The unique perspective of Solar Orbiter from its inclined orbit in the high latitude phase should aid in the study of the latitude distribution of gradual and impulsive SEP events close to the Sun. Ulysses measurements in the outer heliosphere (>1 AU) show that the difference in latitude between Ulysses and the associated flare orders both onset times and times to maximum well (Dalla et al. 2003). Sanderson et al. (2003) analyzed the same set of events and found that SEPs either propagate at the highest heliographic latitudes along magnetic field lines and not across them at Ulysses’ position. Since onset delay is not correlated with CME parameters, these authors and Struminsky et al. (2006), conclude that the SEPs either propagate along the distorted magnetic field with large latitudinal excursions (e.g. Fisk 1996) or diffuse across magnetic field lines close to the Sun to reach high latitudes. Wibberenz and Cane (2006) suggested lateral coronal transport via low coronal magnetic loops to explain multi-spacecraft observations including Helios. Thus high latitude measurements of SEPs, plus field line tracking, will be crucial to understanding lateral transport.
We, therefore, need to study the following:
- Propagation at high heliographic latitudes along magnetic field lines vs across them (Sanderson et al., 2003).
- Propagation along the distorted magnetic field with large latitudinal excursions (Struminsky et al., 2006).
- Diffusion across magnetic field lines close to the Sun to reach high latitudes (Dressing et al., 2014).
- Lateral coronal transport via low coronal magnetic loops (Wibberenz and Cane, 2006; Klein et al., 2008).
- Wide angular spread of SEP events. Relative role of cross-field diffusion and shocks (Dresing et al., 2014; Lario et al., 2014; Gomez-Herrero et al., 2015).