Investigation Of Superdiffusive Energetic Particle Transport Ahead Of Traveling Shocks

We investigated the connection between the shape of energetic particles'time-intensity profiles ahead of collisionless interplanetary shocks driven by coronalmass ejections and anomalous diffusion. Three strong shocks were recently studied byZimbardo, Prete, and Perri (2020). They found mostly superdiffusive behaviorcharacterized by: (i) More energetic particles are more superdiffusive and, (ii) energeticparticles ahead of shocks with larger shock normal angles ( ) are less superdiffusive. To investigate these results further, the ACE spacecrafts EPAM Level 2 5-minuteaveraged data (Caltech) of 44 strong shock events from 1998-2004 was analyzed. Wemainly focused on the LEMS30 spectrometer data, but LEMS120 data was used as areplacement for entire energy levels where data was significantly incomplete/corrupted.The shock events we investigated were selected based on information about shockevents in the Database of Heliospheric Shock Waves (ipshocks.fi). By fitting atheoretical solution for energetic particle superdiffusive transport ahead of shocks interms of a Mittag-Leffler function to the time-intensity profiles in the interval of 30 to400 minutes ahead of the shock, we estimated the fractional index for anomalousdiffusion that varies between =1 (extreme superdiffusion) and =2 (normal diffusion).We confirm superdiffusive behavior ahead of the vast majority of shock events whilesome exhibit normal diffusion. Contrary to what was previously hypothesized, we donot find any significant correlation between the level of superdiffusion , and or particle energy. No correlation was found between and the value of the anomalousdiffusion coefficient K, magnetic field or proton density shock ratio, Alfven ormagnetosonic Mach numbers. However, we detected a weak correlation betweenaverage and average K, and a high correlation between and K/Avg K. Theinterpretation of the latter is difficult given that K itself depends on .