Coronal shocks properties and their associations with energetic particle events measured near 1AU.

Abstract:

We combine ultraviolet and white-light images obtained by the Solar Dynamics Observatory (SDO) and the Solar-Terrestrial Relations Observatory (STEREO) to track, in the lower corona, the spatial and temporal evolution of pressure waves and shocks associated with the onset of Coronal Mass Ejections (CMEs). We use ideal geometrical 3-D surfaces to follow with time the location of the global disturbance observed in EUV and white-light images. This fitting technique provides a tracking of the evolution of shocks from the Sun to 20 solar radii.

We combine potential field source surface calculations with simple models of the distribution of interplanetary magnetic field lines in the interplanetary medium to determine the magnetic connectivity of the shock with spacecraft located near 1AU. We extract the 3-D shock velocity vector, the shock geometry and, by using empirical functions of temperature and density variations in the corona, the local Alfven speed at the point of magnetic connectivity with STEREO-A, STEREO-B and L1 spacecraft.

The properties of the tracked coronal shocks are compared with the properties of SEPs measured in situ. We concentrate on the proton-rich events detected by the near-Earth spacecraft as well as the STEREO spacecraft from 2011 to 2014. We use the onset of solar energetic particle events (SEPs) to determine their release time near the Sun. We show that the shock speed at the point of magnetic connectivity is a determining factor for the intensity of the SEP measured in situ with a steep relation between coronal shock speed and SEP maximum intensity. This analysis naturally removes projection effects associated with single viewpoint analysis presented in previous studies. We discuss how the interplay between the radial dependence of the Alfven speed and the complex topology of magnetic field lines in the corona is likely to control the onset time of SEPs at 1AU. We discuss the successes and challenges faced when interpreting SEP events in terms of the speed and geometry of coronal shocks.