Diffusion plays a significant role in the transport of charged, energetic particles in the heliosphere, whether these be galactic cosmic rays (e.g., Engelbrecht 2019; Shen et al. 2019; Moloto & Engelbrecht 2020), solar energetic particles (e.g., Strauss et al. 2017; van den Berg et al. 2021), or Jovian electrons (e.g., Ferreira et al. 2001; Vogt et al. 2020). As such, the diffusion of such particles parallel and perpendicular to the heliospheric magnetic field (HMF) has attracted considerable interest over the years, with various theoretical models for these quantities being proposed, ranging from the quasilinear theory (QLT) of Jokipii (1966), to the nonlinear guiding center (NLGC) theory of Matthaeus et al. (2003) and various recent theories (see, e.g., Shalchi 2010; Ruffolo et al. 2012; Qin & Zhang 2014), which have in turn been applied in various particle transport studies (e.g., Florinski & Pogorelov 2009; Engelbrecht & Burger 2015; Qin & Shen 2017; Moloto et al. 2018; Engelbrecht & Moloto 2021). These theoretical advances have benefited from new insights into particle diffusion via two separate avenues of research, both involving numerical simulations, as particle diffusion coefficients cannot be directly observed. One avenue of research involves numerical test particle simulations of particle diffusion coefficients in the presence of synthetically generated magnetic turbulence, in the process of gaining new insights as to the behavior of these particles, in particular, turbulence scenarios corresponding to a greater or lesser degree with what is observed in the solar wind (see, e.g., Minnie et al. 2007a; Ruffolo et al. 2008; Tautz & Shalchi 2011; Dalena et al.2012; Kong et al. 2017; Mertsch 2020). The other avenue for insights into the diffusion coefficients of charged particles involves the simulation of their transport in the heliosphere. Such studies report on the transport parameters needed as inputs for transport models to ensure agreement between computed particle intensities and various in situ spacecraft observations of the same. These approaches are by no means incompatible, as results from numerical test particle simulations have been shown to be in agreement with those yielded by transport modeling studies (Tautz & Shalchi 2013). The present study follows the latter avenue of inquiry, focusing in particular on the transport of Jovian electrons. In a sense, these particles are the ideal candidates for such a study, as the transport of low-energy electrons in the inner heliosphere has long been known to be negligibly influenced by drift effects (see, e.g., Ferreira et al. 2001; Engelbrecht & Burger 2010; Engelbrecht et al. 2017). Furthermore, the relative orbital motions of the Earth and Jupiter across the Parker (1958) HMF, coupled with the relative abundance of electron observations at 1 au as well as the Jovian source, allows one to compare computed intensities with observations taken during periods of good and bad magnetic connectivity with the source. This, then, allows for the simultaneous study of the transport coefficients of these electrons both parallel and perpendicular to the HMF, which is the aim of this study.
Citation: Qin & Shen 2017
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