Variability of interplanetary shock and associated energetic particle properties as a function of the time window around the shock

TL;DR

This study investigates how the choice of sampling time windows affects the measurement of interplanetary shock and energetic particle properties, revealing optimal durations for representative data and implications for modeling and forecasting.

Contribution

It systematically quantifies the variability of shock and ESP properties with different sampling windows, providing new constraints for accurate shock characterization.

Findings

Shock property variability can be up to 26% depending on sampling window.

Optimal sampling windows are approximately 10-60 minutes for different properties.

ESP spectral indices upstream and downstream are similar, indicating local acceleration.

Abstract

We study the effect of sampling windows on derived shock and associated energetic storm particle (ESP) properties in 296 fast-forward interplanetary shocks using ACE measurements at 1 au between 02/1998 - 08/2013. We vary the time windows from 2-mins to 20-mins for the shock properties and from 2-mins to 540-mins for ESP properties. Variability is quantified by the median absolute deviation (MAD) statistic. We find that the magnetic, density, and temperature compression ratios vary from their median values by 17.03%, 20.05%, 25.91%, respectively; shock speed by 16.26%, speed jump by 45.46%, Alfvenic Mach number by 31.53%, and shock obliquity by 24.25%. Spectral indices in the 2-min to 540-min windows downstream of the shock vary from the median value of 1.79 by 26.05%, and by 30.53% from the 1.70 median value upstream of the shock. Similarity of ESP spectral indices upstream and downstream of the shock suggest that these ESP populations are likely locally accelerated at the shock. Furthermore, we find that for a moving sampling window around the shock, values for the density ratio hold for ~10-mins; the magnetic ratio and shock speed jump hold for ~30-mins, and ~60-mins, respectively. Fixing the upstream window to 2-mins and moving only in the downstream direction, then the density ratio holds for ~60-mins downstream, magnetic ratio for ~30-mins, and the shock speed jump holds for ~110-mins. Beyond these time windows, derived shock properties no longer representative of shock properties. These results provide constraints for modeling and forecasting efforts of shock and ESP-associated properties.