Dynamics of He++ ions at interplanetary and Earth's bow shocks

TL;DR

This study analyzes the behavior of He++ ions during interplanetary and Earth's bow shocks using high-resolution satellite data, revealing correlations between helium abundance and shock parameters, and highlighting differences in ion dynamics at various shock types.

Contribution

It provides new insights into the plasma structure and ion parameter variations at interplanetary and Earth's bow shocks using high-resolution measurements from multiple satellites.

Findings

Helium abundance drops behind interplanetary shocks with decreasing { heta}_{Bn}.

Significant increase in helium abundance observed in quasi-perpendicular Earth's bow shocks.

Correlations identified between helium abundance and shock parameters like {eta}_{i} and M_{ms}.

Abstract

Experimental investigations of the fine plasma structure of interplanetary shocks are extremely difficult to conduct due to their small thickness and high speed relative to the spacecraft. We study the variations in the parameters of twice-ionized helium ions (4He++ ions or {\alpha}-particles) in the solar wind plasma during the passage of interplanetary shocks and Earth's bow shock. We use data with high time resolution gathered by the BMSW (Bright Monitor of Solar Wind) instrument installed on the SPEKTR-R satellite, which operated between August 2011 and 2019. The MHD parameters of He++ ions (the bulk velocity Va, temperature Ta, absolute density Na, and helium abundance Na/Np) are analyzed for 20 interplanetary shocks and compared with similar parameters for 25 Earth's bow shock crossings. Measurements from the WIND, Cluster and THEMIS satellites were also analyzed. The correlations in the changes in helium abundance Na/Np with the parameters {\beta}_{i}, {\theta}_{Bn} and M_{ms} were investigated. A correlation between Na/Np and the angle {\theta}_{Bn} was found: the lower the value of {\theta}_{Bn}, the greater the drop in helium abundance Na/Np falls behind the IP shock front. For Earth's bow shock crossings, we found a significant increase in the helium abundance Na/Np in quasi-perpendicular events.