Development of a formalism for computing transits of Earth-directed CMEs, plasma sheaths, and shocks. Towards a forecasting tool

Abstract

Interplanetary Coronal mass ejections (ICMEs) (super-magnetosonically) faster than the ambient solar wind are preceded by shock waves. Earth-directed shock waves, plasma sheaths and ICMEs are precursors of the major geomagnetic storms. The plasma sheath between the shock and the ICME leading edge plays a very important role to determine the geoeffectiveness of the events. There are multiple efforts (empirical, analytical and numerical) to forecast ICME–shock transit times and arrival speeds to 1AU. We present a formalism (combining analytical and empirical solutions) to compute trajectories of fast halo Earth directed ICMEs, plasma sheaths, and shocks. This formalism combines the ‘piston-shock’ semi-empirical model (Corona-Romero et al., 2013), and the MHD polytropic jump relations (Petrinec and Russell, 1997) to approximate the 1AU plasma sheath and ICME properties. Nine Earth directed ICME–shock cases, including the “Bastille” and “Halloween” events were analyzed. The model obtained compares well with in situ data. Finally, we found a possible empiric relation for the free parameter of our formalism. If this empiric relationship is confirmed, it could turn this formalism into a space weather forecasting tool.