Study of reconnection-associated multi-scale fluctuations with Cluster and Double Star

TL;DR

This study analyzes multi-scale magnetic fluctuations during reconnection events at Earth’s magnetosphere using data from Cluster and Double Star spacecraft, revealing asymmetries and turbulence characteristics in outflow regions.

Contribution

It provides a comparative analysis of spectral scaling and anisotropy in reconnection outflows, highlighting asymmetries and turbulence features in different regions.

Findings

Tailward outflow shows MHD cascading turbulence features.

Earthward outflow exhibits more power and larger anisotropy angles.

Asymmetry in physical processes between Earthward and tailward regions is confirmed.

Abstract

The objective of the paper is to asses the specific spectral scaling properties of magnetic reconnection associated fluctuations/turbulence at the Earthward and tailward outflow regions observed simultaneously by the Cluster and Double Star (TC-2) spacecraft on September 26, 2005. Systematic comparisons of spectral characteristics, including variance anisotropy and scale-dependent spectral anisotropy features in wave vector space were possible due to the well-documented reconnection events, occurring between the positions of Cluster (X = -14--16 $R_e$) and TC-2 (X = -6.6 $R_e$). Another factor of key importance is that the magnetometers on the spacecraft are similar. The comparisons provide further evidence for asymmetry of physical processes in Earthward/tailward reconnection outflow regions. Variance anisotropy and spectral anisotropy angles estimated from the multi-scale magnetic fluctuations in the tailward outflow region show features which are characteristic for magnetohydrodynamic cascading turbulence in the presence of a local mean magnetic field. The multi-scale magnetic fluctuations in the Earthward outflow region are exhibiting more power, lack of variance and scale dependent anisotropies, but also having larger anisotropy angles. In this region the magnetic field is more dipolar, the main processes driving turbulence are flow breaking/mixing, perhaps combined with turbulence ageing and non-cascade related multi-scale energy sources.