Distribution of energetic oxygen and hydrogen in the near-Earth plasma sheet

TL;DR

This study analyzes 7 years of Cluster satellite data to map energetic oxygen and proton distributions in the near-Earth plasma sheet, revealing how geomagnetic and solar wind conditions influence ion behavior and asymmetries.

Contribution

It provides detailed statistical distributions of energetic oxygen and protons, highlighting their responses to geomagnetic activity and solar wind parameters, which was not previously characterized in such detail.

Findings

Energetic oxygen shows stronger dawn-dusk asymmetry than protons.

Southward IMF correlates with significant oxygen acceleration in the tail plasma sheet.

Proton intensities increase on the duskside during disturbed conditions and high dynamic pressure.

Abstract

The spatial distributions of different ion species are useful indicators for plasma sheet dynamics. In this statistical study based on 7 years of Cluster observations, we establish the spatial distributions of oxygen ions and protons at energies from 274 to 955 keV, depending on geomagnetic and solar wind (SW) conditions. Compared with protons, the distribution of energetic oxygen has stronger dawn-dusk asymmetry in response to changes in the geomagnetic activity. When the interplanetary magnetic field (IMF) is directed southward, the oxygen ions show significant acceleration in the tail plasma sheet. Changes in the SW dynamic pressure ($\mathit{P}_{dyn}$) affect the oxygen and proton intensities in the same way. The energetic protons show significant intensity increases at the near-Earth duskside during disturbed geomagnetic conditions, enhanced SW $\mathit{P}_{dyn}$, and southward IMF, implying there location of effective inductive acceleration mechanisms and a strong duskward drift due to the increase of the magnetic field gradient in the near-Earth tail. Higher losses of energetic ions are observed in the dayside plasma sheet under disturbed geomagnetic conditions and enhanced SW $\mathit{P}_{dyn}$. These observations are in agreement with theoretical models.