Statistical study of particle acceleration in the core of foreshock transients

TL;DR

This study statistically analyzes how foreshock transients upstream of Earth's bow shock can accelerate particles, revealing electron energization and conditions influencing ion and electron energization related to solar wind parameters.

Contribution

It provides the first comprehensive statistical analysis of ion and electron energization within foreshock transients, highlighting internal acceleration processes and formation conditions.

Findings

Electrons are typically energized within foreshock transients.

Ion energies often decrease but can also show enhancements indicating internal acceleration.

Formation conditions are linked to weak magnetic fields and fast solar wind.

Abstract

Several types of foreshock transients upstream of Earth's bow shock possessing a tenuous, hot core have been observed and simulated. Because of the low dynamic pressure in their cores, these phenomena can significantly disturb the bow shock and the magnetosphere-ionosphere system. Recent observations have also demonstrated that foreshock transients can accelerate particles which, when transported earthward, can affect space weather. Understanding the potential of foreshock transients to accelerate particles can help us understand shock acceleration at Earth and at other planetary and astrophysical systems. To further investigate foreshock transients' potential for acceleration we conduct a statistical study of ion and electron energization in the core of foreshock transients. We find that electron energies typically increase there, evidently due to an internal acceleration process, whereas, as expected, ion energies most often decrease to support transient formation and expansion. Nevertheless, ion energy enhancements can be seen in some events suggesting an internal ion acceleration process as well. Formation conditions of foreshock transients are related to weak solar wind magnetic field strength and fast solar wind speed. Ion and electron energization are also positively correlated with solar wind speed.