Observations of an Electron-cold Ion Component Reconnection at the Edge of an Ion-scale Antiparallel Reconnection at the Dayside Magnetopause

TL;DR

This paper presents in situ observations of a secondary magnetic reconnection at Earth's magnetopause, highlighting the significant role of cold ions and electrons in the process and their impact on solar wind-magnetosphere coupling.

Contribution

It provides the first observational evidence of cold ions dominating secondary reconnection at the magnetopause edge, revealing their influence on reconnection dynamics.

Findings

Cold ions dominate secondary reconnection at the magnetopause edge.

Cold ions and electrons are accelerated and heated during reconnection.

Simultaneous antiparallel and component reconnection observed.

Abstract

Solar wind parameters play a dominant role in reconnection rate, which controls the solar wind-magnetosphere coupling efficiency at Earth's magnetopause. Besides, low-energy ions from the ionosphere, frequently detected on the magnetospheric side of the magnetopause, also affect magnetic reconnection. However, the specific role of low-energy ions in reconnection is still an open question under active discussion. In the present work, we report in situ observations of a multiscale, multi-type magnetopause reconnection in the presence of low-energy ions using NASA's Magnetospheric Multiscale data on 11 September 2015. This study divides ions into cold and hot populations. The observations can be interpreted as a secondary reconnection dominated by electrons and cold ions located at the edge of an ion-scale reconnection. This analysis demonstrates a dominant role of cold ions in the secondary reconnection without hot ions' response. Cold ions and electrons are accelerated and heated by the secondary process. The case study provides observational evidence for the simultaneous operation of antiparallel and component reconnection. Our results imply that the pre-accelerated and heated cold ions and electrons in the secondary reconnection may participate in the primary ion-scale reconnection affecting the solar wind-magnetopause coupling and the complicated magnetic field topology affect the reconnection rate.