Solar Wind Suprathermal Electrons

mardi 24 septembre 2019, par Linghua Wang (Peking University)

Mardi 1er octobre 2019 à 11h00 , Lieu : Salle de conférence du Château (bât. 9)

Solar wind surpathermal particles carry important information on the common particle acceleration/transport processes at the Sun and in the IPM. We present a statistical survey of solar wind suprathermal electrons measured at 0.1-200 keV by the WIND 3DP instrument at 1 AU during quiet times in solar cycles 23 and 24. All the strahl, halo and superhalo electron populations show no obvious correlation with the solar wind core population. The halo electron population has an isotropic angular distribution, while the strahl population, predominantly observed in fast solar wind, is antisunward beaming along the interplanetary magnetic field. The observed energy spectrum of both strahl and halo electrons at 0.1-1.5 keV generally fits to a Kappa distribution function, with an index κ and effective temperature Teff. We find a strong positive correlation between κ and Teff for both strahl and halo electrons and a strong positive correlation between the strahl density and halo density, likely reflecting the nature of the generation of these electron populations. In addition, the strahl electron number density appears to positively correlate with both the solar wind electron temperature and the IMF magnitude, in both slow and fast solar wind. For the superhalo electron population at quiet times, the observed pitch-angle distribution is generally isotropic, and the observed omnidirectional differential flux generally fits to a power-law function, J  E-β. The spectral index β ranges from 1.6 to 3.7, with a broad maximum between 2.4 and 2.8 (2.0 and 2.4) in solar cycle 23 (24). Both β and nsup show no obvious correlation with the sunspot number, solar flares, CMEs, strahl/halo parameters, etc. In the end, we will talk about the in situ electron acceleration of solar wind suprathermal electrons at ICME-driven shocks observed at 1 AU.

Séminaire donné dans le cadre du consortium meeting de Solar Orbiter/RPW.