chaos of magnetic field lines in magnetic reconnection
  
  • Firpo Marie-Christine
  • Ettoumi Wahb
  • Lifschitz A. F.
  • Retinò Alessandro
  • Farengo R F
  • Ferrari H E
  • García-Martínez P L
  Physics of Plasmas, American Institute of Physics, 2016, 23 (12). Stochasticity is an ingredient that may allow the breaking of the frozen-in law in the reconnec-tion process. It will first be argued that non-ideal effects may be considered as an implicit way to introduce stochasticity. Yet there also exists an explicit stochasticity that does not require the invocation of non-ideal effects. This comes from the spatial (or Eulerian) chaos of magnetic field lines that can show up only in a truly three-dimensional description of magnetic reconnection since two-dimensional models impose the integrability of the magnetic field lines. Some implications of this magnetic braiding, such as the increased particle finite-time Lyapunov exponents and increased acceleration of charged particles, are discussed in the frame of tokamak sawteeth that form a laboratory prototype of spontaneous magnetic reconnection. A justification for an increased reconnection rate with chaotic vs integrable magnetic field lines is proposed. Moreover, in 3D, the Eulerian chaos of magnetic field lines may coexist with the Eulerian chaos of velocity field lines, that is more commonly named turbulence. (10.1063/1.4972544)
  DOI : 10.1063/1.4972544
• Ion injection at Quasi-parallel Shocks Seen by the Cluster Spacecraft
  
  • Johlander A.
  • Vaivads A.
  • Khotyaintsev Y. V.
  • Retinò Alessandro
  • Dandouras I.
  The Astrophysical Journal Letters, Bristol : IOP Publishing, 2016, 817 (1), pp.L4. Collisionless shocks in space plasma are known to be capable of accelerating ions to very high energies through diffusive shock acceleration (DSA). This process requires an injection of suprathermal ions, but the mechanisms producing such a suprathermal ion seed population are still not fully understood. We study acceleration of solar wind ions resulting from reflection off short large-amplitude magnetic structures (SLAMSs) in the quasi-parallel bow shock of Earth using in situ data from the four Cluster spacecraft. Nearly specularly reflected solar wind ions are observed just upstream of a SLAMS. The reflected ions are undergoing shock drift acceleration (SDA) and obtain energies higher than the solar wind energy upstream of the SLAMS. Our test particle simulations show that solar wind ions with lower energy are more likely to be reflected off the SLAMS, while high-energy ions pass through the SLAMS, which is consistent with the observations. The process of SDA at SLAMSs can provide an effective way of accelerating solar wind ions to suprathermal energies. Therefore, this could be a mechanism of ion injection into DSA in astrophysical plasmas. (10.3847/2041-8205/817/1/L4)
  DOI : 10.3847/2041-8205/817/1/L4
• Beyond the Maltese Cross: Geometry of Turbulence Between 0.2 and 1 au
  
  • Verdini Andrea
  • Grappin Roland
  The Astrophysical Journal, American Astronomical Society, 2016, 831. The spectral anisotropy of turbulent structures has been measured in the solar wind since 1990, relying on the assumption of axisymmetry about the mean magnetic field, B <SUB>0</SUB>. However, several works indicate that this hypothesis might be partially wrong, thus raising two questions: (i) is it correct to interpret measurements at 1 au (the so-called Maltese cross) in term of a sum of slab and two-dimensional (2D) turbulence; and (ii) what information is really contained in the Maltese cross? We solve direct numerical simulations of the magnetohydrodynamic equations including the transverse stretching exerted by the solar wind flow and study the genuine 3D anisotropy of turbulence as well as that one resulting from the assumption of axisymmetry about B <SUB>0</SUB>. We show that the evolution of the turbulent spectrum from 0.2 to 1 au depends strongly on its initial anisotropy. An axisymmetric spectrum with respect to B <SUB>0</SUB> keeps its axisymmetry, i.e., resists stretching perpendicular to radial, while an isotropic spectrum becomes essentially axisymmetric with respect to the radial direction. We conclude that close to the Sun, slow-wind turbulence has a spectrum that is axisymmetric around B <SUB>0</SUB> and the measured 2D component at 1 au describes the real shape of turbulent structures. In contrast, fast-wind turbulence has a more isotropic spectrum at the source and becomes radially symmetric at 1 au. Such structure is hidden by the symmetrization applied to the data that instead returns a slab geometry. (10.3847/0004-637X/831/2/179)
  DOI : 10.3847/0004-637X/831/2/179